The measurements of secretory granule proteins such as HNL, ECP and others in serum require strict standardization of the sampling procedure as to time and temperature in order to avoid large variations in results. In previous studies SST-tubes were often used with success. However, since some years such tubes have been modified in order to shorten coagulation time, mostly by adding larger amounts of silica microcrystals to the tubes. Such crystals seriously interfere with the release of the granule proteins. In tubes from some vendors this interference may result in reduction in release and in tubes from other vendors the result is accellerated release.
Avoid blood collection tubes containing clot activators in the form of silica microcrystalls!!!