Study guide
2.3 Thyroid Function Testing & Hypothyroidism
ABIM Internal Medicine Exam
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1 Chapter 0: The ABIM Exam, Blueprint & Study Strategy
0.1 Exam Format, Question Types & the 2026 Blueprint 0.2 Eligibility, Registration, Fees & Exam-Day Logistics 0.3 Scoring, the Passing Standard & Score Reports 0.4 Building a Blueprint-Weighted Study Plan
2 Chapter 1: Cardiovascular Disease (14% of Exam)
1.1 Ischemic Heart Disease & Acute Coronary Syndromes 1.2 Antithrombotic Therapy, Secondary Prevention & Mechanical Complications of MI 1.3 Atrial Fibrillation, Atrial Flutter & Stroke Prevention 1.4 Supraventricular Tachycardias, Ventricular Arrhythmias & Bradycardias 1.5 Heart Failure: Classification, Staging & Guideline-Directed Medical Therapy 1.6 Device Therapy, HFpEF & the Cardiomyopathies 1.7 Valvular Heart Disease & Endocarditis Prophylaxis 1.8 Pericardial Disease & Acute Aortic Syndromes 1.9 Hypertension: Classification, Diagnosis & Secondary Causes 1.10 Hypertensive Crises & Dyslipidemia 1.11 Adult Congenital Heart Disease & Coarctation of the Aorta 1.12 Syncope: Reflex, Orthostatic & Cardiac Causes 1.13 Cardiac Physical Examination, Murmurs & Antithrombotic Selection
3 Chapter 2: Endocrinology, Diabetes & Metabolism (9% of Exam)
2.1 Diabetes Mellitus: Diagnosis, Glycemic Targets & Pharmacotherapy 2.2 Insulin Therapy, Hyperglycemic Emergencies & Chronic Complications 2.3 Thyroid Function Testing & Hypothyroidism 2.4 Thyrotoxicosis, Thyroid Storm & Thyroid Nodules 2.5 Adrenal & Pituitary Disorders 2.6 Hypercalcemia, Hypocalcemia & Disorders of Mineral Metabolism 2.7 Osteoporosis & Paget Disease of Bone 2.8 Ovarian, Testicular & Reproductive Endocrine Disorders 2.9 Hypoglycemia, Endocrine Tumors, Polyglandular Syndromes & Severe Hypertriglyceridemia
4 Chapter 3: Gastroenterology & Hepatology (9% of Exam)
3.1 Esophageal Disease 3.2 Stomach & Duodenal Disease and Gastrointestinal Hemorrhage 3.3 Inflammatory Bowel Disease 3.4 Celiac Disease & Irritable Bowel Syndrome 3.5 Diverticular Disease & Colorectal Cancer Screening 3.6 Viral Hepatitis, Steatotic & Alcohol-Associated Liver Disease 3.7 Cirrhosis & the Complications of Portal Hypertension 3.8 Acute Pancreatitis 3.9 Chronic Pancreatitis & Biliary Tract Disease 3.10 Inherited, Autoimmune & Drug-Induced Liver Disease 3.11 Small Intestinal Disease, Ischemia & Gastrointestinal Complications of HIV
5 Chapter 4: Infectious Disease (9% of Exam)
4.1 Lower Respiratory Tract Infections & Sepsis Syndromes 4.2 Viral Respiratory Pathogens & Tuberculosis 4.3 Central Nervous System Infections 4.4 Skin, Soft Tissue, Bone & Joint Infections 4.5 Infective Endocarditis & Cardiovascular Infection 4.6 Clostridioides difficile & Catheter-Related Bloodstream Infection 4.7 HIV Diagnosis, Antiretroviral Therapy & Prevention 4.8 Opportunistic Infections & Sexually Transmitted Infections 4.9 Fever of Unknown Origin, Neutropenic Fever & Toxic Shock 4.10 Travel-Related Illness, Vector-Borne Disease & Outbreaks 4.11 Infection Prevention, Nosocomial Infection & Postexposure Prophylaxis 4.12 Rheumatic Fever, Poststreptococcal Disease, Enteric & Hepatic Infections
6 Chapter 5: Pulmonary Disease (9% of Exam)
5.1 COPD: Diagnosis, GOLD Classification & Initial Pharmacotherapy 5.2 Interventions That Reduce COPD Mortality & Exacerbation Management 5.3 Asthma: Diagnosis, Stepwise Therapy & Status Asthmaticus 5.4 Interstitial Lung Disease & Idiopathic Pulmonary Fibrosis 5.5 Sarcoidosis, Hypersensitivity Pneumonitis & Occupational Lung Disease 5.6 Pulmonary Embolism: Diagnosis, Risk Stratification & Anticoagulation 5.7 Pulmonary Hypertension & Sleep-Disordered Breathing 5.8 Acute Respiratory Distress Syndrome & Mechanical Ventilation 5.9 Pleural Disease, Empyema & Pneumothorax 5.10 Bronchiectasis, Cystic Fibrosis & Restrictive Lung Disease 5.11 Evaluation of Cough, Dyspnea, Hemoptysis & the Solitary Pulmonary Nodule
7 Chapter 6: Rheumatology & Orthopedics (9% of Exam)
6.1 Rheumatoid Arthritis: Diagnosis & Systemic Manifestations 6.2 Antirheumatic Pharmacotherapy & the Spondyloarthropathies 6.3 Gout: Pathophysiology & Acute Management 6.4 Urate-Lowering Therapy & Calcium Pyrophosphate Deposition Disease 6.5 Osteoarthritis 6.6 Systemic Lupus Erythematosus 6.7 Systemic Sclerosis, Sjogren Syndrome & Inflammatory Myopathies 6.8 The Vasculitides 6.9 Regional Musculoskeletal Syndromes, Back Pain & Sports Injuries 6.10 Other Primary Rheumatic Disorders & Mixed Connective Tissue Disease 6.11 Osteonecrosis & Metabolic Bone Disease
8 Chapter 7: Hematology (6% of Exam)
7.1 Approach to Anemia & the Microcytic Anemias 7.2 Macrocytic, Normocytic & Hemolytic Anemias 7.3 Hemoglobinopathies, Thalassemias & Paroxysmal Nocturnal Hemoglobinuria 7.4 Platelet Disorders, Thrombocytopenia & the Bleeding Patient 7.5 Coagulation Factor Disorders, Thrombophilia & Anticoagulant Reversal 7.6 Acute Leukemias, Chronic Leukemias & Myeloproliferative Neoplasms 7.7 Lymphomas & Plasma Cell Disorders 7.8 Myelodysplastic Syndrome, Myeloproliferative Neoplasms & Porphyria 7.9 Transfusion Medicine & Late Complications of Transplantation
9 Chapter 8: Medical Oncology (6% of Exam)
8.1 Breast, Lung, Colorectal & Prostate Cancer 8.2 Oncologic Emergencies 8.3 Genitourinary & Gynecologic Malignancies 8.4 Head and Neck, Bone & Soft Tissue Cancer and Cancer of Unknown Primary 8.5 Complications of Cancer & Its Treatment 8.6 Cancer Prevention, Survivorship & Psychosocial Care
10 Chapter 9: Nephrology & Urology (6% of Exam)
9.1 Acute Kidney Injury: Staging, Etiology & Urine Microscopy 9.2 Glomerular Disorders & Nephrotic Syndrome 9.3 Nephritic Syndromes, RPGN & Indications for Renal Replacement Therapy 9.4 Chronic Kidney Disease: Staging & Progression Retardation 9.5 Complications of Chronic Kidney Disease: Anemia, CKD-MBD & Acidosis 9.6 Hyponatremia, Hypernatremia & Water Balance 9.7 Potassium Disorders & Systematic Acid-Base Analysis 9.8 Renal Tubular Acidosis & Nephrolithiasis 9.9 Prostate Disorders, Urinary Incontinence & Other Urologic Conditions 9.10 Cystic Kidney Disease, Obstructive Uropathy, Tubulointerstitial Disease & Hematuria
11 Chapter 10: Neurology (4% of Exam)
10.1 Acute Ischemic Stroke: Syndromes & Reperfusion 10.2 Transient Ischemic Attack, Secondary Prevention & Hemorrhagic Stroke 10.3 Headache & Facial Pain 10.4 Seizures, Epilepsy & Movement Disorders 10.5 Multiple Sclerosis & Neuromuscular Junction Disorders 10.6 Motor Neuron Disease & Acute Peripheral Neuropathy 10.7 Cranial Neuropathies & Neuro-Ophthalmology 10.8 Peripheral Neuropathies, CNS Tumors & Other Neurologic Disorders
12 Chapter 11: Psychiatry & Behavioral Health (4% of Exam)
11.1 Major Depressive Disorder & Medical Mimics 11.2 Antidepressant Pharmacotherapy & Treatment-Resistant Depression 11.3 Bipolar Disorder, Mood Stabilizers & Lithium Toxicity 11.4 Anxiety, Stress-Related & Obsessive-Compulsive Disorders 11.5 Alcohol Use Disorder & Withdrawal 11.6 Pharmacotherapy for Alcohol & Opioid Use Disorder 11.7 Toxidromes, Psychiatric Emergencies & Suicide Risk Assessment 11.8 Psychotic, Somatic Symptom, Factitious & Personality Disorders 11.9 Eating Disorders, Sleep Disorders & Sexual Health
13 Chapter 12: Dermatology (3% of Exam)
12.1 Dermatitis, Papulosquamous & Inflammatory Dermatoses 12.2 Acne, Rosacea & Cutaneous Infections 12.3 Herpes Zoster & Autoimmune Blistering Diseases 12.4 Nodules, Tumors & Cutaneous Oncology 12.5 Dermatologic Emergencies & Severe Cutaneous Adverse Reactions 12.6 Pigment Disorders, Alopecia, Nail Disease & Photosensitivity 12.7 Vascular Dermatoses, Environmental Injury & Cutaneous Signs of Systemic Disease
14 Chapter 13: Obstetrics & Gynecology / Women's Health (3% of Exam)
13.1 Contraception, Preconception Care & Teratogenicity 13.2 Hypertensive Disorders of Pregnancy & Gestational Diabetes 13.3 Thyroid Disease & Venous Thromboembolism in Pregnancy 13.4 Menopause & Menopausal Hormone Therapy 13.5 Abnormal Uterine Bleeding, Endometrial Disease & Gynecologic Cancer Screening 13.6 Breast Disorders & Diseases of the Vulva and Vagina 13.7 Menstrual Disorders, Fibroids, Endometriosis & Early Pregnancy Complications
15 Chapter 14: Geriatric Syndromes (3% of Exam)
14.1 Comprehensive Geriatric Assessment & Frailty 14.2 Falls, Gait Assessment & Polypharmacy 14.3 Urinary Incontinence & Pressure Injuries in Older Adults 14.4 Mild Cognitive Impairment, Dementia & Its Subtypes 14.5 Delirium & the Pharmacotherapy of Cognitive Disorders 14.6 Palliative Care, Hospice & Advance Care Planning 14.7 Chronic Wounds, Nutrition, Swallowing, Constipation & Hip Fracture 14.8 Sensory Impairment, Dizziness, Elder Mistreatment & Care Settings
16 Chapter 15: Allergy & Immunology (2% of Exam)
15.1 Anaphylaxis: Recognition & Emergency Management 15.2 Urticaria & Angioedema 15.3 Drug Allergy, Desensitization & Adult Immunodeficiency 15.4 Food Allergy, Insect Venom Hypersensitivity, Serum Sickness & Contrast Reactions 15.5 Rhinitis, Conjunctivitis, Eosinophilic & Mast Cell Disorders
17 Chapter 16: Preventive Medicine, Immunization & Clinical Epidemiology
16.1 The USPSTF Framework & Evidence-Based Cancer Screening 16.2 Cardiovascular & Metabolic Screening and Primary Prevention 16.3 Adult Immunization & Vaccines in Special Populations 16.4 Clinical Epidemiology, Biostatistics & Study Design
18 Chapter 17: Miscellaneous - Ethics, Patient Safety & Quality Improvement (2% of Exam)
17.1 Principles of Bioethics & Decisional Capacity 17.2 Informed Consent, Treatment Refusal & Special Scenarios 17.3 Surrogate Decision-Making, Advance Directives & Confidentiality 17.4 Patient Safety Science, Medical Error & Diagnostic Reasoning 17.5 Quality Improvement Methods, Health Disparities & Health Equity
19 Chapter 18: Perioperative Medicine & Medical Consultation
18.1 Preoperative Cardiovascular Risk Assessment 18.2 Preoperative Pulmonary Risk & Perioperative Medication Management 18.3 Perioperative Anticoagulation, Bridging & Postoperative Complications
20 Chapter 19: Ophthalmology (1% of Exam)
19.1 The Acute Red Eye & Ophthalmic Emergencies 19.2 Painless Vision Loss & Chronic Ophthalmic Disease 19.3 Uveitis, Scleritis & Orbital Disease
21 Chapter 20: Otolaryngology & Dental Medicine (1% of Exam)
20.1 Dizziness, Vertigo & Epistaxis 20.2 Ear Disorders, Hearing Loss & Upper Respiratory Infections 20.3 Oral Cavity, Salivary Gland, Laryngeal & Taste and Smell Disorders
2.3 Thyroid Function Testing & Hypothyroidism
Key Takeaways Explain This Topic AI
The thyroid blueprint subsection enumerates hyperthyroidism, hypothyroidism, thyroiditis, nodules and cancer, euthyroid sick syndrome, thyroid storm, myxedema coma, and thyroid disease in pregnancy.
Subclinical hypothyroidism is an elevated thyroid-stimulating hormone with a normal free thyroxine level and is treated selectively rather than universally.
Levothyroxine requirements rise early in pregnancy, and women with known hypothyroidism need a dose increase as soon as pregnancy is confirmed.
Euthyroid sick syndrome produces a low triiodothyronine level in acutely ill patients and should not be treated with thyroid hormone.
Myxedema coma requires intravenous thyroid hormone plus empiric stress-dose glucocorticoid until coexisting adrenal insufficiency is excluded.
Last updated: August 2026
Thyroid disorders encompass common functional disturbances, life-threatening endocrine emergencies, and structural lesions. This section builds the interpretive framework — how to read a thyroid-stimulating hormone and free thyroxine pair, when that pair is lying, and how to manage hypothyroidism and myxedema coma. Thyrotoxicosis, thyroid storm, thyroiditis, and thyroid nodules and carcinoma are developed in the section that follows.
1. Interpretation of Thyroid Function Test Patterns
Serum TSH (Thyroid-Stimulating Hormone) (normal range: 0.4–4.5 mIU/L) paired with Free T4 (normal range: 0.8–1.8 ng/dL) and Free T3 (normal range: 2.3–4.2 pg/mL) provides the foundation for diagnosis.
Diagnostic Pattern Serum TSH Free T4 Free T3 Clinical Etiologies & Action
Primary Hypothyroidism Elevated (> 4.5) Low (< 0.8) Low or Normal Hashimoto thyroiditis, post-ablative, post-surgical, iodine deficiency
Central (Secondary/Tertiary) Hypothyroidism Low or Inappropriately Normal Low (< 0.8) Low Pituitary adenoma, apoplexy, craniopharyngioma, Sheehan syndrome (Assess full pituitary axis!)
Subclinical Hypothyroidism Elevated (4.5–9.9) Normal Normal Early Hashimoto; treat if TSH >=10, pregnant, symptomatic + anti-TPO (+), or goiter
Primary Hyperthyroidism Suppressed (< 0.01) Elevated Elevated Graves disease, Toxic Multinodular Goiter, Toxic Adenoma
T3 Toxicosis Suppressed (< 0.01) Normal Elevated Early Graves disease, toxic autonomous adenoma
Subclinical Hyperthyroidism Suppressed (< 0.1) Normal Normal Increased risk for AFib and osteoporosis; treat if age >=65 or postmenopausal
Central (Secondary) Hyperthyroidism Elevated or Normal Elevated Elevated TSH-secreting pituitary adenoma (TSHoma) vs Thyroid Hormone Resistance ( THRB mutation)
Euthyroid Sick Syndrome (Non-Thyroidal Illness) Normal or Low Normal or Low Markedly Low (High rT3) Severe systemic illness / ICU; 5'-deiodinase inhibition; Do NOT treat with Levothyroxine
- 2. Hypothyroidism & Myxedema Coma
- Primary Hypothyroidism Etiology & Management
Etiology: Hashimoto thyroiditis (chronic lymphocytic thyroiditis) is the most common cause in iodine-sufficient areas; characterized by circulating anti-thyroperoxidase ( anti-TPO ) antibodies (>90%) and anti-thyroglobulin ( anti-Tg ) antibodies. Other causes include prior radioiodine ablation, total/subtotal thyroidectomy, external neck irradiation, and medications (Amiodarone, Lithium, Sunitinib, Pembrolizumab/Nivolumab checkpoint inhibitors).
Levothyroxine (T4) Dosing:
Young, Healthy Adults: Full replacement dose of 1.6 mcg/kg/day ideal body weight.
Elderly (>=65 yo) or Known Coronary Artery Disease (CAD): Start low at 25–50 mcg/day and titrate gradually by 12.5–25 mcg every 6–8 weeks (avoids precipitating myocardial ischemia, angina, or tachyarrhythmias).
Administration Instructions: Take on an empty stomach with plain water 30–60 minutes before breakfast or at bedtime (>=3–4 hours after dinner). Separate by at least 4 hours from interfering medications: calcium carbonate, ferrous sulfate, aluminum hydroxide antacids, proton pump inhibitors, sucralfate, cholestyramine, and raloxifene.
Monitoring: Recheck serum TSH 6–8 weeks after initiating or changing dose. Once euthyroid, monitor annually.
Pregnancy Requirements: Thyroid binding globulin (TBG) surges in pregnancy. Hypothyroid women must increase levothyroxine by 25–30% (e.g., take 2 extra tablets weekly) immediately upon confirming pregnancy; target trimester-specific TSH (1st trimester < 2.5 mIU/L).
Subclinical Hypothyroidism Indications for Treatment
Treatment with levothyroxine is indicated if:
Serum TSH is >= 10 mIU/L (reduces progression to overt disease, adverse lipid profiles, and cardiovascular mortality).
Patient is pregnant or actively attempting pregnancy.
Serum TSH is between 4.5–9.9 mIU/L WITH positive anti-TPO antibodies , symptomatic overt fatigue/depression, or prominent goiter.
Myxedema Coma: Life-Threatening Decompensation
Clinical Presentation: Severe decompensated hypothyroidism triggered by sepsis, cold exposure, stroke, myocardial infarction, or sedative medications. Classic pentad: Hypothermia (temperature often <35°C / 95°F), Severe Bradycardia , Altered Mental Status / Coma , Hypoventilation (respiratory failure with hypercapnia), and Hyponatremia / Hypoglycemia .
Emergency ICU Protocol:
Stress-Dose Glucocorticoids FIRST: Administer Hydrocortisone 100 mg IV every 8 hours (or Dexamethasone 4 mg IV) immediately BEFORE or concurrently with levothyroxine until secondary adrenal insufficiency is excluded (thyroid hormone replacement accelerates hepatic cortisol clearance, precipitating fatal adrenal crisis if adrenal reserve is compromised).
Intravenous Thyroid Hormone Replacement: IV Levothyroxine (T4) loading dose of 200–400 mcg IV , followed by 50–100 mcg IV daily, plus consideration of IV Liothyronine (T3) 5–20 mcg loading then 2.5–10 mcg q8h (due to impaired peripheral T4-to-T3 conversion in critical illness).
Supportive Care: Mechanical ventilation, passive external rewarming with warm blankets (avoid aggressive active warming which causes vasodilation and circulatory collapse), and cautious IV isotonic crystalloids/hypertonic saline for severe hyponatremia.