ASCP MLT cheat sheet

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

RhD-negative recipients should receive RhD-negative red cells when possible; RhIG prevents anti-D alloimmunization in Rh-negative mothers exposed to Rh-positive fetal cells, ideally within 72 hours.

A positive antibody screen requires antibody identification; clinically significant antibodies react at 37°C or AHG and can cause hemolytic transfusion reactions or hemolytic disease of the fetus/newborn.

DAT detects antibody or complement coating red cells in vivo; IAT detects unexpected antibodies in patient serum during screening and crossmatching.

RBC storage: 1–6°C for up to 42 days in additive solution; platelets: 20–24°C with agitation up to 5 days; FFP: ≤ −18°C for up to 12 months.

Febrile nonhemolytic reaction is the most common transfusion reaction; acute hemolytic reaction from ABO incompatibility causes fever, flank pain, hypotension, hemoglobinuria, and DIC.

Tube crossmatch phases: immediate spin detects ABO incompatibility; 37°C incubation and AHG phase detect IgG and complement-binding clinically significant antibodies.

Lewis antibodies are usually IgM, do not cross the placenta, and often react at room temperature; they are generally not clinically significant for transfusion.

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

Anion gap = Na − (Cl + HCO3); reference ~8–12 mmol/L; elevated gap suggests unmeasured anions such as ketones, lactate, urea, or toxins.

Calculated osmolality = 2Na + glucose/18 + BUN/2.8 (mg/dL); measured osmolality exceeds calculated in osmolar gap from methanol, ethylene glycol, or isopropanol.

Corrected calcium = measured Ca + 0.8 × (4.0 − albumin); hypoalbuminemia lowers total calcium without lowering ionized calcium.

Friedewald LDL = total cholesterol − HDL − triglycerides/5; invalid when triglycerides >400 mg/dL.

Henderson-Hasselbalch: pH = 6.1 + log(HCO3− / (0.03 × pCO2)); respiratory acidosis has increased pCO2, metabolic acidosis has decreased HCO3−.

BUN/creatinine ratio >20:1 suggests prerenal azotemia, dehydration, or upper GI bleeding; ratio <10:1 suggests liver disease or low protein intake.

HbA1c reflects average glycemia over about 2–3 months; it is not reliable in hemolytic anemia, recent transfusion, or hemoglobin variants.

Troponin I or T is the preferred biomarker for acute myocardial injury; CK-MB is less specific and may rise after skeletal muscle injury.

MCV = (Hct × 10)/RBC (millions/µL); MCH = Hgb × 10/RBC; MCHC = Hgb × 100/Hct.

Microcytic anemia (MCV <80 fL): iron deficiency, thalassemia, anemia of chronic disease, sideroblastic anemia; macrocytic (MCV >100 fL): B12/folate deficiency, alcohol, liver disease, hypothyroidism.

Corrected reticulocyte count = reticulocyte % × (patient Hct / normal Hct); reticulocytosis indicates increased marrow response, reticulocytopenia suggests marrow failure or untreated deficiency.

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

DIC: thrombocytopenia, prolonged PT and aPTT, low fibrinogen, elevated D-dimer/FDPs, and schistocytes on smear.

PT/INR monitors warfarin (extrinsic pathway); aPTT monitors unfractionated heparin (intrinsic pathway); both are prolonged in DIC and severe liver disease.

Normal platelet count ~150–450 ×10^9/L; spontaneous bleeding is uncommon until <20 ×10^9/L.

Hct ≈ RBC (millions/µL) × MCV (fL)/10; a discrepancy between spun Hct and calculated Hct may indicate cold agglutinins or lipemia.

ESR is elevated by anemia, pregnancy, infection, inflammation, and malignancy; it is low in polycythemia, sickle cell disease, and hypofibrinogenemia.

Gram-positive cells stain purple due to thick peptidoglycan; gram-negative cells stain pink and have an outer membrane containing lipopolysaccharide.

MacConkey agar selects gram-negative bacilli; lactose fermenters (E. coli, Klebsiella) form pink colonies; non-lactose fermenters (Pseudomonas, Salmonella) are colorless.

Staphylococcus aureus is catalase positive and coagulase positive; coagulase-negative staphylococci are catalase positive and coagulase negative.

Pseudomonas aeruginosa is oxidase positive; Enterobacteriaceae are oxidase negative; oxidase testing helps differentiate nonfermenters from enteric bacilli.

Urease-positive organisms include Helicobacter pylori and Proteus species; urease splits urea to ammonia and raises pH.

Blood cultures should be collected before antimicrobial therapy, from at least two sites, with aerobic and anaerobic bottles; volume of blood is a key determinant of yield.

Bacterial meningitis CSF: neutrophilic pleocytosis, low glucose, high protein, and often positive Gram stain; viral meningitis usually has lymphocytic pleocytosis and normal glucose.

MIC is the lowest antimicrobial concentration that inhibits visible growth; susceptibility breakpoints classify organisms as susceptible, intermediate, or resistant.

Acid-fast bacilli retain carbol fuchsin after acid-alcohol decolorization; Kinyoun and Ziehl-Neelsen stains are used for mycobacteria.

IgG crosses the placenta and mediates secondary responses; IgM is the first antibody in a primary response and fixes complement efficiently; IgA is secretory; IgE mediates allergy.

Primary immune response: slow, mainly IgM; secondary response: rapid, higher titer, mainly IgG with increased affinity.

Complement classical pathway is activated by IgG/IgM-antigen complexes; alternative pathway by microbial surfaces; lectin pathway by mannose-binding lectin.

Type I: IgE/mast cells; Type II: IgG/IgM against cell-bound antigens; Type III: immune complex deposition; Type IV: T-cell-mediated delayed hypersensitivity.

ELISA uses enzyme-labeled antigen or antibody and a substrate to produce a measurable color signal proportional to target concentration.

HIV screening uses a fourth-generation antigen/antibody immunoassay; reactive results require differentiation or confirmatory testing such as HIV-1/2 antibody differentiation or nucleic acid testing.

Hepatitis B surface antigen (HBsAg) indicates current infection; anti-HBs indicates immunity; anti-HBc IgM suggests acute infection; HBeAg indicates high infectivity.

ANA is a screening test for autoimmune connective tissue disease; anti-dsDNA and anti-Sm are more specific for systemic lupus erythematosus.

Urine dipstick: pH, specific gravity, protein, glucose, ketones, blood, leukocyte esterase, nitrite, bilirubin, and urobilinogen are common chemically detected parameters.

Specific gravity by refractometer estimates urine concentration; 1.010 is isosthenuric, >1.020 concentrated, and <1.005 dilute.

Microscopic hematuria: >3 RBC/hpf; dysmorphic RBCs and RBC casts suggest glomerular bleeding.

WBC casts indicate pyelonephritis or interstitial inflammation; RBC casts indicate glomerulonephritis; hyaline casts are nonspecific and can be normal.

Calcium oxalate crystals are envelope-shaped and may follow ethylene glycol ingestion; triple phosphate crystals are coffin-lid shaped and occur in alkaline urine.

Urine hCG is a qualitative pregnancy test; very early pregnancy or dilute urine can produce false-negative results.

Renal threshold for glucose is about 180 mg/dL; glucosuria occurs when blood glucose exceeds this threshold or when proximal tubular reabsorption is impaired.

Bence Jones protein is a monoclonal light chain; it may be missed by routine dipstick protein and requires serum/urine protein electrophoresis or immunofixation.

Light's criteria for pleural fluid: exudate if pleural protein/serum protein >0.5, pleural LDH/serum LDH >0.6, or pleural LDH >2/3 upper normal serum LDH.

Levey-Jennings chart plots QC results over time with mean and ±1, ±2, ±3 SD limits; trends suggest systematic error and shifts suggest calibration or reagent problems.

Westgard 1-3s: one control beyond ±3 SD; 2-2s: two consecutive beyond same ±2 SD; R-4s: range between two controls >4 SD; 4-1s: four consecutive beyond same ±1 SD; 10x: ten consecutive on one side of mean.

Order of draw: blood culture, coagulation citrate, serum separator, heparin, EDTA, glycolytic inhibitor; fill citrate tube to the indicated volume to avoid dilution.

EDTA prevents clotting by chelating calcium and is used for CBC; heparin inhibits thrombin and is used for chemistry and osmotic fragility; citrate is used for coagulation tests.

Critical values must be reported promptly to a responsible clinician and documented with time, recipient, and read-back.

Delta checks compare current results with prior values and flag significant changes that may indicate specimen mix-up, analytical error, or clinical change.

Proficiency testing evaluates laboratory performance against peer laboratories; unacceptable results require investigation and corrective action.

Standard precautions require gloves for all blood/body fluid contact; PPE includes gown, mask, and eye protection when splash exposure is possible.

Specimen rejection criteria include unlabeled or mislabeled containers, inadequate volume, hemolysis, clotted anticoagulated samples, and improper transport temperature.