Cross comparison of the Limulus test between laboratories. Two European collaborative studies

The results of two independent collaborative interlaboratory surveys evaluating limulus amebocyte lysate assays are presented. We investigated the variation of the results from laboratories all using the same reference endotoxin, but working with different gel-clot techniques. In the first study, four lysates were compared in quantitative gel-clot assays using either a macro- or a microtechnique. In the second study, the performance of a proposed limit test was checked under the auspices of the European Pharmacopoeia Commission. A generally good agreement was reached with the limit test; in the quantitative test, however, considerable interlaboratory variation and significant differences among the lysates were observed. In order to obtain consistent results, a thorough validation of all reagents and test parameters is essential. Collaborative studies are an important tool to detect discrepancies between laboratories and to decrease interlaboratory variability.