Capillary tubes for microhematocrit are used for the centrifugation of blood samples. Heparinized capillaries should be used when the samples are not immediately sealed with wax and centrifuged. The heparinized coating delays the clotting of the blood. The heparinization is applied as a thin, homogeneous coating on the tube. This enhances the immediate dissolving of the heparin in the blood and prevents agglutination.