Study guide
3.1 Prioritization, Rejection, and Specimen Preparation
ASCP Microbiology Technologist M ASCP
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1 Introduction & Exam Overview
1.1 Current M(ASCP) Exam Facts 1.2 CAT, Scoring, Retakes, and CMP 1.3 Eligibility Routes and Clinical Experience
2 Preanalytic: Collection and Transport
2.1 Patient Identification and Specimen Labeling 2.2 Specimen Collection, Sterile Technique, and Blood Cultures 2.3 Transport Devices, Atmosphere, Time, and Temperature
3 Preanalytic: Processing, Media, and Incubation
3.1 Prioritization, Rejection, and Specimen Preparation 3.2 Media Types, Components, and Selection 3.3 Inoculation, Incubation Conditions, and Slide Preparation
4 Preanalytic: Stains
4.1 Gram Stain: Procedure, Principle, and Interpretation 4.2 Acid-Fast and Modified Acid-Fast Stains 4.3 KOH, Calcofluor-White, Trichrome, Giemsa, and Acridine Orange
5 Bacteriology: Blood and Bone Marrow
5.1 Blood Culture Systems and Rapid Identification 5.2 Bloodstream Pathogens and Skin Flora Significance 5.3 Endocarditis, Bone Marrow Pathogens, and Pathogenicity
6 Bacteriology: CSF and Sterile Body Fluids
6.1 CSF Sources and Acute Meningitis Pathogens 6.2 Shunt Infections, CSF Correlates, Antigen and Molecular Methods 6.3 Sterile Body Fluids: Pathogens, Flora, and Molecular Methods
7 Bacteriology: Respiratory Tract
7.1 Lower Respiratory Specimens, CAP, and HAP Pathogens 7.2 Cystic Fibrosis Pathogens and Quantitative Reporting 7.3 Upper Respiratory: Pharyngitis, Otitis, Sinusitis, Antigen/Molecular
8 Bacteriology: Gastrointestinal Tract
8.1 Enteric Pathogens: Culture and Colony Morphology 8.2 Clostridioides difficile, Shiga Toxin, and Serotyping 8.3 Helicobacter pylori Detection and GI Pathogenicity
9 Bacteriology: Skin, Soft Tissue, and Bone
9.1 Skin, Soft Tissue, and Bone Pathogens 9.2 Bite Wounds and Zoonotic Infections 9.3 SST Pathogenicity and Virulence Mechanisms
10 Bacteriology: Genital Tract and Urine
10.1 Genital Flora and Vaginitis Pathogens 10.2 Neisseria gonorrhoeae, Chlamydia trachomatis, GBS, and Mycoplasma 10.3 Urinary Pathogens, Colony Counts, and Urinalysis Correlation
11 Bacteriology: Identification Methods
11.1 Colony Morphology and Rapid Presumptive Tests 11.2 Conventional Biochemicals and Commercial Kits 11.3 Automated Methods, MALDI-TOF MS, Molecular, and 16S Sequencing
12 Bacteriology: Antimicrobial Susceptibility and Resistance
12.1 Microbroth Dilution, Disk Diffusion, and Gradient Diffusion 12.2 Phenotypic Detection of Resistance 12.3 Antibiotic Classes, Intrinsic Resistance, and Genetic Markers
13 Bacteriology: Resistance Screening and Select Agents
13.1 MRSA/MSSA, VRE, ESBL/CRE Screening 13.2 BSL-3 Pathogens and Select-Agent Presumptive Identification 13.3 Laboratory Response Network and Select-Agent Pathogenicity
14 Mycobacteriology and Nocardia
14.1 Specimens, Major Pathogens, and Disease States 14.2 Acid-Fast Reaction, Colony Morphology, and Growth Characteristics 14.3 Identification Methods, Direct Molecular Detection, and TB Therapy
15 Virology
15.1 Respiratory, Vesicle, Meningitis, and GI Viruses 15.2 Hepatitis, HIV, and Immunocompromised-Host Viruses 15.3 Direct Detection Methods and HPV Cervical Screening
16 Parasitology
16.1 Blood, Tissue, and Brain Protozoa 16.2 Intestinal/Urogenital Protozoa and Helminths 16.3 Microscopy, Antigen/Molecular Detection, Insects and Arthropods
17 Mycology
17.1 Yeasts: Candida, Cryptococcus, and Malassezia 17.2 Dimorphic Fungi and Dermatophytes 17.3 Mucorales, Hyaline Molds, Pneumocystis, and Identification Methods
18 Serology
18.1 Immunoglobulin Response and Antigen-Antibody Methods 18.2 Viral Serodiagnosis: Hepatitis, EBV, HIV, CMV, Rubella, Measles 18.3 Treponema, Borrelia, and TB Infection Serodiagnosis
19 Laboratory Operations: Postanalytic Procedures and Quality
19.1 Documentation, Critical Values, Corrected Reports, and Public Health 19.2 Quality Control, Root-Cause Analysis, and POCT 19.3 Proficiency Testing, Competency, and Accreditation
20 Laboratory Operations: Safety, Mathematics, and Instrumentation
20.1 Biosafety, PPE, Bloodborne Pathogens, and SDS 20.2 Emergencies and Packaging/Transportation of Specimens 20.3 Laboratory Mathematics and Instrumentation
3.1 Prioritization, Rejection, and Specimen Preparation
Key Takeaways Explain This Topic AI
Process CSF, other sterile fluids, and irreplaceable surgical tissues before sputum, urine, stool, and swabs.
Reject unlabeled, leaked, QNS, formalin-fixed-for-culture, dried-swab, and saliva-as-sputum specimens; notify the provider and recollect.
Never process AFB specimens in the same Class II BSC session as routine bacterial cultures.
Use NALC-NaOH digestion and decontamination for contaminated mycobacterial specimens such as sputum, not for sterile fluids.
Mince tissue for fungal culture; grinding can destroy Mucorales hyphae and produce a false-negative mold culture.
Last updated: August 2026
The M(ASCP) processing bench is a triage station, not a conveyor belt. Official outline I.B Specimen Processing sits inside Preanalytic Procedures (10–15%; content guideline revised 2025-09-25) and tests whether you can decide which container is opened first, which container is rejected, how a Class II biosafety cabinet and PPE are used, and which preparation method matches the organism class. A mistake at this step is not repaired by a later Gram stain, MALDI-TOF identification, or a perfect susceptibility panel. After this section, drill the same decisions with free ASCP M practice questions .
Specimen prioritization
CSF is the prototype STAT microbiology specimen. Neisseria meningitidis and Streptococcus pneumoniae die and lose characteristic morphology as the tube sits; neutrophils lyse; and empiric meningitis therapy is rewritten by a smear that should have been stained within minutes of receipt, not after a rack of urines. Other normally sterile fluids—pleural, peritoneal, synovial, pericardial, and vitreous—follow immediately because they are invasive, low-burden, and irreplaceable. Operating-room tissue, transplant biopsies, and neonatal specimens are treated the same way: the incision is already closed or the infant cannot be recollected without harm.
A practical STAT queue
Invasive lower-respiratory specimens (bronchoalveolar lavage, protected specimen brush, bronchial washings) outrank expectorated sputum. They are obtained under sedation or intubation, they support quantitative thresholds used for ventilator-associated pneumonia, and they cannot be casually repeated. Instrument-positive blood-culture bottles are pulled when the continuous-monitoring system alarms; they are already growing and become a laboratory emergency even though the original venipuncture happened hours earlier.
Routine sputum, midstream urine, stool, genital swabs, and surface wound swabs are clinically important but sit later in the queue unless the requisition documents a true emergency such as suspected necrotizing fasciitis (treat that tissue as a sterile-site STAT). A working M-exam order is: (1) CSF and other sterile fluids, (2) tissues and deep aspirates, (3) invasive respiratory specimens, (4) flagging blood-culture bottles, (5) sputum, urine, stool, and swabs. When two STATs arrive together, the specimen that cannot be recollected wins. Do not hide a CSF behind a stack of outpatient urines—the exam writes that sequencing error on purpose.
Rejection criteria
Rejection is a documented patient-safety action, not a scolding of the collector. Notify the authorized provider, explain why a result would be misleading, and request recollection when the patient can still provide material. Unlabeled or mismatched identifiers are an automatic reject. Microbiology requires two unique identifiers that match the requisition; a room number, a first name, or a label from a different patient is not close enough. Leaked or cracked containers are rejected because the exterior contaminates staff and the interior is no longer a closed culture.
Prolonged delay is source-specific. Unpreserved urine held at room temperature longer than about 2 hours overgrows urethral flora and inflates CFU/mL. Stool for culture delayed without Cary-Blair loses Shigella . Anaerobic swabs held in ambient air kill the organisms the clinician wanted. Saliva submitted as sputum is a high-yield reject: numerous squamous epithelial cells and scant neutrophils mean oropharyngeal material that will grow viridans streptococci and saprophytic Neisseria , not the pneumonia pathogen. Quantity not sufficient (QNS) applies when volume cannot cover every ordered test—for example a few drops of CSF when Gram stain, culture, cryptococcal antigen, and multiplex PCR are all requested.
Specimens that are already nonviable
Formalin-fixed tissue is rejected for culture. Formalin kills bacteria, mycobacteria, and fungi; rinsing a histology block does not restore viability. Culture and histopathology must be split in the operating room. Dried swabs are rejected because organisms have already died in the fibers. Do not set up anaerobic culture on voided urine, sputum, stool, or vaginal swabs—those sites either harbor resident anaerobes or are incompatible with anaerobic interpretation. Stool culture from a patient hospitalized more than 3 days is typically cancelled in favor of Clostridioides difficile testing unless a special indication is documented. Duplicate same-source cultures within 24 hours may be rejected by policy. The exam answer is almost never “plate it anyway and add a footnote.”
Biosafety cabinet and PPE
Process respiratory specimens, tissues that may contain dimorphic fungi or mycobacteria, and any rule-out select agent inside a certified Class II biosafety cabinet. Standard PPE is gloves, a fluid-resistant laboratory coat or gown, and eye protection. Add a fit-tested N95 respirator or PAPR for aerosol-generating AFB procedures. Use aerosol-tight centrifuge cups, keep plate lids over agar as shields, and disinfect the cabinet with a mycobactericidal agent after AFB work.
The signature exam trap is processing AFB specimens in the same BSC session as routine bacterial cultures. Mycobacterium tuberculosis aerosols settle onto neighboring blood-agar and chocolate plates and later grow as false-positive TB cultures—patients are isolated and treated for laboratory contamination. Dedicate cabinet time to AFB, process one sediment at a time, keep caps on during vortexing, and never treat the TB hood as extra space for routine sputum plating.
Preparation methods
Concentration increases yield from large-volume, low-burden fluids. CSF and other sterile fluids are centrifuged; the pellet is used for Gram stain, culture, and often molecular testing. Do not discard the supernatant until every ordered assay is accounted for.
Digestion, decontamination, and TB cross-contamination
Digestion and decontamination are mycobacteriology steps for contaminated sites, especially sputum. N-acetyl-L-cysteine (NALC) liquefies mucus by breaking disulfide bonds; sodium hydroxide (NaOH) kills rapidly growing oral bacteria and fungi that would overgrow slow mycobacteria. Contact time is controlled (commonly about 15 minutes with NALC–2% NaOH in CDC-style procedures): too little NaOH leaves contaminants; too much kills mycobacteria. After neutralization and centrifugation, inoculate Lowenstein-Jensen, Middlebrook 7H11, and MGIT and prepare the AFB smear from the same pellet. Do not digest CSF or sterile-field tissue that has no competing flora.
Prevention of TB cross-contamination is a procedure of its own: unidirectional AFB workflow, single-use pipettes, negative processing controls when required, and no batch-opening of multiple sputa in a visible aerosol. Sterile technique on the open bench still matters for routine work—disposable or properly flamed loops, no glove prints on agar, lids held as shields.
Tissue work and molecular extraction
Tissue homogenization is organism-class specific. Bacterial abscess and tissue are often ground to release intracellular organisms. For fungi—especially Mucorales with fragile nonseptate hyphae—mince with a sterile scalpel instead of grinding. Grinding shears hyphae and can produce a false-negative mold culture, the second high-yield trap in this section.
DNA and RNA extraction for molecular microbiology must match the target. RNA viruses need RNase-free handling and reverse transcription; DNA assays still fail when blood, mucin, or residual formalin inhibit polymerase. Include extraction and inhibition controls, and keep molecular workflow unidirectional so amplicons from yesterday’s CSF PCR do not contaminate today’s extract. Do not perform nucleic-acid extraction in the AFB cabinet merely because it is a hood.
- Specimen or problem Processing decision Why the M exam cares
- Unlabeled or mismatched IDs Reject and recollect Result cannot be assigned to a patient
- Leaked or cracked container Reject Interior compromised; exterior is a biohazard
- Saliva labeled as sputum Reject Squamous cells predict mouth flora
- Formalin-fixed tissue for culture Reject Organisms are nonviable
- Dried swab Reject Organisms already dead
- Sputum for AFB NALC-NaOH, then concentrate Liquefy mucus and kill oral flora
- Sterile fluid Concentrate; do not digest No competing flora to kill
- Tissue for fungal culture Mince; do not grind Preserve Mucorales hyphae
- AFB plus routine cultures Separate BSC sessions Stop TB plate contamination
If you can apply that table without hesitation, you have the prioritization, rejection, and preparation cluster that I.B actually scores.