MLS key terms

Classification of red cells by A and B carbohydrate antigens, together with the naturally occurring anti-A and anti-B antibodies in plasma; mismatched transfusion can cause acute intravascular hemolysis.

Highly immunogenic protein found on most people's red cells; D-negative individuals can form anti-D after transfusion or pregnancy, so they receive D-negative units and Rh immune globulin.

Procedure that incubates serum with reagent red cells, then adds antihuman globulin to reveal antibodies that bound in vitro; the basis of antibody screening and serologic crossmatching.

Test that adds antihuman globulin to a patient's washed red cells to detect antibody or complement already attached in vivo; positive in autoimmune hemolysis and delayed transfusion reactions.

Compatibility test that mixes donor red cells with recipient serum, either by serologic methods or validated computer systems, to confirm no clinically significant antibody will destroy the units.

The specific substance a procedure measures in a specimen, such as glucose, sodium, or creatinine; the reported concentration refers to this substance rather than to the whole sample.

Range of results expected in a healthy population, usually covering the central 95 percent; clinicians use it to judge whether a patient value is low, normal, or high.

Principle stating that absorbance is proportional to concentration and light path length, letting spectrophotometers convert the light absorbed by a colored solution into a quantitative result.

Calculated difference between measured cations and anions, commonly sodium minus chloride and bicarbonate; a raised gap suggests unmeasured anions such as ketones, lactate, or toxins.

Comparison of a new result with the patient's earlier value, flagging differences beyond a preset limit; this catches specimen mix-ups, labeling errors, and abrupt clinical change.

Clotting time after tissue factor and calcium are added to plasma; it assesses the extrinsic and common pathways and is prolonged by factor VII deficiency, liver disease, or warfarin.

The patient's prothrombin time divided by a normal control value, raised to the power of the reagent's ISI; it standardizes warfarin monitoring across different thromboplastin reagents.

Clotting time after a surface activator and calcium are added to plasma; it screens the intrinsic and common pathways and is used to monitor unfractionated heparin therapy.

Average volume of a red cell, calculated from hematocrit and red cell count; it sorts anemia into microcytic, normocytic, or macrocytic categories and guides further testing.

Percentage or absolute number of newly released red cells that still contain residual RNA; it shows whether the bone marrow is mounting an appropriate response to anemia.

Lowest antimicrobial concentration that visibly prevents growth of a standardized bacterial inoculum; compared with breakpoints, it classifies the isolate as susceptible, intermediate, or resistant.

Differential stain that colors gram-positive organisms purple and gram-negative organisms pink, revealing cell wall structure and giving rapid clues from direct specimens or colonies.

Agar formulated with substances that suppress certain organisms while permitting others to grow, such as MacConkey agar favoring gram-negative bacilli from mixed specimens.

Rapid test detecting enzymes that inactivate penicillin-type drugs; a positive result predicts failure of penicillins and some cephalosporins even when the organism looks susceptible.

Identification method that compares the protein mass spectrum of a colony with a reference library, yielding genus and species in minutes rather than overnight biochemical testing.

Assay in which an enzyme-tagged antibody converts substrate into a colored product, giving sensitive detection or quantitation of antigens or antibodies in serum.

Highest dilution of a specimen that still produces a positive reaction; it quantifies antibody concentration and allows paired samples to be compared over time.

False-negative or falsely low result caused by antibody excess blocking immune complex lattice formation; diluting the specimen brings reactants into the zone of equivalence.

Appearance of detectable antibody, or a meaningful rise in titer, after infection or vaccination; demonstration usually requires paired acute and convalescent specimens.

Method using a dye-labeled antibody to detect a specific antigen directly in a clinical specimen, visualized with a fluorescence microscope for rapid organism identification.

Ratio of urine density to that of water, reflecting dissolved solute concentration; it helps assess hydration and the kidney's ability to concentrate or dilute urine.

Plastic strip bearing chemical pads that change color when dipped in urine, screening for blood, glucose, protein, leukocyte esterase, nitrite, and other substances.

Cylindrical structure molded within a renal tubule from protein and trapped cells; the predominant cast type on microscopy points to particular forms of kidney injury.

Urine albumin divided by urine creatinine on a spot specimen; the ratio corrects for dilution and detects early kidney damage, especially in diabetes.

Centrifuged urine sediment inspected under the microscope for red cells, white cells, casts, crystals, and organisms; completes the routine urinalysis alongside chemical testing.

Technique that copies a target DNA segment through repeated cycles of strand separation, primer annealing, and extension, producing enough product to detect or analyze.

PCR variant that measures fluorescence during each cycle as product accumulates, permitting quantitation and avoiding post-amplification gel analysis.

Cycle number at which fluorescence first crosses a defined threshold during real-time PCR; lower values indicate more target nucleic acid was present initially.

Chain-termination method that reads DNA base by base using labeled dideoxynucleotides; it remains a standard for confirming variants detected by other techniques.

Molecular laboratory practice of moving reagents and specimens in one direction, using separate areas for pre- and post-amplification steps, to prevent amplicon contamination of new reactions.

Testing samples with known values alongside patient specimens to confirm an assay performs within acceptable limits before results are released for clinical use.

External program that sends blinded specimens to a laboratory and compares its results with peer laboratories; participation satisfies accreditation rules and exposes systematic error.

Interval from specimen receipt or order entry until the result is reported; a core service measure that laboratories monitor and reduce through process improvement.

Documented studies demonstrating that an assay meets requirements for accuracy, precision, reportable range, and interference before it is used for patient testing.

Structured investigation that identifies underlying process failures behind an incident and proposes corrective actions, rather than placing blame on an individual worker.