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Nonlinearity of high-density lipoprotein cholesterol determinations is matrix dependent
1Clinical Pathology Department, Clinical Center, National Institutes of Health, Bethesda, MD 20892.
Clinical Chemistry
|March 1, 1994
Summary
Most high-density lipoprotein (HDL) cholesterol tests failed linearity surveys due to the sample matrix. Nonlinearity originates in the precipitation step, impacting accurate HDL cholesterol measurement.
Area of Science:
- Clinical Chemistry
- Biochemical Assays
Background:
- Accurate measurement of high-density lipoprotein (HDL) cholesterol is crucial for cardiovascular risk assessment.
- Previous linearity surveys revealed widespread method failures in HDL cholesterol determination.
Purpose of the Study:
- To investigate the cause of nonlinearity in HDL cholesterol measurement methods.
- To determine if the survey material matrix is responsible for observed method failures.
Main Methods:
- Evaluated linearity of multiple HDL cholesterol assays (Ektachem, TDx, Sigma, Dimension, Cobas Fara, Hitachi 736).
- Utilized dextran sulfate or phosphotungstate as precipitating reagents.
- Tested linearity using College of American Pathologists (CAP) survey material, control materials, and a fresh serum pool.
Main Results:
- All tested methods exhibited nonlinearity with CAP survey material.
- Five of eight methods showed linearity with control materials precipitated before dilution.
- All methods, except one, were linear with a fresh serum pool, indicating matrix-dependent nonlinearity.
Conclusions:
- The precipitation step is a significant source of nonlinearity in HDL cholesterol assays.
- The sample matrix, not the assay chemistry itself, is the primary determinant of linearity failures.