Preparation of an optically clear frozen human control serum

A new method was developed for the preparation of a human control serum. All equipment used will be available in any clinical laboratory. An in-between storage period of 2 months at -20 degrees C for the combined serum pool proved obligatory to obtain a stable, well defined control serum. In our procedure the heavy turbidity inherent to outdated thawed serum is removed by vacuum filtration over Avicel cellulose. The resulting serum filtrate is clarified to a degree such that it can readily be passed through a filterset consisting of four filters with diminishing pore size from 8.0 to 0.22 micron. The time needed for the total filtration of 10 litres will not exceed 2 to 3 h using 90 mm diameter filters. In our experience over a period of more than 3 years, these controls stored at -20 degrees C had a stability of at least 1 year for non-enzymatic as well as most enzymatic components. Information is provided on the stability and concentration levels of components measured by immunological methods, that is, radioimmunoassay and turbidimetry. We monitor 50 parameters with the control serum described.