MLT cheat sheet

ABO: group A has A antigen and anti-B; group B has B antigen and anti-A; group O has neither antigen and both antibodies; group AB has both antigens and no isohemagglutinins.

Rh D is the most immunogenic red cell antigen; a D-negative result on initial testing requires weak D testing to detect variant D expression.

Antibody screening uses the indirect antiglobulin test to detect clinically significant IgG antibodies; immediate-spin testing primarily detects IgM ABO antibodies.

Crossmatch: immediate spin or room-temperature phase checks ABO compatibility; antiglobulin phase detects clinically significant IgG antibodies.

DAT detects IgG or complement bound to red cells in vivo; an eluate is used to identify antibody coating the patient's red cells.

RBCs are stored at 1-6 C for 35-42 days depending on the additive; FFP is stored at -18 C or colder for up to 12 months; platelets are stored at 20-24 C with agitation for 5-7 days.

Febrile nonhemolytic reaction is the most common transfusion reaction; acute hemolytic reaction is usually caused by ABO incompatibility from clerical error.

IgG antibodies cross the placenta and can cause hemolytic disease of the newborn; IgM antibodies do not cross the placenta efficiently.

Beer-Lambert law: absorbance = molar absorptivity × path length × concentration; absorbance is directly proportional to analyte concentration at a fixed path length.

Fasting plasma glucose reference is about 70-99 mg/dL; enzymatic methods use hexokinase or glucose oxidase.

HbA1c reflects average blood glucose over approximately 2-3 months through nonenzymatic glycation of hemoglobin.

Creatinine is commonly measured by the Jaffe reaction with alkaline picrate; enzymatic creatinine methods are more specific.

Electrolyte reference values: sodium 135-145 mmol/L, potassium 3.5-5.0 mmol/L, chloride 98-107 mmol/L, bicarbonate 22-29 mmol/L.

Anion gap = Na - (Cl + HCO3); reference is about 8-12 mmol/L when potassium is excluded.

Cardiac troponin I and T are the most specific routine markers of myocardial injury and rise within about 3-6 hours after injury.

Friedewald LDL = total cholesterol - HDL - (triglycerides/5); the calculation is unreliable when triglycerides exceed 400 mg/dL.

ALT is more liver-specific than AST; ALP and GGT are used to evaluate cholestatic patterns.

Hemoglobin reference is approximately 13.5-17.5 g/dL for adult males and 12.0-15.5 g/dL for adult females; hematocrit is roughly three times hemoglobin.

MCV = (hematocrit/RBC count) × 10; MCH = (hemoglobin/RBC count) × 10; MCHC = (hemoglobin/hematocrit) × 100.

RDW measures red cell size variation; an elevated RDW indicates anisocytosis and is common in iron deficiency and mixed anemias.

Corrected reticulocyte count = reticulocyte percentage × (patient hematocrit/normal hematocrit); it adjusts the marrow response for anemia severity.

Platelet reference is approximately 150-450 × 10^9/L; platelets are counted by impedance or optical methods.

PT/INR monitors warfarin therapy; aPTT monitors unfractionated heparin therapy.

Iron deficiency anemia shows low ferritin, low serum iron, high TIBC, microcytic hypochromic red cells, and elevated RDW.

Megaloblastic anemia shows elevated MCV, hypersegmented neutrophils, and low vitamin B12 or folate.

Sickle cell screening uses solubility testing; hemoglobin electrophoresis or HPLC confirms hemoglobin S and distinguishes trait from disease.

Gram stain: crystal violet stains all cells; iodine fixes the dye; alcohol-acetone decolorizes gram-negative cells; safranin counterstains gram-negative organisms pink.

Catalase is positive in staphylococci and negative in streptococci; coagulase positivity identifies Staphylococcus aureus.

Streptococcus pyogenes is group A and bacitracin sensitive; Streptococcus agalactiae is group B and CAMP positive.

On MacConkey agar, lactose-fermenting gram-negative bacilli form pink colonies; non-lactose fermenters remain colorless or pale.

Pseudomonas aeruginosa is oxidase positive; Enterobacteriaceae are oxidase negative.

MRSA is detected by cefoxitin resistance and is mediated by the mecA gene.

Adult blood cultures: obtain two or more sets from separate sites, usually 20-30 mL total, before antibiotics; routine incubation is about five days.

Ziehl-Neelsen acid-fast staining uses carbolfuchsin; mycobacteria retain the red stain after acid-alcohol decolorization.

Urine culture colony count of at least 10^5 CFU/mL of a single organism is traditionally considered significant; mixed flora suggests contamination.

Urine specific gravity reference is about 1.005-1.030 and reflects solute concentration; refractometry measures refractive index.

Urine pH reference is about 4.5-8.0; reagent strip pH uses methyl red and bromthymol blue indicators.

Reagent strip protein uses the protein error of a tetrabromophenol blue indicator and is most sensitive to albumin.

Glucose reagent strip uses glucose oxidase and peroxidase; ketone reagent strip uses the nitroprusside reaction.

Leukocyte esterase detects neutrophil esterases, and nitrite detects nitrate-reducing bacteria; both support a urinary tract infection screen.

Microscopy: 0-2 RBC/hpf and 0-5 WBC/hpf are typical; hyaline casts can be normal, RBC casts indicate glomerular bleeding, and WBC casts indicate pyelonephritis.

Normal CSF glucose is about 60% of simultaneous serum glucose, typically 40-70 mg/dL; normal CSF protein is about 15-45 mg/dL.

Seminal fluid reference: volume at least 1.5 mL, sperm concentration at least 15 million/mL, and motility at least 40%.

Primary immune response produces mainly IgM after a lag; secondary response produces mainly IgG with higher titer and faster onset.

IgG is the most abundant immunoglobulin and the only one that crosses the placenta efficiently; IgM is a pentamer and is primarily intravascular.

Complement classical pathway begins with C1q binding to antigen-antibody complexes; alternative and lectin pathways activate without C1.

Sandwich ELISA captures antigen with a solid-phase antibody and detects it with an enzyme-labeled second antibody; color is proportional to antigen.

Indirect ELISA detects patient antibody by using antigen-coated wells and enzyme-labeled anti-human globulin.

Western blot separates proteins by molecular weight and is used as a confirmatory assay for antibodies such as HIV or Lyme disease.

ANA is a screening test for autoantibodies; anti-dsDNA is relatively specific for systemic lupus erythematosus.

Rheumatoid factor is usually IgM directed against the Fc portion of IgG and is sensitive but not specific for rheumatoid arthritis.

Hypersensitivity: type I is IgE-mediated immediate allergy; type II is antibody-mediated cytotoxicity; type III is immune complex disease; type IV is delayed T-cell mediated.

Accuracy is closeness to the true value; precision is closeness of repeated measurements to each other.

Levey-Jennings charts plot quality control results by run and apply Westgard rules, including 1-3s, 2-2s, R-4s, 4-1s, and 10x.

Coefficient of variation = (standard deviation/mean) × 100; it expresses assay imprecision as a percentage.

A reference interval typically covers the central 95% of a healthy reference population, from the 2.5th to 97.5th percentile.

CLIA classifies tests as waived, moderate complexity, or high complexity; each category carries different personnel and quality requirements.

Proficiency testing uses external unknown specimens; unacceptable performance requires investigation and corrective action.

Delta checks compare a current result with the patient's previous result and flag changes exceeding defined limits.

Specimen rejection criteria include unlabeled or mislabeled containers, gross hemolysis, insufficient volume, and improper transport temperature.

Biosafety levels range from BSL-1 for low-risk agents to BSL-4 for dangerous exotic agents requiring maximum containment.