Proficiency testing in immunopathology: establishing the homogeneity of test material
Abstract
Aims: To develop a technique for homogeneity testing of serum aliquot samples suitable for use in the Quality Assurance Program in Clinical Immunology (QAP Pty Ltd). Methods: Albumin was selected as the surrogate protein marker for the product to be tested and the coefficient of dispersion (COD) calculated as the measure of homogeneity. To detect changes in the average level of homogeneity, cumulative sum control (cusum) charts were used. Results: The COD(%) for each triplicate reading of albumin obtained from 34 specimens was normally distributed with a mean of 0.49% and a standard deviation of 0.25%. In industrial quality control schemes the action line is generally set at the upper 99% confidence limits, hence any triplicate sample would be considered to have acceptable homogeneity if the COD was ≤1.08%. Cusum charts were created to monitor albumin homogeneity over time. Conclusions: The use of albumin measurement as the surrogate appears statistically suitable for homogeneity testing in QAP programs for immunodiagnostic testing. CUSUM charts are particularly useful to monitor such homogeneity testing.