MLT key terms

Testing a person's serum against known A1 and B reagent red cells to detect naturally occurring anti-A and anti-B. Results must agree with the forward cell grouping before an ABO type is reported.

Test that uses anti-human globulin to detect antibody or complement already attached to a patient's red cells in vivo, helping investigate autoimmune hemolysis, hemolytic disease of the newborn, and transfusion reactions.

Test in which serum is incubated with reagent red cells, washed, and exposed to anti-human globulin to reveal antibodies that bind without direct agglutination; the basis of the antibody screen and crossmatch.

Compatibility test between patient serum and donor red cells performed before transfusion; the immediate spin phase detects ABO errors and the antiglobulin phase detects clinically significant antibodies.

A weakened expression of the RhD antigen that may be missed by routine immediate-spin typing and is resolved by antiglobulin-phase testing or molecular genotyping.

Antibody recovered from sensitized red cells by heat, acid, or chemical treatment so it can be tested against panel cells; used when a direct antiglobulin test is positive and the cause is unclear.

Principle stating that absorbance of light is directly proportional to the concentration of the absorbing substance and to the light path length, forming the basis of most spectrophotometric measurements.

Sensor that measures the activity of a specific ion such as sodium, potassium, chloride, or calcium through a selective membrane potential, used in most automated chemistry and blood gas analyzers.

Control chart that plots quality control values over time against lines for the mean and standard deviations, making shifts and trends easy to see from day to day.

Set of statistical decision rules, such as 1-3s, 2-2s, R-4s, and 10x, applied to control results to decide whether an analytical run should be accepted or rejected.

Calculated difference between measured cations and anions, usually sodium minus the sum of chloride and bicarbonate, used to sort metabolic acidosis into high-gap and normal-gap causes.

Release of hemoglobin and intracellular material from broken red cells in a specimen, which can falsely raise or lower analyte results depending on the method and is flagged by a serum index.

Average volume of a red blood cell expressed in femtoliters, calculated from the hematocrit and red cell count, and used to classify anemia as microcytic, normocytic, or macrocytic.

Percentage or absolute number of newly released red cells that still contain RNA, reflecting bone marrow response to anemia or blood loss when corrected for the degree of anemia.

Rate at which red cells settle in a vertical tube in one hour, an indirect and nonspecific marker of inflammation influenced by fibrinogen, immunoglobulins, and red cell shape.

Prothrombin time result standardized with a reference thromboplastin so values can be compared between laboratories and over time, mainly for monitoring warfarin therapy.

Fragment produced when cross-linked fibrin is degraded by plasmin, elevated whenever clotting and fibrinolysis are active; its high sensitivity and low specificity make a negative result useful for excluding thrombosis.

Differential stain that separates bacteria by cell wall structure into gram-positive organisms, which retain crystal violet and appear purple, and gram-negative organisms, which appear pink, while showing shape and arrangement.

Lowest antimicrobial concentration that prevents visible growth of an isolate in a dilution test, used to guide dosing and to interpret whether an organism is susceptible, intermediate, or resistant.

Method that identifies bacteria and yeasts within minutes by matching their protein mass spectra against a reference library, replacing many overnight biochemical identifications in the clinical laboratory.

Agar containing substances such as salts, dyes, or antibiotics that inhibit some organisms while allowing a target group to grow, for example MacConkey agar for gram-negative bacilli.

Paired aerobic and anaerobic bottles inoculated before antimicrobials to detect bacteremia; the volume of blood collected and the timing of collection are the strongest determinants of yield.

Ratio of the density of urine to that of water, reflecting the kidney's concentrating ability; measured by refractometry or a reagent strip pad and interpreted alongside osmolality.

Cylindrical structure formed from Tamm-Horsfall protein within distal tubules, seen in normal concentrated urine after exercise or mild renal hypoperfusion but not specific for renal disease.

Ratio measured on a random urine specimen that estimates twenty-four-hour protein excretion without a timed collection; values above roughly 0.15 grams per gram suggest abnormal proteinuria.

Rules that classify a pleural fluid as an exudate when its protein or lactate dehydrogenase ratio to serum exceeds set thresholds, although they misclassify some transudates.

Technique for examining crystals in synovial fluid; negatively birefringent needle-shaped crystals indicate monosodium urate in gout, while positively birefringent rhomboid crystals indicate calcium pyrophosphate deposition.

Antibody or antigen bound to a solid phase is detected with an enzyme conjugate whose substrate produces a color proportional to the amount of analyte present in the specimen.

Falsely negative or weakly reactive agglutination caused by a large excess of antibody that overwhelms available antigen sites, corrected by diluting the specimen and retesting.

Proportion of people who truly have a condition and are correctly identified by the test; a highly sensitive test is most useful for ruling out disease when the result is negative.

Method in which a fluorochrome-labeled antibody binds its target in cells or tissue and is visualized with a fluorescence microscope, as in antinuclear antibody testing on HEp-2 cells.

External program that sends unknown specimens to a laboratory and compares its results with those of peer laboratories; participation is required for accreditation and reveals systematic errors.

Steps taken to eliminate the cause of a detected nonconformity so the problem does not recur, usually after root cause analysis and followed by checks that the fix worked.

Documented process of proving that an analytical procedure meets defined requirements for accuracy, precision, reportable range, and analytical sensitivity before it is used for patient testing.

Infection control practices applied to all specimens and patients, including hand hygiene, gloves, gowns, eye protection, and safe sharps handling, regardless of known infection status.