Testing the accuracy of total cholesterol assays in an external quality-control program. Effect of adding sucrose to lyophilized control sera compared with use of fresh or frozen sera

Abstract

We studied the suitability of various types of human serum preparations to test the accuracy of total cholesterol measurements in the External Quality Assessment scheme in The Netherlands, in which approximately 180 laboratories participate. Checked against the certified Abell/Kendall Reference Method, large reagent-dependent negative biases were observed with lyophilized serum that was insufficiently cryoprotected. The biases for the reagents of Du Pont, Roche, and Beckman averaged -16.7%, -9.2%, and -7.6% respectively; the least bias, -0.4%, was obtained with reagent from Boehringer Mannheim. The beneficial effect of cryoprotection with sucrose was demonstrated by the decrease in interreagent variation from 5.4% to 1.9%, the latter value being comparable with the values for fresh and once-frozen pooled serum (1.3% and 1.7%, respectively). We conclude that the detrimental effect of lyophilization on serum matrix can be minimized by suitable cryoprotection with 200 g/L sucrose.

A model for harmonization of routine clinical chemistry results between clinical laboratories

“…The calibrator subpools were dispensed into 10-mL vials and were lyophilized according to the procedure described previously. 9 After lyophilization the calibrators were stored at 4 Ê C until further use.…”

“…Normal lyophilized controls are therefore non-commutable and unsuitable as calibrators. 9 Exclusion of the results from the respective reagent sources revealed an improved variation reduction. One solution for this particular problem is the use of control serum samples that are cryoprotected with 20% (g/v) saccharose.…”

“…One solution for this particular problem is the use of control serum samples that are cryoprotected with 20% (g/v) saccharose. 9 The calibrator serum samples used in the present study were not cryoprotected, because saccharose cryoprotection appears to be detrimental for the measurement of a number of other analytes such as sodium. Saccharosesupplemented serum shows 35% higher results when determined by direct ISE techniques compared with indirect ISE methods and ame-photometric analysis (unpublished results from external quality assessment surveys in The Netherlands).…”

Survey of Total Error of Precipitation and Homogeneous HDL-Cholesterol Methods and Simultaneous Evaluation of Lyophilized Saccharose-containing Candidate Reference Materials for HDL-Cholesterol

“…CRMs intended to closely mimic fresh patient sera were developed by the SKZL. Pools were prepared as described previously (17 ). In total, 11 serum pools were made, containing various concentrations of HDL-chol, triglycerides, and cryo-and lyoprotectant (saccharose).…”

“…Finally, CRMs 10 and 11, with medium (4.85 mmol/L triglycerides, mainly VLDL) and high concentrations of triglycerides (15.8 mmol/L triglycerides, mainly chylomicrons), respectively, and a final saccharose concentration of 200 g/L, were prepared from appropriate serum aliquots that were initially frozen with 50 g/L saccharose. Sample preparation and subsequent lyophilization of all CRMs was performed as described previously (17 ). sera used for the validation of the modified cdc reference method procedure A frozen serum pool from the CDC, i.e., AQ15, which is usually used for internal and external quality-control assessment of the HDL-chol Reference Method and the HDL-chol DCM, was used for verifying the HDL-chol accuracy in the 2-mL procedure compared with the 5-mL procedure.…”