Counting platelets in platelet concentrates on hematology analyzers: a multicenter comparative study

Hematology analyzers are designed to count whole blood samples, but are also used by blood centers to perform quality control on blood components. In platelet (PLT) concentrates, the number of PLTs is approximately fivefold higher and red blood cells are absent, causing variable PLT counting results. It was our aim to compare currently used hematology analyzers for counting PLTs in PLT concentrates using fixed human PLTs.

PLT samples were fixed, diluted into seven concentration levels (plus one blank), aliquoted, and shipped to 68 centers. Evaluable data were obtained for 89 hematology analyzers. All samples were counted six times, and results were reported to the coordinating center. The overall group mean was calculated, and the percentage deviation from this mean was calculated for each analyzer.

At PLT levels relevant for blood centers, 750 x 10(9) to 2000 x 10(9) per L, analyzers gave results that were between 35 percent lower and 16 percent higher than the overall group mean. Within a group of analyzers, results were comparable with coefficient of variations usually below 10 percent, indicating that the observed differences were caused by instrument characteristics. A smaller study with fresh, unfixed PLT samples showed that analyzers behaved similarly for fixed and fresh PLTs.

With a wide array of currently used hematology analyzers, a marked difference was determined for the PLT counts of fixed human-based identical samples provided to 68 laboratories by a centralized facility. A gold standard method is needed to allow for more valid interlaboratory comparisons between hematology analyzers.