ASCP C key terms

Determination of a patient's ABO group by testing red cells with anti-A and anti-B reagents (forward) and serum against A1 and B reagent cells (reverse). A discrepancy between the two methods must be resolved before transfusion.

Test that uses anti-human globulin reagent to detect IgG or complement already bound to a patient's red cells in vivo. A positive result suggests autoimmune hemolysis, hemolytic disease of the newborn, or a delayed transfusion reaction.

Method that detects unexpected antibodies in serum by incubating serum with reagent red cells, washing, and adding anti-human globulin. It is the basis of antibody screens, antibody panels, and the antiglobulin crossmatch.

Testing of patient serum against group O reagent red cells carrying known antigens to detect clinically significant alloantibodies before transfusion or during pregnancy. A positive screen requires identification with a panel.

Compatibility test in which donor red cells are tested against recipient serum, usually through immediate-spin and antiglobulin phases, to confirm that no clinically significant incompatibility exists before transfusion.

Antibody recovered from sensitized red cells by washing the cells and then dissociating bound antibody using acid, heat, or an organic solvent. Eluates help identify the antibody causing a positive direct antiglobulin test.

Anti-D antibody preparation given to Rh-negative mothers to prevent alloimmunization to the D antigen during pregnancy or delivery. It is also considered after inadvertent transfusion of D-positive blood.

Technique in which red cells and reagent are centrifuged through a gel card containing anti-human globulin; agglutinated cells are trapped in the gel, producing stable, graded reaction strengths that are easy to standardize and read.

Calculated difference between measured sodium and the sum of chloride and bicarbonate, reflecting unmeasured anions. It is elevated in ketoacidosis, lactic acidosis, renal failure, and some toxin ingestions.

Sensor that measures the activity of a specific ion such as sodium, potassium, chloride, or calcium through a membrane potential. Direct and indirect (diluted) methods can disagree in samples with very high protein or lipid.

Range containing the central 95% of results from a defined healthy population. Results outside the interval are not automatically abnormal and must be interpreted with the patient's clinical picture and prior results.

Measurement of light absorbance at a chosen wavelength to determine analyte concentration, based on the Beer-Lambert relationship. It underlies most chemistry assays, including enzyme activity measurements.

Glycated hemoglobin fraction that reflects average blood glucose over roughly two to three months. It is used to diagnose and monitor diabetes and is affected by hemoglobin variants, anemia, and altered red cell survival.

Calculation that estimates kidney filtration from serum creatinine plus age and sex, or from a timed urine collection. It is used to stage chronic kidney disease and to adjust drug dosing.

Automated panel reporting red cell, white cell, and platelet counts along with hemoglobin, hematocrit, and red cell indices. Abnormal flags or results prompt a manual smear review.

Percentage or absolute count of newly released immature red cells, reflecting bone marrow response. It rises with hemolysis or blood loss and falls in aplastic or nutritional marrow failure.

Test of the extrinsic and common coagulation pathways; the INR standardizes results across reagent lots for warfarin monitoring. Prolongation occurs with factor deficiency, vitamin K deficiency, and liver disease.

Test of the intrinsic and common coagulation pathways. It is used to monitor unfractionated heparin therapy and to screen for deficiencies of factors VIII, IX, XI, and XII.

Procedure in which patient plasma is combined 1:1 with normal plasma and the clotting time repeated. Correction indicates a factor deficiency, while failure to correct suggests an inhibitor such as a lupus anticoagulant or factor antibody.

Fibrin degradation product released when cross-linked fibrin is broken down. It is sensitive but not specific for thrombosis, so a negative result is most useful for excluding venous thromboembolism in low-risk patients.

Microscopic examination of a stained blood film to verify automated counts, perform a manual differential, and assess red cell, white cell, and platelet morphology such as schistocytes, blasts, or inclusions.

Differential stain that classifies bacteria as gram positive (purple) or gram negative (pink) and describes their shape and arrangement. Results guide preliminary reporting and empiric antimicrobial selection.

Lowest antimicrobial concentration that prevents visible growth of an organism in broth dilution testing. It is interpreted as susceptible, intermediate, or resistant using validated breakpoints.

Isolation of a pathogen on appropriate growth media followed by susceptibility testing, so therapy can be tailored to the organism. Specimen quality and media selection strongly influence the usefulness of results.

Paired aerobic and anaerobic bottles collected with skin antisepsis from each of multiple sites. Adequate blood volume and careful site preparation most influence recovery of organisms and avoidance of contamination.

Identification method that compares a colony's protein mass spectrum against a reference library. It provides rapid, accurate organism identification and is often used directly from positive blood culture bottles.

Immunoassay in which an enzyme-labeled conjugate converts a substrate to a colored product proportional to analyte bound. Formats include sandwich, indirect, and competitive and are used for antigens and antibodies.

Laser-based technique that measures fluorescently labeled cells one at a time, giving counts and phenotypes. It is used for lymphocyte subsets, leukemia and lymphoma immunophenotyping, and CD4 monitoring.

Screening assay, usually by immunofluorescence or immunoassay, for autoantibodies directed against nuclear antigens. Low titers are common in healthy people, so specific follow-up antibody testing is needed for interpretation.

Method that amplifies a target nucleic acid sequence through repeated cycles of denaturation, primer annealing, and extension. It underpins pathogen detection, mutation analysis, and quantitative viral load testing.

Ordered display of a cell's metaphase chromosomes arranged by size, banding pattern, and centromere position. It detects aneuploidy, balanced translocations, and large structural abnormalities requiring dividing cells.

Technique in which fluorescently labeled DNA probes bind specific chromosome regions and are visualized by microscopy. It detects gene fusions, microdeletions, and amplifications in both dividing and interphase cells.

Massively parallel sequencing of many DNA fragments at once, allowing panel, exome, or genome analysis. It detects variants across many genes and can identify low-frequency mutations in mixed samples.

Federal law governing laboratory testing in the United States. It classifies tests as waived, moderate, or high complexity and sets requirements for personnel qualifications, quality control, and proficiency testing.

Control chart that plots quality control values over time against the mean and standard deviation limits. Westgard rules applied to the pattern reveal random error, systematic shifts, and trends.

External program that sends unknown specimens for analysis and compares the laboratory's results with peer or referee values. Acceptable performance is required for CLIA compliance and accreditation.

Comparison of a patient's current result with a previous result to flag possible specimen mislabeling, collection error, or analytic problems. A large unexplained change triggers review before reporting.

Elapsed time from specimen collection or receipt to result reporting. It is monitored as a key performance indicator, especially for stat tests in emergency and inpatient settings.

Standard sequence for filling collection tubes to prevent additive carryover: blood culture bottles, citrate, serum, heparin, EDTA, then oxalate-fluoride tubes. Following it protects test accuracy.

Rupture of red cells that releases hemoglobin and intracellular contents into the specimen. It falsely raises potassium, lactate dehydrogenase, and AST and is a frequent reason for specimen rejection.