Medical Laboratory Scientist cheat sheet

ABO reverse grouping uses A1 and B reagent red cells; a discrepancy between forward and reverse typing must be resolved before transfusion (e.g., subgroup, cold agglutinin, or missing antibody).

Rh(D) typing: weak D testing is not required on patients when the laboratory uses anti-D reagents that detect weak D variants; donors must be tested for weak D to avoid immunizing D-negative recipients.

Antibody screen positive: identify with panel cells, determine clinical significance, and crossmatch antigen-negative units; AHG phase detects clinically significant IgG antibodies.

DAT positive with IgG and C3 suggests immune hemolysis; eluate may be needed to identify antibody coating the patient's cells (e.g., in autoimmune hemolytic anemia or delayed hemolytic transfusion reaction).

Emergency release: group O packed RBCs (O-negative for females of childbearing age) and AB or group-specific plasma may be issued before completion of compatibility testing.

Crossmatch incompatibility at immediate spin suggests ABO error; incompatibility at AHG indicates an unexpected antibody; check for clerical error first.

Storage: RBCs 1-6°C for 35-42 days depending on additive; platelets 20-24°C with agitation for 5-7 days; FFP frozen at ≤-18°C for 12 months; thawed FFP used within 24 hours.

Antibody titer for ABO-incompatible transplant or HDFN: IgM anti-A/anti-B titers ≥ 1:128 or 1:256 are often used as thresholds; methods vary by institution.

Anion gap = Na − (Cl + HCO3); reference ~8-12 mmol/L; elevated gap suggests MUDPILES (methanol, uremia, DKA, propylene glycol, isoniazid, lactic acidosis, ethylene glycol, salicylates).

Osmolal gap = measured osmolality − calculated (2Na + glucose/18 + BUN/2.8); gap > 10 suggests unmeasured osmoles such as methanol or ethylene glycol.

Corrected sodium for hyperglycemia: add 1.6 mEq/L to measured Na for every 100 mg/dL glucose above 100 (or multiply by 0.016 × (glucose − 100)).

Friedewald LDL = TC − HDL − TG/5 (valid when TG < 400 mg/dL); use direct LDL or non-HDL when TG is high.

Creatinine clearance (Cockcroft-Gault) = [(140 − age) × weight kg] / (72 × SCr), × 0.85 for females; used for drug dosing.

Cardiac troponin is the preferred biomarker for myocardial injury; hs-cTn with serial 0-1 h or 0-3 h algorithms; CK-MB is no longer first-line.

HbA1c reflects mean glucose over ~120 days; NGSP-certified methods; hemoglobin variants and recent transfusion can interfere.

Lipemia, hemolysis, and icterus (HIL) interfere with spectrophotometric assays; check HIL indices before reporting questionable results.

PT measures the extrinsic and common pathway (factors VII, X, V, II, fibrinogen); INR = (PT patient / PT normal)^ISI, used for warfarin monitoring.

aPTT measures intrinsic and common pathway (factors XII, XI, IX, VIII, X, V, II, fibrinogen); prolonged aPTT with normal PT suggests factor VIII, IX, XI, or XII deficiency or a lupus anticoagulant.

Mixing study: correction (aPTT normalizes) suggests factor deficiency; failure to correct suggests an inhibitor (e.g., lupus anticoagulant, factor VIII inhibitor).

Heparin monitoring: anti-Xa is increasingly used over aPTT for UFH; for LMWH, anti-Xa is the standard because aPTT is insensitive.

D-dimer: high negative predictive value for VTE in low/intermediate pretest probability; elevated in DIC, VTE, pregnancy, surgery, inflammation.

DIC: prolonged PT/aPTT, low fibrinogen, elevated D-dimer, schistocytes, thrombocytopenia; ISTH score ≥ 5 consistent with overt DIC.

Platelet function testing: PFA-100/200 closure times; light transmission aggregometry is the gold standard for inherited platelet disorders.

Direct oral anticoagulants (apixaban, rivaroxaban) prolong PT variably; dabigatran prolongs aPTT; specific calibrated anti-Xa or dilute thrombin time assays are preferred for quantification.

CBC reference ranges vary by age and sex; MCV = (Hct/10) / RBC (in millions/µL) × 10; MCH = Hb/RBC × 10; MCHC = Hb/Hct × 100.

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

Reticulocyte index = (retic % × patient Hct / normal Hct) / maturation factor; elevated indicates hemolysis or blood loss; low indicates marrow failure.

Iron studies: iron deficiency shows low ferritin, low iron, high TIBC, low saturation; anemia of chronic disease shows low iron, low TIBC, normal/high ferritin.

CML: t(9;22) BCR-ABL1; peripheral smear shows left shift with basophilia; JAK2 V617F is common in polycythemia vera, essential thrombocythemia, primary myelofibrosis.

Flow cytometry: CD34 for blasts; CD13/CD33 myeloid; CD19/CD20 B-cell; CD3 T-cell; CD10 CALLA; CD5 co-expression with CD23 in CLL.

Hereditary spherocytosis: EMA binding or osmotic fragility; negative DAT; increased MCHC and RDW; splenomegaly and pigment gallstones.

Sickle cell: HbS on hemoglobin electrophoresis or HPLC; sickling test is screening only; confirm with solubility or genetic testing.

Primary immunodeficiency screening: quantitative immunoglobulins, lymphocyte subsets, neutrophil oxidative burst (DHR) for CGD, and complement CH50 for terminal complement deficiency.

ANA is a screening test with high sensitivity but low specificity; confirm with specific antibodies (anti-dsDNA, anti-Sm, anti-Ro/La, anti-histone) and clinical context.

Anti-dsDNA and anti-Sm are specific for SLE; anti-histone suggests drug-induced lupus; anti-Scl-70 (topoisomerase I) suggests diffuse systemic sclerosis.

Complement: low C3/C4 with normal total hemolytic complement suggests consumption (SLE flare, infection); low CH50 suggests terminal pathway deficiency.

Type I hypersensitivity: IgE-mediated mast cell degranulation; test with specific IgE (ImmunoCAP) or skin prick; tryptase is elevated in anaphylaxis.

Type IV hypersensitivity: T-cell mediated, delayed (48-72 h), e.g., tuberculin skin test, contact dermatitis.

ELISA formats: direct (antigen on solid phase), indirect (antibody detection), sandwich (antigen capture), competitive; false positives from heterophile antibodies can be blocked with HAMA blockers.

Syphilis testing: nontrepidal (RPR, VDRL) for screening and monitoring; treponemal (FTA-ABS, TP-PA, EIA) for confirmation; reverse algorithm starts with treponemal EIA.

CLIA '88 categorizes tests as waived, moderate, or high complexity; laboratories need a CLIA certificate and, for non-waived testing, a laboratory director meeting qualification requirements.

Quality control: run at least two levels of control per day of testing for non-waived tests; evaluate Levey-Jennings charts and Westgard rules (1-2s warning, 1-3s, 2-2s, R-4s, 4-1s, 10x rejection).

Proficiency testing (PT) is required for regulated analytes; failure to participate or repeated failures can result in sanctions; PT results must not be shared between laboratories.

Method validation: accuracy, precision, analytical sensitivity/specificity, reportable range, reference intervals; verification required for FDA-cleared tests before patient reporting.

Personnel requirements: laboratory director, technical supervisor, clinical consultant, general supervisor, testing personnel; qualifications vary by test complexity.

CAP and Joint Commission inspections; CAP accreditation requires biannual inspections and compliance with checklists; TJC focuses on patient safety and environment of care.

Biosafety: BSL-2 for most clinical specimens; BSL-3 for M. tuberculosis culture and highly pathogenic agents; follow OSHA bloodborne pathogens standard.

Cost accounting: direct vs indirect costs; test cost includes reagents, labor, overhead, and quality control; break-even analysis informs test menu decisions.

Gram stain: Gram-positive purple (thick peptidoglycan), Gram-negative pink (thin peptidoglycan, outer membrane); shape and arrangement guide preliminary identification.

Streptococcus classification: beta-hemolytic (Lancefield groups A, B, etc.), alpha-hemolytic (pneumoniae, viridans), gamma (enterococcus, non-hemolytic); bacitracin sensitivity and bile esculin help identify group A and group D.

Staphylococcus aureus: coagulase positive, catalase positive, mannitol fermenter; MRSA detection by cefoxitin disk or mecA/nuc PCR.

Enterobacterales: oxidase negative, glucose fermenters; lactose fermentation on MacConkey; identification by biochemical panels or MALDI-TOF.

Pseudomonas aeruginosa: oxidase positive, non-lactose fermenter, grape-like odor, pyocyanin pigment; intrinsically resistant to many antibiotics.

Blood culture: two sets (aerobic and anaerobic) from separate sites before antibiotics; incubation 5 days; positive bottles Gram stain and subculture immediately.

Mycobacterium tuberculosis: acid-fast bacilli on Ziehl-Neelsen or auramine-rhodamine stain; culture on Löwenstein-Jensen or MGIT liquid; NAAT for rapid detection.

Antimicrobial susceptibility: CLSI or EUCAST breakpoints; disk diffusion (Kirby-Bauer) or MIC methods; report ESBL, CRE, MRSA, VRE as resistance markers.

PCR phases: exponential, linear, plateau; real-time PCR quantifies with Ct values; lower Ct generally indicates higher target concentration.

Sanger sequencing: chain termination with dideoxynucleotides; gold standard for single-gene confirmation; limited throughput.

Next-generation sequencing (NGS): massively parallel; used for panels, exomes, genomes; requires bioinformatics pipeline and orthogonal confirmation for germline variants.

Nucleic acid extraction: silica-based columns or magnetic beads; quality checked by A260/A280 (≈1.8 for DNA, ≈2.0 for RNA) and A260/A230.

Viral load monitoring: HIV-1 RNA, HCV RNA, HBV DNA; used to guide therapy; log10 reductions and limits of detection are method-specific.

Molecular oncology: EGFR, KRAS, BRAF, ALK, ROS1, BRCA1/2; tissue or liquid biopsy (ctDNA); variants classified by ACMG/AMP or tier systems.

Infectious disease NAAT: sensitivity depends on specimen type and timing; false negatives possible early in infection; contamination control with UNG and separate pre/post amplification areas.

Quality: positive and negative controls each run; limit of detection determined by probit analysis; verify reference materials and participate in proficiency testing.

Order of draw (CLSI): blood culture, light blue (citrate), red/gold (serum), green (heparin), lavender (EDTA), pink (EDTA for blood bank), gray (fluoride/oxalate).

Tourniquet application ≤ 1 minute; release before needle removal; prolonged tourniquet causes hemoconcentration and falsely elevated potassium, proteins, and cells.

Venipuncture sites: antecubital fossa (median cubital, cephalic, basilic); avoid areas with IV lines, fistulas, mastectomy, lymphedema, or infection.

Hemolysis causes falsely elevated potassium, LDH, AST, and falsely decreased glucose; avoid excessive suction, small needles, and vigorous mixing.

Capillary collection: warm the site, wipe away first drop, avoid squeezing; used for point-of-care glucose and neonatal screening.

Needle safety: OSHA requires safety-engineered devices and immediate sharps disposal; never recap by hand; report needlesticks immediately.

Patient identification: two identifiers (name and date of birth or medical record number); label tubes at bedside; mislabeled specimens must be rejected.

Blood culture collection: 20-30 mL per set for adults; cleanse skin with chlorhexidine; inoculate aerobic bottle first.

Indications: restrictive RBC transfusion thresholds (Hb 7-8 g/dL) for most stable patients; 1 unit raises Hb by ~1 g/dL in an average adult.

Platelet transfusion: prophylactic for counts < 10,000/µL; < 20,000/µL in some settings; therapeutic for bleeding; 1 apheresis unit raises count by ~30,000-50,000/µL.

Plasma: used for coagulopathy with bleeding or before procedures; dose 10-15 mL/kg; not for volume expansion alone.

Transfusion reactions: acute hemolytic (ABO incompatibility, fever, chills, hemoglobinuria), febrile non-hemolytic (most common), allergic, TRALI, TACO, septic.

Stop transfusion immediately for suspected acute hemolytic reaction; maintain IV access, return unit and tubing to blood bank, send post-transfusion sample and urine.

Irradiated blood: prevents transfusion-associated graft-versus-host disease; indicated for immunocompromised patients, intrauterine transfusion, and directed donations from relatives.

Leukoreduction reduces febrile non-hemolytic reactions, CMV transmission, and HLA alloimmunization; universal leukoreduction is common practice.

Massive transfusion: balanced resuscitation; monitor ionized calcium (citrate toxicity), potassium, and temperature; use massive transfusion protocol with 1:1:1 ratios in trauma.

LIS interfaces use HL7 v2.x messages (ADT, ORM, ORU) or FHIR; result messages include OBX segments with observation values and units.

LOINC codes identify laboratory observations; SNOMED CT codes identify specimens and diagnoses; mapping is required for interoperability.

Digital pathology: whole-slide imaging; validation of scanners and displays; AI-assisted algorithms are regulated as medical devices (FDA clearance).

Barcode and RFID tracking improve specimen chain of custody; two-dimensional barcodes increase data capacity and reduce labeling errors.

Data security: HIPAA requires encryption, access controls, audit trails, and minimum necessary access; breach notification rules apply.

Laboratory dashboards: turn-around time (TAT), specimen rejection rates, critical value reporting, and quality metrics; monitor with statistical process control.

Middleware rules route results, add reflex testing, and apply delta checks; rules must be validated and documented.

Interface validation: test with representative messages, verify units, reference ranges, and flags; maintain interface change control and downtime procedures.