ASCP MLA cheat sheet

CLSI order of draw for venipuncture: blood culture → light-blue sodium citrate → red/gold serum → green heparin → lavender EDTA → gray fluoride-oxalate.

Light-blue 3.2% citrate tubes must be filled to the indicated line to keep the 9:1 blood-to-anticoagulant ratio; a hematocrit above 55% requires reducing the citrate volume.

Tourniquet application longer than 1 minute causes hemoconcentration and falsely elevates potassium, total protein, and lipid results.

EDTA (lavender) is the anticoagulant of choice for hematology because it chelates calcium and preserves red cell and platelet morphology.

Hemolyzed specimens falsely elevate potassium, LDH, AST, and phosphate and are usually rejected for those assays.

Blood cultures: collect 2 sets from separate sites before antimicrobials, disinfect with chlorhexidine gluconate, and obtain 20–30 mL per adult set.

Cold agglutinin and cryoglobulin specimens are clotted and transported at 37°C and separated warm.

Ammonia is collected in EDTA on ice with immediate plasma separation; blood gas specimens are iced and analyzed within 15–30 minutes.

Rejection criteria: unlabeled or mislabeled specimen, wrong tube for the test, gross hemolysis, quantity not sufficient, expired collection device.

Rule of three: in normocytic anemia, Hct (%) ≈ 3 × Hgb (g/dL); a large discrepancy suggests an index error or abnormal RBC morphology.

MCV (fL) = Hct (%) × 10 / RBC (10⁶/µL); MCH (pg) = Hgb × 10 / RBC; MCHC = Hgb × 100 / Hct.

Coagulation pathways: intrinsic = XII, XI, IX, VIII (aPTT); extrinsic = III, VII (PT); common = X, V, II, I.

INR = (patient PT / mean normal PT)^ISI; it standardizes thromboplastin reagents for warfarin monitoring.

Mixing study: correction of a prolonged aPTT indicates factor deficiency; failure to correct indicates an inhibitor such as lupus anticoagulant.

Iron deficiency: low ferritin, high TIBC, low transferrin saturation; anemia of chronic disease: low serum iron, low TIBC, normal or high ferritin.

One platelet per oil-immersion field ≈ 10,000–20,000/µL; 8–20 per field corresponds to the normal 150,000–450,000/µL range.

Corrected reticulocyte % = retic % × (patient Hct / normal Hct); a maturation-factor correction is applied in anemia.

Mentzer index = MCV/RBC: below 13 favors thalassemia trait, above 13 favors iron deficiency anemia.

Beer-Lambert law: A = ε × b × c; absorbance is proportional to concentration only within the validated linear range, typically A 0.1–2.0.

Anion gap = Na − (Cl + HCO3), reference 8–12 mmol/L; add 2.5 mmol/L for each 1 g/dL that albumin is below 4.0.

Corrected calcium = measured Ca + 0.8 × (4.0 − albumin in g/dL).

Friedewald LDL = TC − HDL − TG/5; invalid when triglycerides exceed 400 mg/dL, so use direct LDL or non-HDL cholesterol instead.

Cockcroft-Gault: CrCl (mL/min) = (140 − age) × weight (kg) / (72 × serum creatinine), multiplied by 0.85 for females.

Calculated osmolality = 2Na + glucose/18 + BUN/2.8; an osmolal gap above 10 suggests methanol, ethylene glycol, or isopropanol.

HbA1c reflects mean glycemia over about 2–3 months; estimated average glucose (mg/dL) = 28.7 × A1c% − 46.7.

Cardiac troponin above the assay's 99th percentile upper reference limit with a rising or falling pattern defines acute myocardial injury.

Indirect ion-selective electrode sodium and potassium are falsely low in marked hyperproteinemia or hyperlipidemia (pseudohyponatremia).

Gram stain sequence: crystal violet → Gram iodine → decolorizer (alcohol-acetone) → safranin; gram-negative cells stain pink, gram-positive purple.

MacConkey agar selects gram-negative bacilli; lactose fermenters such as E. coli form pink colonies, non-fermenters remain colorless.

Optochin disk (6 mm) with a zone of 14 mm or more, plus bile solubility, identifies Streptococcus pneumoniae.

Bacitracin 0.04-U disk susceptibility indicates Streptococcus pyogenes (group A); S. agalactiae is resistant and CAMP positive.

Coagulase-positive staphylococci are Staphylococcus aureus; the organism also ferments mannitol salt agar, producing yellow colonies.

Clean-catch urine with ≥10⁵ CFU/mL of a single organism indicates significant bacteriuria; lower counts may be significant in symptomatic or catheterized patients.

CSF evaluation: India ink for encapsulated Cryptococcus, Gram stain and culture, and CSF glucose normally about 60% of the serum value.

Susceptibility testing: Kirby-Bauer disk diffusion on Mueller-Hinton agar interpreted by CLSI zone diameters; MICs by broth dilution or E-test.

Stool pathogens: Salmonella and Shigella on HE or XLD agar; Campylobacter jejuni grows at 42°C in a microaerophilic atmosphere.

Westgard 1-2s is a warning rule only and does not reject the run; 1-3s (one control beyond ±3 SD) rejects for random error.

Westgard 2-2s (two consecutive controls beyond the same ±2 SD) and 4-1s or 10x (four or ten results on one side of the mean) reject for systematic error.

Westgard R-4s: the range between two controls within a run exceeds 4 SD, indicating random error and requiring rejection.

CV (%) = (SD / mean) × 100; it expresses imprecision as a percentage for comparison across methods and analyzers.

Sensitivity = TP/(TP + FN); specificity = TN/(TN + FP); PPV = TP/(TP + FP); NPV = TN/(TN + FN).

Sigma metric = (total allowable error − bias) / CV; ≥6 is world class, 3–4 is marginal, and below 3 is unacceptable.

CLIA categorizes tests as waived, moderate, or high complexity; a certificate of waiver permits only waived testing.

Proficiency testing is required three times per year for regulated analytes; unacceptable results trigger corrective action and root cause analysis.

A delta check compares the current result with the patient's previous value and flags excessive change as possible mislabeling or specimen mix-up.