Cambodia Laboratory Exit Exam flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Anion gap formula

Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻). Normal range 8–12 mmol/L without potassium. Elevated gap suggests metabolic acidosis from unmeasured anions such as lactate, ketones, or toxins.

HbA1c IFCC conversion

IFCC (mmol/mol) = (NGSP % − 2.15) × 10.929. NGSP % = (IFCC / 10.929) + 2.15. Used to harmonize glycated hemoglobin results across laboratories.

Friedewald LDL formula

LDL-C = total cholesterol − HDL-C − (triglycerides/5). Valid only when triglycerides are below 400 mg/dL; otherwise use direct LDL or non-HDL cholesterol.

Osmolal gap

Measured osmolality minus calculated osmolality (2Na⁺ + glucose/18 + BUN/2.8). Normal gap is less than 10 mOsm/kg; elevated gap suggests ingestion of methanol, ethylene glycol, or isopropanol.

MCV anemia classification

Microcytic anemia: MCV below 80 fL (iron deficiency, thalassemia, chronic disease). Normocytic: 80–100 fL. Macrocytic: above 100 fL (B12/folate deficiency, alcohol, hypothyroidism).

ABO compatibility rule

Group O red cells are universal donor; group AB is universal recipient. For plasma, AB is universal donor and O is universal recipient because isohemagglutinins are reversed.

Platelet transfusion thresholds

Prophylactic transfusion at <10 ×10⁹/L; <20 ×10⁹/L if febrile; <50 ×10⁹/L before invasive procedures; <100 ×10⁹/L for CNS or ocular surgery.

RhIG administration

RhD-negative mothers receive anti-D immunoglobulin 300 µg intramuscularly within 72 hours of delivery or sensitizing event to prevent hemolytic disease of the newborn.

Gram stain decolorization

Decolorize with 95% ethanol for 5–10 seconds. Gram-positive cells retain crystal violet-iodine complex (purple); Gram-negative cells lose stain and take safranin counterstain (pink).

Staphylococcus aureus identification

Catalase positive, coagulase positive, ferments mannitol on mannitol salt agar (yellow colonies). Coagulase positivity distinguishes S. aureus from coagulase-negative staphylococci.

HIV diagnostic algorithm

Fourth-generation ELISA detects p24 antigen and antibody. Reactive samples confirmed by Western blot or HIV-1/2 differentiation immunoassay. Viral load by RT-PCR monitors treatment.

Hepatitis B serology markers

HBsAg indicates infection; anti-HBs indicates immunity; HBeAg indicates high infectivity; anti-HBc IgM indicates acute infection. Interpret all markers together.

Malaria thick and thin films

Thick film detects parasites with higher sensitivity; thin film identifies species by morphology. Giemsa stain at pH 7.2; ring forms and gametocytes suggest P. falciparum.

Schistosoma egg morphology

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

Entamoeba histolytica cysts

Cysts have four nuclei and chromatoid bars; trophozoites may ingest red blood cells. Differentiate from E. coli cysts, which have eight nuclei and do not ingest RBCs.

Dengue vector mosquito

Aedes aegypti is the principal vector, a day-biting mosquito breeding in clean stagnant water. It has lyre-shaped markings on the thorax and banded legs.

Sandwich ELISA principle

Capture antibody binds antigen; detection antibody conjugated to enzyme binds a different epitope. Substrate produces color proportional to antigen concentration. Used for antigens such as HBsAg.

Widal test interpretation

Detects agglutinins against O (somatic) and H (flagellar) antigens of Salmonella Typhi. Paired sera showing a fourfold rise in titer are more informative than a single result.

RPR prozone phenomenon

High antibody titers can cause false-negative non-treponemal tests such as RPR. Dilute the sample and retest to detect the prozone effect.

Complement consumption in SLE

Active systemic lupus erythematosus consumes complement, lowering C3 and C4 and reducing CH50. Serial complement levels help monitor disease activity.

Westgard 1-3s rule

Reject a run when a control value exceeds mean ±3 SD. This indicates random error; investigate and repeat the run before reporting patient results.

Biosafety level 3

BSL-3 is for serious aerosol-transmitted pathogens such as Mycobacterium tuberculosis. Requires directional airflow, sealed room, and respiratory protection for staff.

Autoclave sterilization parameters

Sterilize biological waste at 121°C, 15 psi for 30 minutes. Monitor with biological indicators (Geobacillus stearothermophilus spores) and chemical indicators.

HIV post-exposure prophylaxis

Start antiretroviral prophylaxis within 2 hours of exposure, maximum 72 hours. Continue for 28 days; test baseline and follow-up for HIV seroconversion.

Beer-Lambert law

Absorbance A = ε × c × l, where ε is molar absorptivity, c is concentration, and l is path length (1 cm). Absorbance is proportional to concentration at a fixed wavelength.

Relative centrifugal force

RCF = 1.118 × 10⁻⁵ × r (cm) × (rpm)². Balance tubes by weight and use the correct rotor and speed to separate blood components without hemolysis.

Analytical specificity

Specificity = true negatives / (true negatives + false positives). It is the ability of a test to correctly identify those without the condition.

PCR cycle temperatures

Denaturation at 94–95°C, annealing at 50–65°C, extension at 72°C, for 30–40 cycles. Separate pre- and post-amplification areas prevent contamination.

Epidemic curve interpretation

Plot cases by date of onset. A single peak suggests point source; a plateau suggests continuous common source; successive peaks suggest propagated spread.

Notifiable disease reporting

Laboratories must report suspected or confirmed cases of specified diseases to the national surveillance authority within mandated timeframes, such as immediately for cholera.

Informed consent elements

Provide purpose, risks, benefits, alternatives, and right to refuse. Document consent for invasive procedures and research; use interpreter services when needed.

Critical result communication

Report immediately to the responsible clinician, document time, recipient, and read-back of the result. Critical values require timely communication to ensure patient safety.