Cambodia Laboratory Exit Exam cheat sheet

Reference interval for fasting plasma glucose in adults is typically 70–99 mg/dL (3.9–5.5 mmol/L); impaired fasting glucose 100–125 mg/dL; diabetes ≥126 mg/dL on two occasions.

Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻); normal 8–12 mmol/L (without K⁺). High anion gap metabolic acidosis: MUDPILES (methanol, uremia, DKA, propylene glycol, isoniazid, lactic acidosis, ethylene glycol, salicylates).

Serum creatinine reflects glomerular filtration; eGFR (CKD-EPI) = 141 × min(Scr/κ,1)^α × max(Scr/κ,1)^−1.209 × 0.993^Age × 1.018 [if female], where κ=0.7 (female) or 0.9 (male), α=−0.329 (female) or −0.411 (male).

Enzymatic assays: ALT and AST use NADH oxidation measured at 340 nm; hemolysis falsely elevates AST and LD, while EDTA contamination falsely lowers calcium and raises potassium.

Cardiac troponin I or T is the preferred biomarker for myocardial infarction; serial sampling with high-sensitivity assays detects a rise/fall pattern with at least one value above the 99th percentile upper reference limit.

HbA1c reflects average glycemia over ~120 days; NGSP/IFCC standardization: IFCC (mmol/mol) = (NGSP % − 2.15) × 10.929. Hemoglobinopathies and recent transfusion invalidate results.

Lipid targets: LDL-C <100 mg/dL for high-risk, <70 mg/dL for very high-risk patients; Friedewald formula LDL = TC − HDL − (TG/5) is invalid when TG >400 mg/dL.

Bilirubin measurement by diazo reaction (Jendrassik-Grof); direct (conjugated) bilirubin reacts without accelerator, indirect requires alcohol or caffeine accelerator.

Osmolality (mOsm/kg) = 2Na⁺ + glucose/18 + BUN/2.8; measured osmolality minus calculated = osmolal gap, normal <10 mOsm/kg.

Complete blood count reference (adult): Hb 13–17 g/dL (male), 12–15 g/dL (female); MCV 80–100 fL; platelets 150–450 ×10⁹/L; WBC 4–11 ×10⁹/L.

Anemia classification by MCV: microcytic <80 fL (iron deficiency, thalassemia, anemia of chronic disease), normocytic 80–100 fL, macrocytic >100 fL (B12/folate deficiency, alcohol, hypothyroidism).

Iron studies: ferritin is the most sensitive marker of iron deficiency; transferrin saturation <20% and elevated TIBC suggest iron deficiency, while ferritin >100 µg/L with low TIBC suggests anemia of chronic disease.

ABO compatibility: group O is universal donor for red cells; group AB is universal recipient. Plasma compatibility is reversed: AB plasma is universal donor, O plasma universal recipient.

Crossmatch: immediate spin (IS) detects ABO incompatibility; antihuman globulin (AHG) phase detects IgG and complement-binding antibodies. Antibody screen uses three-cell panel at IS, 37°C, and AHG.

RhD negative recipients must receive RhD negative red cells; RhIG (anti-D) 300 µg IM within 72 hours of delivery or sensitizing event for RhD-negative mothers.

Platelet transfusion threshold: <10 ×10⁹/L prophylactically; <20 ×10⁹/L if febrile; <50 ×10⁹/L before invasive procedure; <100 ×10⁹/L for CNS or ocular surgery.

Sickle cell screen: sodium metabisulfite or solubility test; confirm with hemoglobin electrophoresis (HbS migration pattern) or HPLC.

Coagulation: PT 11–13.5 s, INR 0.8–1.2; APTT 25–35 s. Prolonged PT with normal APTT suggests factor VII deficiency or warfarin effect; both prolonged suggests common pathway defect (factors X, V, II, fibrinogen).

Gram stain: crystal violet 1 min, iodine 1 min, decolorize with 95% ethanol 5–10 s, counterstain safranin 30 s. Gram-positive retain purple; Gram-negative appear pink.

Culture media: MacConkey agar selects Gram-negative bacilli and differentiates lactose fermenters (pink) from non-fermenters (colorless); blood agar supports fastidious organisms and hemolysis patterns.

Staphylococcus aureus: catalase positive, coagulase positive, mannitol fermenter on MSA; Streptococcus pyogenes: bacitracin sensitive, PYR positive; Streptococcus agalactiae: hippurate positive, CAMP test positive.

Mycobacterium tuberculosis: acid-fast bacilli (Ziehl-Neelsen or auramine-rhodamine fluorescence); culture on Löwenstein-Jensen medium at 37°C for 4–8 weeks; GeneXpert MTB/RIF detects rifampicin resistance.

HIV diagnosis: fourth-generation ELISA (p24 antigen + antibody) screening; reactive results confirmed by Western blot or HIV-1/2 differentiation immunoassay; viral load by RT-PCR for monitoring.

Hepatitis B serology: HBsAg indicates infection; anti-HBs indicates immunity; HBeAg indicates high infectivity; anti-HBc IgM indicates acute infection.

Fungal diagnosis: KOH mount for dermatophytes; India ink for Cryptococcus neoformans (encapsulated yeast); germ tube test for Candida albicans; Sabouraud dextrose agar at 25–30°C.

Antimicrobial susceptibility testing: Kirby-Bauer disk diffusion on Mueller-Hinton agar; zone diameters interpreted per CLSI/EUCAST tables; MIC by broth microdilution or E-test.

Dengue: NS1 antigen detectable days 1–5; IgM antibody from day 5; IgG indicates past infection or secondary infection. RT-PCR detects viral RNA in first 5 days.

Malaria diagnosis: thick film for detection (higher sensitivity), thin film for species identification; Giemsa stain at pH 7.2; ring forms and gametocytes of Plasmodium falciparum; Schüffner dots in P. vivax.

Rapid diagnostic tests for malaria detect HRP-2 (P. falciparum) or pLDH (pan-species); HRP-2 persists up to 4 weeks after treatment, causing false positives.

Stool examination: direct wet mount with saline and iodine; formol-ether concentration increases sensitivity for cysts and eggs; modified acid-fast stain for Cryptosporidium and Cyclospora.

Entamoeba histolytica: trophozoites with ingested red cells; cysts with 4 nuclei and chromatoid bars; differentiate from E. coli (8 nuclei, no RBC ingestion).

Soil-transmitted helminths: Ascaris lumbricoides (fertilized eggs, mammillated), Trichuris trichiura (barrel-shaped eggs with bipolar plugs), hookworm (thin-shelled oval eggs).

Schistosoma: S. mansoni eggs have lateral spine; S. haematobium eggs have terminal spine; S. japonicum eggs are round with small lateral spine. Diagnosis by urine or stool sedimentation.

Filaria: Wuchereria bancrofti microfilariae in blood; nocturnal periodicity; diagnosis by thick blood smear or membrane filtration; vector Culex mosquito.

Dengue vector: Aedes aegypti, day-biting, breeds in clean stagnant water; distinguished by lyre-shaped markings on thorax and banded legs.

Scabies: Sarcoptes scabiei; diagnosis by skin scraping with mineral oil, microscopic identification of mites, eggs, or scybala.

ELISA principles: direct, indirect, sandwich, competitive. Sandwich ELISA uses capture antibody and detection antibody; indirect detects patient antibody with enzyme-labeled anti-human globulin.

Widal test for typhoid: detects agglutinins against O (somatic) and H (flagellar) antigens; paired sera showing fourfold rise in titer are more informative than a single titer.

Rheumatoid factor (RF) is an autoantibody (usually IgM) against Fc portion of IgG; anti-CCP is more specific for rheumatoid arthritis.

Antinuclear antibody (ANA) by immunofluorescence on HEp-2 cells; patterns include homogeneous (anti-dsDNA), speckled (anti-Sm, anti-RNP), nucleolar (anti-Scl-70).

Complement: C3 and C4 decreased in active SLE (consumption); CH50 measures classical pathway function.

Syphilis serology: non-treponemal tests (RPR, VDRL) for screening and monitoring; treponemal tests (TPHA, FTA-ABS, EIA) for confirmation. Prozone phenomenon causes false-negative RPR in high antibody titers.

Hepatitis C: anti-HCV screening by EIA; confirm with HCV RNA PCR; window period 4–10 weeks.

Immunodeficiency screening: quantitative immunoglobulins (IgG, IgA, IgM), lymphocyte subsets by flow cytometry (CD4, CD8), and delayed-type hypersensitivity skin tests.

Quality management system (QMS) essentials: document control, competency assessment, equipment maintenance, internal quality control (IQC), external quality assessment (EQA), and corrective/preventive action (CAPA).

Turnaround time (TAT) = report time − order/collection time; monitor median and 90th percentile; define acceptable TAT per test (e.g., stat glucose ≤60 min).

Cost per test = (total direct costs + allocated indirect costs) / number of tests; include reagents, controls, calibrators, labor, equipment depreciation, and overhead.

Staffing plan based on workload: number of tests per technologist per shift; use workload units (e.g., College of American Pathologists workload units) to estimate staffing.

Inventory control: reorder point = (average daily usage × lead time) + safety stock; safety stock = z × standard deviation of demand × √lead time.

Laboratory information system (LIS) validation: user requirements, installation qualification (IQ), operational qualification (OQ), performance qualification (PQ), and change control.

Risk management: failure mode and effects analysis (FMEA) to prioritize risks; severity × occurrence × detection = risk priority number (RPN).

Accreditation standards: ISO 15189 for medical laboratories; ISO 17025 for testing and calibration; CLIA in the United States; national requirements in Cambodia.

Staff competency: initial assessment before independent work, annual review, and reassessment after prolonged absence or policy change.

Internal quality control (IQC): run at least two levels (normal and abnormal) daily or per shift; Westgard rules (1-2s warning, 1-3s rejection, 2-2s rejection, R-4s rejection, 4-1s rejection, 10x rejection).

Levey-Jennings chart plots control values over time with mean ±1, 2, 3 SD; trends (6 consecutive on one side) and shifts indicate systematic error.

External quality assessment (EQA): proficiency testing panels; unacceptable results require root cause analysis and corrective action; participation is mandatory for accreditation.

Biosafety levels: BSL-1 non-pathogenic; BSL-2 moderate risk (most clinical labs); BSL-3 serious aerosol-transmitted pathogens (M. tuberculosis); BSL-4 dangerous exotic agents.

Standard precautions: hand hygiene, gloves, gown, mask, eye protection; sharps disposal in puncture-resistant containers; no recapping of needles.

Spill management: absorb with paper towels, apply 10% bleach (0.5% sodium hypochlorite) for 10 minutes, then wipe; for large spills, evacuate and ventilate.

Biological waste: autoclave at 121°C, 15 psi for 30 minutes; chemical disinfection with 1% sodium hypochlorite for blood spills; incineration for sharps.

Post-exposure prophylaxis: HIV-start antiretroviral within 2 hours (max 72 hours); HBV-vaccine and HBIG if non-immune; HCV-monitor RNA at 4–6 weeks.

Quality indicators: sample rejection rate, turnaround time compliance, critical value reporting, EQA performance, and incident reporting.

Spectrophotometry: Beer-Lambert law A = ε × c × l; absorbance proportional to concentration; measure at wavelength of maximum absorption; cuvette path length 1 cm.

Centrifugation: relative centrifugal force (RCF) = 1.118 × 10⁻⁵ × r (cm) × (rpm)²; balance tubes by weight; use appropriate rotor and speed for cell separation.

Pipetting: use calibrated pipettes; forward pipetting for aqueous solutions; reverse pipetting for viscous or volatile liquids; avoid touching tip to container walls.

Microscopy: Köhler illumination; oil immersion objective (100×) with immersion oil; resolution d = 0.61λ/NA; numerical aperture determines light-gathering and resolving power.

Analytical sensitivity = true positives / (true positives + false negatives); specificity = true negatives / (true negatives + false positives); positive predictive value depends on prevalence.

Precision vs accuracy: precision is closeness of repeated measurements (CV%); accuracy is closeness to true value (bias).

Calibration: use calibrators with assigned values traceable to reference material; verify with independent control materials; recalibrate after major maintenance or lot change.

Point-of-care testing (POCT): validate device, train operators, perform IQC, and document results; connectivity to LIS for result transmission.

PCR: denaturation 94–95°C, annealing 50–65°C, extension 72°C; 30–40 cycles; contamination control with uracil-N-glycosylase and separate pre/post amplification areas.

Notifiable disease reporting: clinicians and laboratories must report suspected or confirmed cases to national surveillance authority within specified timeframes (e.g., immediately for cholera, within 24 hours for measles).

Outbreak investigation steps: verify diagnosis, establish case definition, identify cases, describe time/place/person, formulate hypothesis, test hypothesis, implement control, communicate.

Surveillance types: passive (routine reporting), active (health worker solicits cases), sentinel (selected sites), syndromic (based on symptoms), and laboratory-based.

Epidemic curve: plot cases by date of onset; interpret point source (single peak), continuous common source (plateau), or propagated (successive peaks).

Sensitivity of surveillance = detected cases / true cases; positive predictive value = true cases / reported cases.

Antimicrobial resistance surveillance: collect isolates, perform AST by CLSI/EUCAST, report to national AMR network; use WHONET software.

Water quality testing: thermotolerant coliforms (E. coli) indicate fecal contamination; membrane filtration or multiple tube fermentation; WHO guideline: 0 CFU/100 mL for drinking water.

Foodborne outbreak: collect food, water, and clinical specimens; use pulsed-field gel electrophoresis (PFGE) or whole-genome sequencing for strain typing.

HIV viral load and early infant diagnosis: dried blood spot (DBS) testing for HIV DNA in infants <18 months; viral load monitoring for treatment failure.

Informed consent: patient must receive information on purpose, risks, benefits, alternatives, and right to refuse; document consent for invasive procedures and research.

Confidentiality: patient information must not be disclosed without consent except when required by law (e.g., notifiable diseases) or to prevent serious harm.

Laboratory errors: disclose harmful errors to patients and families; follow institutional incident reporting; maintain transparency and documentation.

Professional boundaries: avoid conflicts of interest; do not accept gifts that influence judgment; maintain competence through continuing education.

Cambodian health law: Ministry of Health regulates laboratory practice; laboratories must be licensed; staff must hold recognized qualifications.

Patient rights: respect autonomy, dignity, privacy, and non-discrimination; provide interpreter services when needed.

Research ethics: institutional review board (IRB) approval; informed consent; risk minimization; data privacy; equitable selection of participants.

Communication of critical results: report immediately to responsible clinician; document time, recipient, and read-back of result.

Whistleblowing: report unsafe practices or unethical conduct to appropriate authority; protect confidentiality of reporter.