ABPath Chemical Pathology flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

CLIA complexity categories

Waived, moderate, and high complexity. Each category carries distinct requirements for personnel qualifications, quality control, proficiency testing, and inspection frequency under CLIA regulations.

Proficiency testing pass rate

For most regulated analytes, a laboratory must achieve at least 80% correct responses on each proficiency testing challenge to be considered successful; failure triggers corrective action.

Order of draw

Sequence for venous collection: blood culture, citrate, serum separator, heparin, EDTA, fluoride/oxalate. Following this order prevents additive cross-contamination between tubes.

EDTA contamination effect

EDTA from a lavender tube falsely elevates potassium and calcium and lowers magnesium and alkaline phosphatase because EDTA chelates divalent cations and releases intracellular potassium.

Osmolality units

Osmolality is expressed in mOsm/kg of water, whereas osmolarity is mOsm/L of solution. They differ because dissolved solids occupy volume in a liter of solution.

Beer-Lambert law

Absorbance equals molar absorptivity times path length times concentration (A = εbc). It is the basis for spectrophotometric quantitation and is limited by stray light and detector linearity.

Coefficient of variation

CV = (standard deviation / mean) × 100%. It expresses assay imprecision as a percentage, allowing comparison of variability across analytes with different concentration ranges.

Anion gap formula

Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻). Normal is approximately 8–12 mEq/L (or 3–11 if potassium is included); an elevated gap suggests unmeasured anions such as ketones or lactate.

Corrected calcium formula

Corrected calcium (mg/dL) = measured calcium + 0.8 × (4.0 − albumin in g/dL). It adjusts total calcium for albumin binding in hypoalbuminemia.

Westgard 2-2s rule

A rejection rule where two consecutive QC values exceed the mean ±2 SD in the same direction. It detects systematic error and requires rejection of the run.

Westgard R-4s rule

A rejection rule where the difference between two QC values exceeds 4 SD. It detects random error, often when one control is high and another is low.

Levey-Jennings chart

A plot of QC values over time with mean and ±1, 2, and 3 SD limits. It visually reveals shifts, trends, and outliers indicating systematic or random error.

Ion-selective electrode types

Direct ISEs measure undiluted sample activity; indirect ISEs dilute sample first. Direct ISEs better handle hyperproteinemia and hyperlipidemia without pseudohyponatremia.

Relative centrifugal force

RCF = 1.118 × 10⁻⁵ × radius (cm) × rpm². It expresses the gravitational force applied during centrifugation and standardizes separation conditions across centrifuges.

Hook effect

In sandwich immunoassays, extremely high antigen concentrations saturate both capture and detection antibodies, producing falsely low results. Dilution of the sample reveals the true concentration.

Jaffe creatinine method

A picrate-based method that reacts with creatinine but also with proteins and ketones. Compensated Jaffe methods correct for these nonspecific interferences.

HbA1c interpretation

HbA1c reflects average glucose over 2–3 months. Values are affected by hemoglobin variants, anemia, and renal disease, which can falsely alter results.

Phenylketonuria screening

Elevated phenylalanine with normal or low tyrosine on newborn screening suggests PKU. Early dietary restriction prevents intellectual disability.

Winter's formula

Expected PaCO₂ = 1.5 × HCO₃⁻ + 8 ± 2. It predicts respiratory compensation in metabolic acidosis; deviation suggests a mixed acid-base disorder.

Pseudohyponatremia

Falsely low sodium measured by indirect methods in hyperproteinemia or hyperlipidemia. Direct ion-selective electrodes avoid this artifact.

Monoclonal gammopathy

A sharp spike in the gamma region on serum protein electrophoresis suggests a monoclonal protein. Immunofixation identifies the heavy and light chain type.

HbA2 in beta-thalassemia

HbA2 greater than 3.5% on hemoglobin electrophoresis suggests beta-thalassemia trait. Normal HbA2 does not exclude alpha-thalassemia.

INR calculation

INR = (patient PT / normal PT)^ISI. The international sensitivity index standardizes thromboplastin reagents so PT results are comparable across laboratories for warfarin monitoring.

DIC laboratory pattern

Disseminated intravascular coagulation shows prolonged PT and aPTT, low fibrinogen, elevated D-dimer, and thrombocytopenia due to consumption of clotting factors and platelets.

Acute kidney injury criteria

AKI is defined as a rise in serum creatinine of at least 0.3 mg/dL within 48 hours or at least 1.5 times baseline within 7 days, with or without oliguria.

First-trimester screen

Combines PAPP-A, free beta-hCG, and nuchal translucency to estimate risk for trisomy 21 and 18. It is performed between 11 and 14 weeks of gestation.

POC glucose meter limits

Point-of-care glucose meters are affected by hematocrit, altitude, and interfering substances. Results should be confirmed by laboratory testing when clinically discordant.

POC operator competency

CLIA requires documented training and competency assessment for POC operators, along with QC records, to ensure accurate waived testing results.

Hepatitis B serology

HBsAg indicates current infection; anti-HBs indicates immunity; anti-HBc IgM indicates acute infection. These markers distinguish acute, chronic, and resolved infection.

HIV fourth-generation assay

Screens for HIV p24 antigen and HIV-1/2 antibodies. Reactive results require supplemental differentiation or nucleic acid testing to confirm infection.

Acetaminophen nomogram

The Rumack-Matthew nomogram plots acetaminophen level against time since ingestion. It guides N-acetylcysteine therapy for potential hepatotoxicity.

Lithium therapeutic range

Lithium has a narrow therapeutic range of approximately 0.6–1.2 mEq/L. Toxicity causes tremor, ataxia, and renal effects; levels require monitoring.