35.3 Celiac Disease & Malabsorption Syndromes

ABFM Family Medicine Certification Study Guide Exam

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1 Chapter 1: Exam Structure, Blueprint & Clinical Decision-Making

1.1 Exam Blueprint, FMCLA vs. One-Day Exam & Board Scoring 1.2 Clinical Reasoning, Test-Taking Strategy & Ambiguity Management 1.3 Evidence-Based Medicine & Clinical Practice Guidelines in Primary Care

2 Chapter 2: Healthcare Systems, Practice Management & Quality

2.1 Practice Management, Billing, Coding & Documentation 2.2 Quality Improvement, Patient Safety & Diagnostic Stewardship 2.3 Interprofessional Team-Based Care & Care Coordination

3 Chapter 3: Ethics, Law, Biostatistics & Health Equity

3.1 Medical Ethics, Informed Consent & Surrogate Decision-Making 3.2 Biostatistics, Clinical Epidemiology & Diagnostic Test Interpretation 3.3 Social Determinants of Health, Health Equity & Cultural Humility 3.4 Physician Wellness, Burnout Prevention & Professionalism

4 Chapter 4: Lifestyle Counseling & Behavior Change

4.1 Alcohol Use Screening & Brief Intervention 4.2 Illicit Drug & Cannabis Counseling 4.3 Tobacco & Vaping Cessation Counseling

5 Chapter 5: Nutrition, Physical Activity & Chronic Disease Prevention

5.1 Dietary Counseling for Obesity & Chronic Disease Prevention 5.2 Exercise Prescription & Physical Activity Counseling 5.3 Genetic Risk Assessment & Family History Counseling

6 Chapter 6: Routine Adult Immunizations

6.1 ACIP Adult Respiratory Vaccines: Influenza, COVID-19, RSV & Pneumococcal 6.2 ACIP Adult Non-Respiratory Vaccines: Tdap, Shingrix, HPV & Hep B 6.3 Immunizations in Special Populations: Pregnancy, Asplenia & Immunocompromise

7 Chapter 7: Pediatric Health Maintenance & Surveillance

7.1 Newborn Examination & Early Postnatal Care 7.2 Well-Child Care, Developmental Surveillance & Milestones 7.3 Pediatric & Adolescent Screening: Vision, Hearing, Anemia & Lead 7.4 Pediatric Oral Health, Dental Screening & Fluoride

8 Chapter 8: Behavioral Health & Safety Screening

8.1 Primary Care Depression, Anxiety & Behavioral Health Screening 8.2 Domestic Violence, Intimate Partner Violence & Firearm Safety 8.3 Occupational Health & Recreational Safety Counseling

9 Chapter 9: Adult Preventive Screening: Cardiovascular & Metabolic

9.1 Cardiovascular Disease & Hypertension Screening 9.2 Type 2 Diabetes Screening & Prediabetes Risk Stratification 9.3 Abdominal Aortic Aneurysm & Osteoporosis Screening

10 Chapter 10: Adult Cancer Screening: Breast & Gynecologic

10.1 Breast Cancer Screening & Risk-Assessment 10.2 Cervical Cancer Screening & ASCCP Algorithms 10.3 Skin Cancer Clinical Assessment & Counseling

11 Chapter 11: Adult Cancer Screening: Colorectal, Lung & Prostate

11.1 Colorectal Cancer Screening Modalities & Intervals 11.2 Lung Cancer Screening with Low-Dose CT 11.3 Prostate Cancer Screening & Shared Decision-Making

12 Chapter 12: Sexual Health, Infectious Disease Screening & Contraception

12.1 Sexual Health Counseling & Risk-Reduction Strategies 12.2 STI Screening: Chlamydia, Gonorrhea, Syphilis & Trichomoniasis 12.3 Bloodborne Infectious Disease Screening: HIV & Hepatitis C

13 Chapter 13: Reproductive Life Planning, Lactation & Preoperative Care

13.1 Preconception Planning & Comprehensive Contraception Management 13.2 Lactation Support & Breastfeeding Counseling 13.3 Preoperative Medical Evaluation & Pre-Participation Sports Exam

14 Chapter 14: Emergent Cardiovascular Conditions

14.1 Acute Coronary Syndromes & Myocardial Infarction 14.2 Acute Chest Pain Risk Stratification & Triage 14.3 Acute or Critical Valvular Heart Emergencies

15 Chapter 15: Cardiac Arrhythmias, Heart Failure & Hypertensive Crises

15.1 Acute Atrial & Ventricular Arrhythmias 15.2 Acute Decompensated Heart Failure & Cardiogenic Shock 15.3 Hypertensive Emergency & Urgency Management

16 Chapter 16: Vascular & Thromboembolic Emergencies

16.1 Pulmonary Embolism & Deep Vein Thrombosis 16.2 Acute Aortic Syndromes & Peripheral Vascular Emergencies 16.3 Critical Limb Ischemia & Acute Arterial Occlusion

17 Chapter 17: Neurologic Emergencies: Stroke & Altered Consciousness

17.1 Acute Ischemic Stroke & Intracranial Hemorrhage 17.2 Syncope Evaluation & Status Epilepticus 17.3 Acute Delirium, Encephalopathy & Severe Confusion

18 Chapter 18: Neurologic Trauma & Acute Cranial Emergencies

18.1 Concussion, Moderate-to-Severe TBI & Intracranial Injury 18.2 Thunderclap & Acute Severe Secondary Headaches 18.3 Acute Ophthalmologic Emergencies

19 Chapter 19: Acute Abdominal, Pelvic & Gastrointestinal Emergencies

19.1 Acute Abdominal & Pelvic Pain Triage 19.2 Upper & Lower Gastrointestinal Bleeding 19.3 Acute Hepatic Failure, Cholangitis & Severe Jaundice

20 Chapter 20: Acute Pulmonary & Airway Emergencies

20.1 Acute Hypoxic Respiratory Failure & ARDS 20.2 Severe Community-Acquired Pneumonia & Empyema 20.3 Acute Severe Epistaxis & Airway Obstruction

21 Chapter 21: Acute Traumatic Injuries & Wound Care

21.1 Major Trauma Resuscitation & Initial Assessment 21.2 Burn Assessment, Inhalation Injury & Resuscitation 21.3 Laceration Management, Complex Wounds & Animal Bites

22 Chapter 22: Acute Orthopedic & Musculoskeletal Emergencies

22.1 Acute Ambulatory Fractures & Initial Splinting 22.2 Compartment Syndrome & Major Orthopedic Trauma 22.3 Septic Arthritis & Acute Microcrystalline Crises

23 Chapter 23: Severe Infections, Sepsis & Systemic Emergencies

23.1 Sepsis, Septic Shock & Initial Fluid Resuscitation 23.2 Necrotizing Soft Tissue Infections & Severe CNS Infections 23.3 Anaphylaxis Diagnosis, Epinephrine Dosing & Airway Protection

24 Chapter 24: Metabolic, Endocrine & Electrolyte Emergencies

24.1 Diabetic Ketoacidosis & Hyperosmolar Hyperglycemic State 24.2 Critical Electrolyte Emergencies: Dyskalemias & Dysnatremias 24.3 Severe Calcium Abnormalities & Acute Adrenal Crisis

25 Chapter 25: Hematologic, Urologic & Dental Emergencies

25.1 Severe Symptomatic Anemias & Coagulopathic Emergencies 25.2 Testicular Torsion, Priapism & Acute Urinary Retention 25.3 Urgent Odontogenic Infections & Dental Trauma

26 Chapter 26: Psychiatric, Behavioral & Obstetric/Gynecologic Emergencies

26.1 Suicidal Ideation, Acute Agitation & Behavioral Emergencies 26.2 Acute Physical & Sexual Assault Care 26.3 Life-Threatening Vaginal Bleeding & Ectopic Pregnancy 26.4 Environmental Heat Stroke & Severe Hypothermia

27 Chapter 27: Acute Head, Neck & Neurologic Symptoms

27.1 Primary Acute Headaches: Migraine, Tension & Cluster 27.2 Concussion & Minor Closed Head Injury Evaluation 27.3 Transient Ischemic Attack Evaluation & ABCD2 Risk Scoring

28 Chapter 28: Acute Cranial Nerves, Hearing & Sensory Symptoms

28.1 Peripheral Neuropathies: Bell's Palsy, Carpal Tunnel & Radiculopathy 28.2 Acute Tinnitus, Sudden Sensorineural Hearing Loss & Cerumen Impaction 28.3 Acute Dizziness, Benign Paroxysmal Positional Vertigo & Vestibular Neuritis

29 Chapter 29: Acute Upper Respiratory Tract Infections

29.1 Acute Viral Rhinosinusitis vs. Bacterial Rhinosinusitis 29.2 Acute Pharyngitis: Group A Streptococcus & Centor Criteria 29.3 Acute Otitis Media, Otitis Externa & Serous Effusion

30 Chapter 30: Acute Lower Respiratory Infections & Cough

30.1 Influenza, COVID-19 & Viral Respiratory Syndromes 30.2 Acute Bronchitis & Lower Respiratory Tract Infections 30.3 Ambulatory Community-Acquired Pneumonia

31 Chapter 31: Allergic, Nasal & Non-Infectious Pulmonary Conditions

31.1 Allergic Rhinitis & Acute Non-Anaphylactic Allergic Reactions 31.2 Acute Dyspnea in Ambulatory Care 31.3 Interstitial Lung Diseases & Sarcoidosis Presentation

32 Chapter 32: Acute Chest, Cardiac & Vascular Symptoms

32.1 Palpitations Evaluation & Arrhythmia Triage in Primary Care 32.2 Deep Vein Thrombosis & Superficial Thrombophlebitis 32.3 Ambulatory Hypotension & Orthostasis Evaluation

33 Chapter 33: Acute Upper Gastrointestinal Conditions

33.1 Peptic Ulcer Disease & Gastritis 33.2 Dysphagia, Esophagitis & Acute Esophageal Disorders 33.3 Acute Nausea, Vomiting & Foodborne Illness

34 Chapter 34: Acute Lower Gastrointestinal Conditions

34.1 Acute Infectious Diarrhea & Gastroenteritis 34.2 Acute Constipation & Functional Bowel Changes 34.3 Ano-Rectal Disorders: Hemorrhoids, Fissures, Abscesses & Pruritus Ani

35 Chapter 35: Inflammatory, Functional & Malabsorptive GI Disorders

35.1 Acute Flares of Inflammatory Bowel Disease 35.2 Irritable Bowel Syndrome: Diagnosis, Subtyping & Management 35.3 Celiac Disease & Malabsorption Syndromes

36 Chapter 36: Acute Abdominal, Hepatic & Biliary Disorders

36.1 Ambulatory Abdominal & Pelvic Pain Triage 36.2 Acute Cholecystitis, Biliary Colic & Pancreatitis 36.3 Acute Liver Injury & Viral Hepatitis

37 Chapter 37: Acute Abdominal Wall, Hernias & Dental Conditions

37.1 Abdominal Wall, Inguinal & Ventral Hernias 37.2 Acute Dental Pain, Odontogenic Abscess & Aphthous Ulcers 37.3 Acute Edema: Unilateral vs. Bilateral Diagnostic Evaluation

38 Chapter 38: Acute Infectious Dermatoses

38.1 Bacterial Skin Infections: Impetigo, Cellulitis & Cutaneous Abscesses 38.2 Fungal Skin Infections: Tinea Corporis, Cruris, Pedis & Onychomycosis 38.3 Viral Cutaneous Infections: Herpes Simplex, Zoster & Molluscum Contagiosum

39 Chapter 39: Inflammatory, Allergic & Autoimmune Dermatoses

39.1 Atopic Dermatitis, Contact Dermatitis & Eczematous Flares 39.2 Non-Infectious Rashes: Urticaria, Drug Eruptions & Erythema Multiforme 39.3 Cutaneous Malignancies & Premalignant Lesions: AK, BCC, SCC & Melanoma

40 Chapter 40: Acute Shoulder, Elbow & Upper Extremity Injuries

40.1 Rotator Cuff Pathology, Tendinopathy & Shoulder Impingement 40.2 Lateral & Medial Epicondylitis, Olecranon Bursitis & Elbow Sprains 40.3 Wrist & Hand Soft-Tissue Injuries: De Quervain, TFCC & Finger Sprains

41 Chapter 41: Acute Knee, Ankle & Lower Extremity Injuries

41.1 Meniscal Tears, Ligamentous Knee Injuries & Patellofemoral Pain 41.2 Ankle Sprains, Ottawa Ankle Rules & Achilles Tendinopathy 41.3 Plantar Fasciitis, Shin Splints & Overuse Syndromes

42 Chapter 42: Acute Ambulatory Fractures & Dislocations

42.1 Distal Radius, Scaphoid & Common Upper Extremity Fractures 42.2 Metatarsal, Clavicle & Common Lower Extremity Fractures 42.3 Joint Dislocation Management: Nursemaid's Elbow & Shoulder Subluxation

43 Chapter 43: Acute Axial Musculoskeletal Pain & Falls

43.1 Acute Low Back Pain: Red Flags, Strain & Disc Herniation 43.2 Acute Cervical Strain, Whiplash & Axial Neck Pain 43.3 Evaluation of Falls in Ambulatory & Older Patients

44 Chapter 44: Acute Inflammatory Arthropathies & Generalized Pain

44.1 Acute Inflammatory Arthritis & Spondyloarthropathies 44.2 Myalgias, Rhabdomyolysis & Post-Viral Pain Syndromes 44.3 Acute Non-Headache Pain Management Strategies

45 Chapter 45: Acute Renal, Urinary & Genitourinary Conditions

45.1 Uncomplicated UTI, Pyelonephritis & Acute Urethritis 45.2 Hematuria Workup & Glomerulonephritis 45.3 Nephrolithiasis & Acute Urinary Tract Obstruction

46 Chapter 46: Acute Male Genitourinary & Prostatic Conditions

46.1 Acute Prostatitis, Epididymitis & Orchitis 46.2 Acute Scrotal Pain: Torsion vs Appendage, BPH & Male Genital Emergencies 46.3 Acute Urinary Retention & Incontinence Evaluation

47 Chapter 47: Acute Women's Health & Early Pregnancy Care

47.1 Early Pregnancy Diagnosis, Dating & Initial Complications 47.2 Abnormal Uterine Bleeding & Acute Menstrual Disorders 47.3 Premenstrual Syndrome & Premenstrual Dysphoric Disorder

48 Chapter 48: Breast Disorders, STIs & Pediatric Elimination

48.1 Palpable Breast Mass, Mastitis & Nipple Discharge 48.2 Sexually Transmitted Infections: Diagnosis, Staging & CDC Guidelines 48.3 Pediatric Enuresis & Encopresis

49 Chapter 49: Systemic Signs, Metabolic Dysregulation & Miscellaneous Infections

49.1 Acute Fever, Sepsis Screening & FUO in Primary Care 49.2 Acute Hyperglycemia & Symptomatic Hypoglycemia 49.3 Electrolyte Abnormalities: Mild-to-Moderate Disturbances 49.4 Vector-Borne, Tick-Borne & Rickettsial Illnesses

50 Chapter 50: Chronic Cardiovascular Diseases: Hypertension & Ischemia

50.1 Essential Hypertension Management: 2025 AHA/ACC Guideline & JNC Strategies 50.2 Chronic Coronary Artery Disease & Post-MI Secondary Prevention 50.3 Chronic Heart Failure: HFrEF, HFpEF & Quadruple GDMT

51 Chapter 51: Chronic Vascular, Valvular & Dyslipidemic Diseases

51.1 Peripheral Arterial Disease & Claudication 51.2 Chronic Valvular Heart Disease & Murmur Evaluation 51.3 Lipid Disorders & ASCVD Risk-Based Statin Therapy

52 Chapter 52: Chronic Respiratory Diseases: Asthma & COPD

52.1 Chronic Asthma Management: GINA Stepwise SMART Therapy 52.2 Chronic Obstructive Pulmonary Disease: GOLD Recommendations 52.3 Solitary Pulmonary Nodule Evaluation & Fleischner Society Criteria

53 Chapter 53: Chronic Metabolic Diseases: Diabetes Mellitus

53.1 Type 2 Diabetes Management: ADA Pharmacotherapy Algorithms 53.2 Type 1 Diabetes: Basal-Bolus Insulin, CGMs & Diabetic Complications 53.3 Diabetic Microvascular & Macrovascular Disease Surveillance

54 Chapter 54: Obesity, Nutrition & Metabolic Bone Diseases

54.1 Medical & Behavioral Management of Obesity & Incretin Mimetics 54.2 Osteoporosis & Metabolic Bone Disease: DEXA, FRAX & Antiresorptives 54.3 Nutritional Deficiencies: Vitamin D, B12, Iron & Malnutrition

55 Chapter 55: Chronic Endocrine Disorders

55.1 Primary & Subclinical Hypothyroidism, Hyperthyroidism & Nodules 55.2 Adrenal Disorders: Addison's Disease & Cushing's Syndrome 55.3 Hypercalcemia, Hyperparathyroidism & Pituitary Disorders

56 Chapter 56: Chronic Kidney Disease & Venous Disorders

56.1 Chronic Kidney Disease: KDIGO Staging & Renoprotective Therapy 56.2 Chronic Venous Insufficiency, Stasis Dermatitis & Lymphedema 56.3 Chronic Electrolyte & Acid-Base Management in CKD

57 Chapter 57: Chronic Gastrointestinal & Hepatic Diseases

57.1 Gastroesophageal Reflux Disease, Barrett's Esophagus & Dyspepsia 57.2 Chronic Liver Disease: MASLD/NAFLD, Cirrhosis & Portal Hypertension 57.3 Viral Hepatitis B & C: Long-Term Monitoring & DAA Therapy

58 Chapter 58: Colorectal Surveillance & Chronic Pancreaticobiliary Care

58.1 Post-Polypectomy Colorectal Polyp Surveillance Guidelines 58.2 Chronic Pancreatitis & Exocrine Pancreatic Insufficiency 58.3 Chronic Nausea, Gastroparesis & Functional GI Disorders

59 Chapter 59: Chronic Musculoskeletal & Rheumatologic Disorders

59.1 Osteoarthritis: Hip, Knee & Hand Management 59.2 Spinal Conditions: Spinal Stenosis, Spondylolisthesis & Compression Fractures 59.3 Chronic Myopathies & Fibromyalgia Syndrome

60 Chapter 60: Chronic Neurologic & Neurodegenerative Disorders

60.1 Dementia: Alzheimer's, Vascular & Lewy Body Disease 60.2 Parkinson's Disease & Essential Tremor 60.3 Epilepsy: Chronic Antiseizure Medications & Post-Stroke Care

61 Chapter 61: Chronic Peripheral Nerves, Pain & Sensory Disorders

61.1 Diabetic & Chronic Peripheral Neuropathies 61.2 Chronic Pain Syndromes & Chronic Daily Headaches 61.3 Chronic Tinnitus, Presbycusis & Persistent Dizziness

62 Chapter 62: Chronic Psychiatric Disorders

62.1 Major Depressive Disorder & Generalized Anxiety Disorder 62.2 Bipolar Disorder: Maintenance Pharmacotherapy & Lithium Monitoring 62.3 Adult & Pediatric Attention-Deficit/Hyperactivity Disorder

63 Chapter 63: Chronic Behavioral Health & Neurodevelopmental Conditions

63.1 Chronic Behavioral Conditions: PTSD, OCD & Somatization 63.2 Autism Spectrum Disorder & Intellectual Disabilities 63.3 Eating Disorders: Anorexia Nervosa, Bulimia & Binge Eating

64 Chapter 64: Chronic Substance Use Disorders & Tobacco Cessation

64.1 Alcohol Use Disorder: Pharmacotherapy & Relapse Prevention 64.2 Opioid & Stimulant Use Disorders: MOUD & Harm Reduction 64.3 Longitudinal Tobacco Cessation Pharmacotherapy

65 Chapter 65: Chronic Dermatologic Conditions

65.1 Acne Vulgaris, Rosacea & Seborrheic Dermatitis 65.2 Chronic Plaque Psoriasis & Biologic Therapies 65.3 Chronic Eczema, Hidradenitis Suppurativa & Cutaneous Lupus

66 Chapter 66: Chronic Reproductive, Infectious & Geriatric Special Care

66.1 Chronic Menstrual Disorders, Infertility & Sexual Dysfunction 66.2 Menopause Management & Hormone Replacement Therapy 66.3 Chronic HIV Infection Management & Primary Care Integration 66.4 Gender-Affirming Primary Care & Hormone Therapy 66.5 Advance Care Planning, Palliative Care & End-of-Life Symptom Control

67 Chapter 67: Continuity Care: Sleep, Fatigue, Cancer, Pregnancy & the Adult Preventive Visit

67.1 Chronic Insomnia & Obstructive Sleep Apnea 67.2 Chronic Malaise, Fatigue & ME/CFS 67.3 Primary Care During Cancer Treatment & Survivorship 67.4 Routine Prenatal Care & Longitudinal Pregnancy Management 67.5 The Periodic Adult Health Examination & Medicare Annual Wellness Visit

35.3 Celiac Disease & Malabsorption Syndromes

Key Takeaways Explain This Topic AI

Celiac disease (gluten-sensitive enteropathy) is an immune-mediated enteropathy triggered by ingestion of dietary gluten (gliadin fraction) in genetically susceptible individuals expressing HLA-DQ2 (>90%) or HLA-DQ8 (5-10%); tissue transglutaminase-2 (tTG) deamidates gliadin peptides, driving CD4+ T-cell activation, intraepithelial lymphocytosis, crypt hyperplasia, and progressive duodenal villous atrophy.

First-line serologic screening requires testing serum tissue Transglutaminase IgA (anti-tTG IgA) AND Total Serum IgA simultaneously; selective IgA deficiency occurs in 2% to 3% of celiac patients (10- to 15-fold higher than the general population), causing false-negative IgA serology that mandates reflex testing with IgG-based assays (deamidated gliadin peptide [DGP] IgG or anti-tTG IgG).

CRITICAL TESTING MANDATE: All serologic antibody tests and confirmatory duodenal mucosal biopsies must be performed while the patient is actively consuming a gluten-containing diet (minimum of 1 to 2 slices of wheat bread daily for 6 to 12 weeks); premature gluten withdrawal results in false-negative serology and histological healing.

Dermatitis herpetiformis is the pathognomonic cutaneous manifestation of celiac disease, presenting with intensely pruritic, grouped papulovesicles on extensor surfaces (elbows, knees, buttocks); direct immunofluorescence of perilesional normal skin demonstrates granular IgA deposition in dermal papillae, responding to oral dapsone and a strict lifelong gluten-free diet.

Malabsorption syndromes must be systematically differentiated: Exocrine Pancreatic Insufficiency (EPI: chronic pancreatitis, cystic fibrosis; diagnosed by fecal elastase-1 <200 mcg/g; treated with pancreatic enzyme replacement therapy [PERT]), Small Intestinal Bacterial Overgrowth (SIBO: diagnosed by hydrogen/methane breath test; treated with rifaximin 550 mg TID x 14 days), and Lactose Intolerance (brush-border lactase deficiency; managed with dietary restriction or lactase enzymes).

Last updated: September 2026

Pathophysiology & Genetic Architecture of Celiac Disease

Celiac disease (gluten-sensitive enteropathy) is an immune-mediated systemic inflammatory disorder triggered by the dietary ingestion of gluten proteins in genetically susceptible individuals. It affects approximately 1% of the global population, with an estimated 60% to 70% of affected individuals in the United States remaining undiagnosed due to atypical, non-classical, or subclinical presentations.

Molecular Immunopathogenesis

The Antigenic Culprit (Gluten) :

Gluten is the major storage protein found in wheat (gliadins and glutenins), barley (hordeins), and rye (secalins). (Oats contain avenins, which are non-toxic in >95% of patients unless contaminated during agricultural milling).

The gliadin fraction is exceptionally rich in proline and glutamine residues. Because human gastric pepsins, pancreatic endopeptidases, and brush-border carboxypeptidases lack the enzymatic capacity to cleave post-proline peptide bonds, an intact 33-mer gliadin peptide survives luminal enzymatic digestion.

Deamidation by Tissue Transglutaminase-2 (tTG-2) :

Surviving gliadin fragments breach the intestinal epithelial barrier via paracellular transudation or transcellular endocytosis into the lamina propria.

In the lamina propria, the endogenous calcium-dependent enzyme tissue Transglutaminase-2 (tTG-2) post-translationally deamidates neutral glutamine residues into negatively charged glutamic acid .

MHC Class II Recognition & T-Cell Activation :

Negatively charged deamidated gliadin peptides fit with high stereochemical affinity into the positively charged peptide-binding grooves of Human Leukocyte Antigen (HLA) class II heterodimers : HLA-DQ2 (encoded by DQA1*05:01 and DQB1*02:01 , present in 90-95% of celiac patients) or HLA-DQ8 (encoded by DQA1*03:01 and DQB1*02:02 , present in 5-10%).

Antigen-presenting cells (dendritic cells and macrophages) present these peptides to CD4+ T-helper cells, which trigger a vigorous Th1/Th17 immune response characterized by the secretion of interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), and interleukin-21.

Enterocyte Destruction & Humoral Response :

Concurrently, enterocytes stressed by gliadin upregulate Interleukin-15 (IL-15) and surface non-classical MHC molecules (MICA/MICB). IL-15 reprograms CD8+ cytotoxic intraepithelial lymphocytes (IELs) into natural killer-like killer cells expressing NKG2D receptors, which directly lyse enterocytes, leading to progressive mucosal architectural destruction.

Activated B cells differentiate into plasma cells that synthesize antibodies directed against deamidated gliadin peptides (DGP) and the autoantigen tissue transglutaminase (anti-tTG) , as well as anti-endomysial antibodies (EMA) .

Histopathologic Marsh Staging

Confirmatory duodenal histology is staged using the validated Marsh-Oberhuber criteria:

Marsh 0 (Pre-infiltrative) : Normal mucosal architecture.

Marsh 1 (Infiltrative) : Normal villous architecture, but intraepithelial lymphocytosis (>25 IELs per 100 enterocytes).

Marsh 2 (Hyperplastic) : Intraepithelial lymphocytosis accompanied by crypt hyperplasia (elongated crypts with increased mitotic figures).

Marsh 3 (Destructive - Diagnostic Hallmark) : Intraepithelial lymphocytosis, crypt hyperplasia, and progressive villous atrophy :

• Marsh 3a : Partial villous blunting;
• Marsh 3b : Subtotal villous atrophy (stunted, thin villi);

Marsh 3c : Total villous atrophy (completely flat mucosa with total loss of villous projections, resembling colonic architecture).

Clinical Spectrum: Classic, Non-Classic & Dermatitis Herpetiformis

The clinical presentation of celiac disease has shifted dramatically over recent decades. The historic paradigm of a severely wasted infant with protuberant abdomen and foul steatorrhea now represents the minority of adult cases.

1. Classic (Malabsorptive) Celiac Disease

Presents with overt symptoms of intestinal malabsorption: chronic watery or greasy diarrhea, steatorrhea (pale, voluminous, malodorous floating stools), significant unintentional weight loss, abdominal distension, muscle wasting, and severe nutritional deficiencies.

Fat-soluble vitamin malabsorption:

• Vitamin A deficiency : Night blindness (nyctalopia), xerophthalmia, follicular hyperkeratosis;
• Vitamin D & Calcium deficiency : Hypocalcemia, secondary hyperparathyroidism, osteomalacia, tetany;
• Vitamin E deficiency : Peripheral neuropathy, spinocerebellar ataxia, hemolytic anemia;

Vitamin K deficiency : Hypoprothrombinemia, elevated INR, easy bruising, ecchymoses, hematuria.

2. Non-Classic (Extraintestinal) Celiac Disease

Now accounting for >60% of newly diagnosed adult cases in primary care. Patients have minimal or no overt gastrointestinal symptoms, presenting instead with subtle extraintestinal signs:

Refractory Iron Deficiency Anemia : The most common extraintestinal manifestation. Because dietary iron is absorbed almost exclusively in the duodenum and proximal jejunum (the anatomical epicenter of celiac villous destruction), impaired enterocyte iron transport leads to microcytic anemia that fails to respond to oral iron supplementation.

Metabolic Bone Disease : Early-onset osteopenia, osteoporosis, or low-trauma fragility fractures in young adults or premenopausal women, driven by chronic calcium malabsorption and vitamin D deficiency.

Unexplained Transaminitis ("Celiac Hepatitis") : Asymptomatic, mild-to-moderate elevations in serum AST and ALT (typically 1.5 to 3 times upper limit of normal) found in up to 10% to 15% of patients. In >80% of cases, liver enzymes normalize completely within 6 to 12 months on a strict gluten-free diet.

Neurologic & Psychiatric Manifestations : Symmetric distal sensory peripheral neuropathy, gluten ataxia (cerebellar ataxia with Purkinje cell loss and anti-gliadin antibodies), intractable migraine headaches, anxiety, and depression.

Oral & Cutaneous Signs : Recurrent, painful aphthous stomatitis (oral ulcers) and permanent dental enamel hypoplasia (pitting or yellow/brown horizontal grooves affecting secondary teeth).

Reproductive Dysfunction : Unexplained primary or secondary infertility, recurrent spontaneous miscarriages, intrauterine growth restriction (IUGR), and delayed menarche.

3. Dermatitis Herpetiformis: The Pathognomonic Cutaneous Manifestation

Clinical Presentation : Intensely pruritic, burning, stinging erythematous macules, urticarial papules, and grouped vesicles ("herpetiform" clusters) distributed symmetrically over the extensor surfaces:

• Elbows and forearms (90%)
• Knees and shins (30%)
• Buttocks and natal cleft (80%)

Posterior scalp and upper back.

Pathognomonic Diagnostic Test : Direct Immunofluorescence (DIF) performed on a punch biopsy of perilesional (normal-appearing) skin adjacent to an active lesion .

Microscopic Finding : Sinuous, granular IgA deposits localized to the dermal papillae along the dermal-epidermal junction.

Gastrointestinal Correlation : Over 90% of patients with dermatitis herpetiformis have biopsy-confirmed intestinal enteropathy (villous atrophy), although gastrointestinal symptoms are frequently subclinical or mild.

Clinical Mandate : A definitive diagnosis of dermatitis herpetiformis via skin biopsy is diagnostic of celiac disease ; confirmatory duodenal biopsy is not strictly required.

Therapeutic Strategy :

Oral Dapsone (50 to 100 mg daily) : Provides dramatic symptomatic relief, arresting pruritus and resolving skin lesions within 24 to 72 hours by inhibiting neutrophil chemotaxis and myeloperoxidase release. Check G6PD enzyme level prior to initiation to prevent severe drug-induced hemolytic anemia.

Strict Lifelong Gluten-Free Diet : Dapsone treats only the cutaneous symptoms and has zero effect on intestinal mucosal damage or lymphoma risk . A strict gluten-free diet heals the intestinal mucosa and, over 6 to 24 months, eliminates cutaneous IgA clearance, allowing dapsone to be successfully tapered and discontinued.

Diagnostic Testing Protocol & The Selective IgA Deficiency Pitfall

Establishing an accurate diagnosis requires a structured serologic and endoscopic algorithm while adhering to critical pre-test dietary rules: CELIAC DISEASE DIAGNOSTIC PROTOCOL

• Patient Suspected of Celiac Disease (Must be ON Gluten Diet!)
• │
• ▼

Order FIRST-LINE Serologic Screening:

• Serum Tissue Transglutaminase IgA (anti-tTG IgA)
• PLUS Total Serum IgA Level
• │
• ┌──────────────────────┴──────────────────────┐
• ▼ ▼
• Total Serum IgA NORMAL Total Serum IgA DEFICIENT
• (IgA Sufficient) (IgA <20 mg/dL)
• │ │
• ┌──────┴──────┐ ┌──────┴──────┐
• ▼ ▼ ▼ ▼
• anti-tTG IgA anti-tTG IgA DGP IgG or DGP IgG or
• POSITIVE NEGATIVE anti-tTG IgG anti-tTG IgG
• │ │ POSITIVE NEGATIVE
• │ Celiac Unlikely │ │
• │ (Look for SIBO/EPI) │ Celiac Unlikely
• │ │
• └──────────────────────┬──────────────────────┘
• │
• ▼
• Confirmatory Upper Endoscopy (EGD)

• Multiple Duodenal Biopsies:

• 1 to 2 biopsies from Duodenal Bulb
• At least 4 biopsies from Distal Duodenum (D2/D3)
• Histology: Marsh 1-3 (Villous atrophy, crypt hyperplasia)
• │
• ▼
• Initiate Lifelong Strict GFD
• 1. First-Line Serology & Total IgA Requirement

Tissue Transglutaminase IgA (anti-tTG IgA) :

Sensitivity: 95% to 98%; Specificity: 95% to 98%.

The single preferred first-line serologic test for patients aged >2 years.

Total Serum IgA Measurement :

Important

THE SELECTIVE IgA DEFICIENCY PITFALL : Selective IgA deficiency occurs in 2% to 3% of patients with celiac disease , representing a 10- to 15-fold higher prevalence than in the general population (where it occurs in ~1:600).

In an IgA-deficient patient, the immune system cannot produce IgA antibodies; consequently, anti-tTG IgA and anti-endomysial IgA will be FALSELY NEGATIVE , leading to missed diagnoses and progressive untreated disease.

Mandatory Clinical Protocol : Every celiac serologic screening panel must include Total Serum IgA .

If Total Serum IgA is below the lower limit of normal (<20 mg/dL), reflex testing must immediately evaluate IgG-based serology : Deamidated Gliadin Peptide IgG (DGP IgG) OR anti-tTG IgG .

Anti-Endomysial IgA Antibodies (EMA-IgA) :

Binds to tTG in the perimysium of smooth muscle. Highest specificity (near 100%), but lower sensitivity in early disease and requires indirect immunofluorescence (operator-dependent). Used primarily as a confirmatory secondary test.

2. THE CRITICAL GLUTEN CHALLENGE RULE

Caution

NEVER INITIATE A GLUTEN-FREE DIET PRIOR TO DIAGNOSTIC TESTING! All serologic antibody titers (anti-tTG, anti-DGP) and endoscopic intestinal mucosal lesions depend strictly on ongoing dietary gluten exposure. When gluten is eliminated, antibody titers decline exponentially (half-life of anti-tTG is ~30 to 60 days) and duodenal villous architecture completely normalizes, producing falsely negative serology and histologically normal biopsies .

The Standard Gluten Challenge Protocol :

If a symptomatic patient has already placed themselves on a gluten-free diet before testing, they must undergo a formal gluten challenge:

Consume at least 3 to 10 grams of dietary gluten daily (equivalent to 1 to 2 slices of standard wheat bread or one bowl of wheat pasta daily);

Continue this active consumption for a minimum of 6 to 12 weeks ;

Serologic testing and duodenal biopsies are then performed while actively on this diet.

3. Confirmatory Esophagogastroduodenoscopy (EGD) & Duodenal Biopsy Protocol

In adult clinical practice, definitive confirmation of celiac disease requires an upper endoscopy with mucosal biopsy:

Biopsy Sampling Requirements :

Because celiac villous atrophy can be focal or patchy, inadequate sampling leads to false-negative pathology.

At least 1 to 2 biopsies must be taken from the duodenal bulb (often the only site of involvement, classically at the 9- or 12-o'clock position);

PLUS at least 4 biopsies from the second and third portions of the distal duodenum (D2/D3) .

A minimum total of 5 to 6 biopsies is required.

Endoscopic Visual Clues :

• Scalloping of duodenal mucosal folds;
• Mosaic or cracked-clay mucosal pattern;
• Flattened, reduced, or absent duodenal circular folds (valvulae conniventes);

Mucosal nodularity.

4. Utility & Interpretation of HLA-DQ2 / HLA-DQ8 Genetic Testing

Human leukocyte antigen (HLA) genotyping detects the alleles encoding HLA-DQ2 ( DQA1*05:01, DQB1*02:01 ) and HLA-DQ8 ( DQA1*03:01, DQB1*03:02 ).

High Sensitivity & Negative Predictive Value (>99%) :

Over 99% of celiac patients carry HLA-DQ2 or HLA-DQ8. If a patient tests negative for both HLA-DQ2 and HLA-DQ8, celiac disease is virtually 100% ruled out .

Low Specificity & Positive Predictive Value (~12-15%) :

Approximately 30% to 40% of the healthy, asymptomatic general population carries HLA-DQ2 or DQ8 without ever developing celiac disease. Therefore, a positive HLA test is NOT diagnostic and only indicates genetic susceptibility.

Appropriate Clinical Indications for HLA Testing :

Resolving diagnostic ambiguity when serology and duodenal histology are discordant (e.g., positive serology with Marsh 0-1 histology);

Evaluating a patient already established on a strict gluten-free diet who is unwilling or unable to undergo a formal 6-to-12-week gluten challenge (a negative result conclusively rules out celiac disease, avoiding the need for a challenge);

Screening asymptomatic individuals in high-risk populations (first-degree relatives of celiac patients, Type 1 diabetics, Down syndrome, Turner syndrome, autoimmune thyroiditis) to rule out future susceptibility.

Long-Term Management, Surveillance & Health Maintenance

Celiac disease is a chronic systemic condition requiring lifelong vigilance to prevent malignant transformation (enteropathy-associated T-cell lymphoma [EATL] and small bowel adenocarcinoma) and nutritional failure.

1. The Lifelong Strict Gluten-Free Diet (GFD)

Complete, permanent avoidance of all dietary products containing wheat, rye, and barley (including hidden additives: malt, malt extract, hydrolyzed wheat protein, soy sauces brewed with wheat, beer, ale, and food thickeners).

Pure, uncontaminated oats (certified gluten-free) are safe and well-tolerated by >95% of patients and improve diet quality and dietary fiber intake.

Consultation with a specialized gastrointestinal registered dietitian experienced in celiac disease is mandatory upon diagnosis.

2. Baseline Nutritional Screening & Bone Mineral Density Evaluation

At the time of diagnosis, all adult patients must undergo baseline screening for malabsorptive micronutrient deficiencies:

• Complete blood count, serum ferritin, total iron-binding capacity (TIBC);
• Serum folate and Vitamin B12;
• 25-hydroxyvitamin D, serum calcium, phosphorus, alkaline phosphatase;
• Serum zinc and copper levels;
• Hepatic panel (AST, ALT) and TSH;

Dual-Energy X-ray Absorptiometry (DEXA) Scan : Recommended at baseline in all adult celiac patients to screen for osteopenia and osteoporosis; repeat at 2 to 3 years if initial scan is abnormal.

3. Serologic Surveillance & Monitoring Healing

Measure serum anti-tTG IgA titers at 6 months and 12 months following GFD initiation, and annually thereafter once normalized.

Antibody titers decline gradually as dietary antigen is eliminated; failure of titers to drop significantly by 6 to 12 months strongly indicates inadvertent or occult gluten exposure (which accounts for >90% of non-responsive celiac disease).

Repeat upper endoscopy with biopsy is recommended at 2 years for patients with severe initial presentation, persistent symptoms, or persistent seropositivity to document mucosal healing.

4. Pneumococcal Immunization & Functional Hyposplenism

Functional Hyposplenism : Occurs in up to one-third of adult celiac patients due to splenic reticuloendothelial atrophy, predisposing to catastrophic bacteremia caused by encapsulated organisms, predominantly Streptococcus pneumoniae .

Immunization Guideline : All adults with celiac disease should receive pneumococcal vaccination (a single dose of PCV20, or PCV15 followed by PPSV23 ≥1 year later).

Malabsorption Differential Diagnosis: EPI, SIBO & Lactase Deficiency

When a patient presents with chronic diarrhea, weight loss, bloating, and nutritional failure, celiac disease must be systematically differentiated from other classic malabsorptive entities:

Differential Diagnostic Comparison Table

Feature / Parameter Celiac Disease Exocrine Pancreatic Insufficiency (EPI) Small Intestinal Bacterial Overgrowth (SIBO) Primary Lactose Intolerance

Underlying Pathophysiology Autoimmune enteropathy; duodenal villous atrophy and brush-border enzyme loss Inadequate intraluminal secretion of pancreatic lipase, protease, and amylase Excessive colonic-type bacterial proliferation (>10³ CFU/mL) in small intestine Genetically programmed reduction in brush-border lactase-phlorizin hydrolase activity

Classic Etiologies Gluten exposure in HLA-DQ2/DQ8 hosts Chronic pancreatitis (alcohol, idiopathic), cystic fibrosis, pancreatectomy Motility disorders (scleroderma, diabetes), strictures, bypass surgery, chronic PPI use Adult-type hypolactasia (common in Asian, African, and Native American ancestry)

Stool Characteristics Watery to greasy, pale, bulky, foul-smelling Severe steatorrhea : oily, floating, glistening stools; orange oil droplets in toilet bowl Watery diarrhea, prominent bloating, flatulence, floating foul stools Explosive, watery, frothy stools; acidic pH (<5.5); prominent perianal excoriation

Specific Nutritional Deficiencies Iron , Calcium, Vitamin D, Folate, Fat-soluble vitamins (A, D, E, K) Severe fat-soluble vitamin deficiencies (A, D, E, K); normal iron and folate absorption Vitamin B12 deficiency (bacterial consumption); Elevated serum folate (bacterial synthesis) None (isolated carbohydrate malabsorption; normal fat, protein, and micronutrient absorption)

Diagnostic Gold Standard Anti-tTG IgA + Total IgA , confirmed by duodenal mucosal biopsy Fecal Elastase-1 (FE-1) : Level <200 mcg/g (<100 mcg/g = severe EPI) Glucose or Lactulose Hydrogen/Methane Breath Test (H2 rise ≥20 ppm; CH4 ≥10 ppm) 2-week empiric lactose-free dietary trial; Hydrogen breath test (H2 rise >20 ppm)

First-Line Pharmacotherapy Lifelong strict Gluten-Free Diet ; nutritional repletion Pancreatic Enzyme Replacement Therapy (PERT) : Enteric-coated pancrelipase with meals Oral Rifaximin 550 mg TID for 14 days ; treat underlying motility disorder Dietary lactose restriction; over-the-counter lactase enzyme replacement prior to dairy meals

Clinical Details on Non-Celiac Malabsorption Syndromes

Exocrine Pancreatic Insufficiency (EPI) :

Lipase output must decline by >90% before overt fat malabsorption and steatorrhea occur, because the pancreas has enormous functional reserve.

Fecal Elastase-1 (FE-1) is the diagnostic test of choice. Human pancreatic elastase-1 is entirely resistant to degradation during intestinal transit. Unlike 72-hour fecal fat quantification, the FE-1 test requires only a single solid or semi-formed stool sample. Crucially, exogenous pancreatic enzyme replacement therapy does NOT cross-react with the human elastase-1 ELISA assay , meaning the test remains completely accurate even if the patient is already taking PERT.

Management : Enteric-coated capsules containing lipase, amylase, and protease (e.g., Creon, Zenpep). Dosing begins at 40,000 to 50,000 USP units of lipase per major meal (and half dose with snacks), taken with the first bites of food. Concurrent proton pump inhibitor (PPI) therapy is often added to suppress gastric acid and prevent premature destruction of enzyme coatings in the duodenum.

Small Intestinal Bacterial Overgrowth (SIBO) :

Bacteria resident in the small bowel deconjugate bile salts, rendering them insoluble and preventing mixed micelle formation, resulting in fat malabsorption. Furthermore, bacteria avidly consume intraluminal Vitamin B12, causing macrocytic megaloblastic anemia. Paradoxically, bacteria synthesize folate and vitamin K, resulting in elevated serum folate levels in the setting of low Vitamin B12 (a classic board exam diagnostic clue!).

Diagnosis : Non-invasive carbohydrate breath testing . Ingestion of glucose or lactulose followed by serial end-expiratory breath measurements every 15 minutes for 2 hours. A rise in breath hydrogen of ≥20 parts per million (ppm) or breath methane ≥10 ppm within 90 minutes confirms the diagnosis.

Treatment : Oral Rifaximin 550 mg three times daily for 14 days . For methane-positive SIBO (associated with constipation and intestinal methanogen overgrowth [IMO] by Methanobrevibacter smithii ), combine rifaximin with oral neomycin (500 mg BID) or oral metronidazole (250 mg TID) for 14 days.

Primary Lactose Intolerance (Adult-Type Hypolactasia) :

Driven by genetically regulated downregulation of lactase gene ( LCT ) expression occurring after weaning in >70% of the world's population.

Undigested lactose disaccharides cannot be absorbed intact across enterocytes. In the small bowel lumen, lactose exerts an osmotic force, drawing fluid into the intestine. In the colon, bacterial fermentation converts lactose into short-chain fatty acids (SCFAs), carbon dioxide, and hydrogen gas.

Clinical Clue : Onset of loud borborygmi, crampy abdominal pain, flatulence, and explosive watery diarrhea within 30 minutes to 2 hours following dairy ingestion. Systemic nutrition, fat absorption, and serum laboratory studies are completely normal.

Loading diagram... Comprehensive Diagnostic Algorithm for Celiac Disease and Chronic Malabsorption