Updated for 2026
MLT exam prep: clinical chemistry, haematology, microbiology, and laboratory sciences
The Medical Laboratory Technician (MLT) certification examination tests competency across all major laboratory disciplines. ASCP Board of Certification and AMT/AMTIE MLT exams cover clinical chemistry, haematology, coagulation, microbiology, blood banking/immunohaematology, body fluids, urinalysis, and laboratory operations and safety.
Educational purpose: This content is for exam preparation and professional development only. It is not intended for clinical decision-making. Always follow current guidelines, institutional policies, and scope of practice.
Clinical chemistry — reference ranges and critical values
Glucose: Fasting reference 70–99 mg/dL. Critical low <40–50 mg/dL (hypoglycaemia); critical high >500 mg/dL (DKA/HHS). Glucose tolerance: 2-hour post-OGTT normal <140; IGT 140–199; diabetes ≥200 mg/dL.
Electrolytes — critical values: Na+ (normal 136–145 mEq/L): critical <120 or >160 mEq/L. K+ (3.5–5.0): critical <2.5 or >6.5 mEq/L (cardiac arrhythmia risk). Ca²⁺ total (8.5–10.5 mg/dL): critical <6.0 or >13 mg/dL. CO₂ (bicarbonate 22–29): critical <10 or >40 mEq/L.
Renal function: Creatinine: males 0.7–1.3, females 0.6–1.1 mg/dL. BUN: 7–25 mg/dL. BUN:creatinine ratio: normal 10:1–20:1; >20:1 suggests prerenal azotaemia; <10:1 suggests intrinsic renal disease or liver disease. eGFR calculation uses MDRD or CKD-EPI equations.
Cardiac markers: Troponin I/T: highly specific for myocardial injury. Rises 3–4 hours post-MI, peaks 12–24 hours, normalises 7–14 days (I) or 10–14 days (T). High-sensitivity troponin improves early diagnosis. BNP: >100 pg/mL suggests HF; NT-proBNP >300 pg/mL suggests acute decompensated HF (age-adjusted thresholds).
Thyroid function: TSH: 0.4–4.5 mIU/L (most sensitive for thyroid dysfunction). Free T4: 0.8–1.8 ng/dL. Free T3: 2.3–4.2 pg/mL. TSH low + free T4 high = hyperthyroidism. TSH high + free T4 low = hypothyroidism. TSH normal with symptoms = rule out non-thyroidal illness.
Haematology and coagulation
CBC reference ranges (adults): WBC: 4.5–11.0 × 10³/μL. RBC: males 4.7–6.1, females 4.2–5.4 × 10⁶/μL. Haemoglobin: males 14–18, females 12–16 g/dL. Haematocrit: males 42–52%, females 37–47%. MCV: 80–100 fL. MCH: 27–33 pg. Platelets: 150–400 × 10³/μL.
Anaemia classification by MCV: Microcytic (MCV <80): Iron deficiency (most common worldwide), thalassaemia, anaemia of chronic disease (usually normocytic). Normocytic (MCV 80–100): Acute blood loss, haemolysis, anaemia of chronic disease, renal failure, mixed deficiency. Macrocytic (MCV >100): B12/folate deficiency, liver disease, hypothyroidism, medications (methotrexate, hydroxyurea, zidovudine).
Coagulation cascade: PT (prothrombin time) tests extrinsic pathway (factor VII) + common pathway (X, V, II, I). INR = PT/control — used for warfarin monitoring. PTT tests intrinsic pathway (XII, XI, IX, VIII) + common. Prolonged PT only: factor VII deficiency or warfarin. Prolonged PTT only: haemophilia A/B, von Willebrand disease, heparin. Prolonged both: DIC, liver disease, vitamin K deficiency, common pathway defects.
Microbiology — Gram stain, culture, and antibiotic susceptibility
Gram stain interpretation: Gram-positive organisms retain crystal violet (purple). Gram-negative organisms lose crystal violet and pick up safranin counterstain (pink/red). Key pathogens: Gram+ cocci in clusters = Staphylococcus. Gram+ cocci in chains/pairs = Streptococcus/Enterococcus. Gram+ rods = Clostridium, Bacillus, Corynebacterium, Listeria. Gram- rods = Enterobacteriaceae (E. coli, Klebsiella, Pseudomonas). Gram- diplococci = Neisseria.
Culture media and growth: Blood agar: non-selective; haemolysis patterns (alpha = greenish/partial, beta = clear/complete lysis — S. pyogenes, S. aureus, gamma = no lysis). MacConkey agar: selective for Gram-negative enteric bacteria; differentiates lactose fermenters (pink — E. coli, Klebsiella) from non-fermenters (colourless — Salmonella, Shigella, Pseudomonas). Mannitol salt agar: selective for Staphylococcus; S. aureus ferments mannitol (yellow halo).
Antimicrobial susceptibility testing (AST): Kirby-Bauer disc diffusion: inhibition zone diameter compared to CLSI breakpoints — susceptible (S), intermediate (I), resistant (R). MIC (minimum inhibitory concentration): dilution method; required for serious infections and for β-lactam resistance determination.
Frequently asked questions
- What are the most important critical values that an MLT must immediately report to the ordering provider?
- Critical values represent life-threatening laboratory results requiring immediate clinical action. Each laboratory establishes its own critical value list per accreditation requirements (CAP, JCAHO). Common critical values: Glucose <40 or >500 mg/dL; Potassium <2.5 or >6.5 mEq/L; Sodium <120 or >160 mEq/L; Calcium <6.0 or >13 mg/dL; Haemoglobin <7 g/dL or a precipitous drop; Platelet count <20,000/μL; INR >5.0; PTT >100 seconds; Troponin any elevation (first positive); PO₂ <40 mmHg. The MLT must document: time result verified, time provider notified, name of person notified, and result repeated back and confirmed. Failure to report critical values is a patient safety event and a regulatory compliance violation.
Clinically reviewed by NurseNest Clinical Review Team · Last updated 2026-06-10 · For educational purposes only · Review policy