CLEN CHIM

Quality Assurance (QA)

Includes maneuvers in the pre-analytic, analytic, and post-analytic phases of laboratory testing.

Pre-analytical phase

Involves test ordering, specimen collection, transport, processing, entering patient information, centrifuging, separating aliquots, and delivery to the laboratory.

Analytical phase

Involves specimen analysis, use of commercial controls, and record keeping.

Post-analytical phase

Involves reporting results, physician contact, monitoring quality performance, and total quality control.

Quality Control (QC)

Concerned with the analytic phase of QA, monitoring the reliability of laboratory results in terms of accuracy and precision.

External QC

Monitors accuracy of laboratory tests, established by Belk, using Youden plots.

Internal QC

Monitors day-to-day performance of laboratory tests, established by Levey, using Levey-Jennings chart.

Analytical errors

Systematic errors caused by factors in the analytical system, such as calibration issues.

Personnel errors

Random errors affecting several analyses, such as mislabeling or incorrect data entry.

Trend

Systematic drift or error where values move continuously away from the mean in one direction.

Shift

Abrupt change from the established mean continuing in a linear fashion.

Increased dispersion

Suggests random error with high or low outliers due to variations in instrument operation or clerical errors.

Westgard Multi-Rule Technic

A set of rules for interpreting control data to identify errors in laboratory testing.

Accuracy

Extent to which the mean measurement is close to the true value, expressed as absolute or relative error.

Precision

Reproducibility of a laboratory determination under identical conditions, expressed in terms of standard deviation or coefficient of variation.

Reliability

Ability of a test to maintain accuracy and precision over time.

Sensitivity

Ability of a test to detect the smallest amount of analyte, characterized by a low probability of false negatives.

Specificity

Ability of a test to detect analyte without detecting other analytes, characterized by a low probability of false positives.

Control

A solution with known constituents used to verify the accuracy of test results.

Standard

A solution of known characteristics and value used as a reference for calculations.

Figures of Merit

Major factors in analytical methods include accuracy, precision, limit of detection, sensitivity, and specificity.

Direct measurement

Involves measuring two components directly to obtain a result.

Indirect measurement

Involves measuring one or more components to derive another value.

Substitution

A method to determine an unknown value based on known values.

Chemical measurement

Includes absolute methods (gravimetric, volumetric) and relative methods (instrumental).

Colorimetry

Involves Beer’s law, stating that analyte concentration is proportional to light absorption.

Spectrophotometry

Measures light absorption and transmittance in solutions.

Absorbance (OD)

Describes the amount of monochromatic light absorbed by a sample.

Monochromator

Device that isolates specific wavelengths of light for analysis.

Cuvet holder

Holds the cuvet containing the analyte solution for measurement.

Detector

Converts light signals into electrical signals for detection.

Turbidimetry

Measures light blocked by particles in a turbid solution.

Nephelometry

Measures light scattered by particles in suspension.

Reflectance spectrophotometry

Measures reflected light to determine concentration.

Fluorescence

Emission of light by a molecule after absorbing light of a shorter wavelength.

Bioluminescence

Chemiluminescence where excitation energy comes from a chemical reaction.

Atomic absorption spectrophotometry (AAS)

Measures light absorbed by nonionized atoms at specific wavelengths.