ABPath Clinical Pathology key terms

A statistic that expresses how far a laboratory's result for a proficiency testing challenge lies from the peer group mean, measured in units of the peer group standard deviation. Values beyond plus or minus two often trigger investigation.

A quality control graph that plots control results over time against established mean and standard deviation limits. It lets staff visually detect shifts, trends, and out-of-control events in an analytical run.

A set of statistical decision rules, such as 1-3s and 2-2s, applied to control measurements to decide whether an analytical run should be accepted or rejected. They balance error detection against false rejection.

An external program in which unknown samples are sent to a laboratory and results are compared with peer laboratories or a reference value. It provides objective evidence of testing competence for regulatory compliance.

A rule that compares a patient's current result with a previous result for the same analyte and flags differences exceeding a defined threshold. It helps detect specimen mix-ups, mislabeling, and acute clinical changes.

A test result so far outside normal limits that it may indicate imminent danger to the patient and requires prompt notification of the responsible clinician. Documentation of the notification is required.

The interval between the time a specimen is received or an order is placed and the time the result is reported. It is a core operational metric for laboratory service quality.

The span of analyte concentrations over which a method produces results meeting defined accuracy and precision criteria without dilution or concentration. Also called the linear range.

The lowest analyte concentration that can be reliably distinguished from zero, typically with a stated probability of false positive and false negative error. It differs from the limit of quantitation.

The central range of values, usually covering 95 percent of a healthy reference population, against which patient results are interpreted. It is method and population dependent.

The difference between measured cations and anions, usually sodium minus the sum of chloride and bicarbonate. An elevated gap suggests accumulation of unmeasured anions such as lactate, ketones, or toxins.

The difference between measured osmolality and calculated osmolality from sodium, glucose, and urea. An increased gap suggests the presence of unmeasured osmoles such as alcohols or glycols.

A calculation comparing the change in anion gap with the change in bicarbonate to detect mixed acid-base disorders. It helps determine whether an additional metabolic process is present.

An adjustment of total calcium for the prevailing albumin concentration, since roughly half of serum calcium is protein bound. It estimates the physiologically active calcium fraction when ionized calcium is unavailable.

The free, unbound fraction of calcium in blood that is physiologically active. It is affected by pH and is the preferred measure in critically ill patients or those with abnormal albumin.

A spectrophotometric estimate of free hemoglobin in a specimen, reported as a graded value. It alerts clinicians and laboratorians to possible interference with chemistry and hematology results.

Optical and volume effects caused by high lipid content in a specimen that can falsely alter photometric and other measurements. Detection often uses a turbidity index or ultracentrifugation.

A semiquantitative measure of bilirubin pigment in a specimen that flags possible interference with photometric assays. High values can bias results for analytes measured at overlapping wavelengths.

The average volume of circulating red cells, calculated from hematocrit and red cell count. It is the primary classifier of anemia as microcytic, normocytic, or macrocytic.

A measure of the variation in red cell size, usually reported as a coefficient of variation. An elevated value indicates anisocytosis and helps distinguish mixed or early nutritional anemias.

The percentage or absolute number of immature red cells containing residual RNA. It reflects bone marrow erythropoietic response and separates hypoproliferative from regenerative anemias.

A fragmented red blood cell seen on peripheral smear, often with helmet or triangular shapes. Increased numbers suggest microangiopathic hemolysis, mechanical valve damage, or disseminated intravascular coagulation.

A dense, round red cell lacking central pallor due to membrane loss. It is characteristic of hereditary spherocytosis and immune-mediated hemolysis.

A test that detects antibody or complement bound to a patient's red cells using antihuman globulin reagent. It is central to diagnosing immune-mediated hemolysis and hemolytic disease of the newborn.

A test that detects unexpected antibodies in a patient's serum by incubating serum with reagent red cells, then adding antihuman globulin. It is used for antibody screening and crossmatching.

A procedure that tests a patient's serum against group O reagent red cells to detect clinically significant unexpected antibodies before transfusion or pregnancy. A positive screen requires identification.

A mismatch between forward and reverse ABO typing or unexpected reactions in either direction. Causes include weak subgroups, missing antibodies, rouleaux, and clerical errors and must be resolved before transfusion.

The lowest concentration of an antimicrobial agent that visibly inhibits growth of a standardized bacterial inoculum. It quantifies susceptibility and guides dosing and breakpoint interpretation.

A susceptibility method in which antibiotic-impregnated disks are placed on an inoculated agar plate and zone diameters are measured. Zones are interpreted against standardized tables to categorize isolates.

A defined antimicrobial concentration or zone diameter used to categorize an organism as susceptible, intermediate, or resistant. Breakpoints are set by consensus bodies and updated as resistance evolves.

A mass spectrometry technique that identifies microorganisms by comparing their protein spectral fingerprints with a reference library. It provides rapid, accurate species-level identification from colonies.

A screening assay, commonly immunofluorescence on HEp-2 cells, that detects antibodies directed against nuclear antigens. Pattern and titer guide further testing for connective tissue diseases.

A method using an enzyme-labeled reagent that converts a substrate to produce a measurable signal proportional to analyte or antibody concentration. Variants include sandwich, competitive, and capture formats.

An assay in which antibody binding to antigen consumes complement, and residual complement is detected by its ability to lyse sensitized indicator red cells. It is used for certain serologic and autoimmune tests.

A technique using fluorescently labeled DNA probes to detect specific chromosomal sequences in interphase or metaphase cells. It is used for translocations, amplifications, and microdeletions.

A full description of an individual's chromosome complement, including number and structural abnormalities, obtained by banding and microscopic analysis of metaphase cells. It detects balanced rearrangements and aneuploidy.

An in vitro method that amplifies a targeted DNA sequence through repeated cycles of denaturation, primer annealing, and extension. It enables sensitive detection of pathogens and mutations.

A genetic change whose association with disease is not yet established by available evidence. It should not be used alone for clinical management decisions and may be reclassified as data accumulate.

A high-throughput technology that sequences many DNA fragments in parallel, enabling panels, exomes, and genomes to be analyzed. Interpretation requires careful variant filtering and confirmation.