Background: Traditional internal quality control schemes for qualitative infectious serology mostly rely on the use of commercial positive and negative quality control materials. However, with respect to the negative control, target values provided by the manufacturer are often poorly defined and non-commutability of the commercial materials further complicates correct interpretation of control results. An alternative quality control procedure using the median patient seronegative response is presented.
Study design: Daily patient median responses were calculated for our Hepatitis B surface antigen, Hepatitis B core antibody, Hepatitis C antibody and HIV antigen/antibody test systems. Because of the low prevalence of these viruses in our area, most patient responses are negative. A minimum of 5 patient samples per day was required to generate a stable daily median. Control limits were calculated and daily patient medians were plotted against commercial quality control results.
Results: Commercial negative controls and daily patient medians mostly behaved in the same way. Nevertheless, for the Hepatitis B surface antigen test, patient medians frequently exceeded the calculated control limit in contrast to commercial quality controls. This confirms that target ranges provided by the manufacturer are not always adequate. Moreover, an important matrix-related interference occurred on our HIV antigen/antibody test system and correct interpretation was only possible using daily patient median results.
Conclusion: Monitoring the daily patient median response can be a valuable alternative to traditional commercial negative quality control. It's easy to perform, cost-free, provides additional information with respect to matrix effects and allows for the establishment of well-defined control limits.
Keywords: Hepatitis B Virus; Hepatitis C Virus; Human Immunodeficiency Virus; Infectious Serology; Quality Assurance; Quality Control.
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