Venous serum, capillary serum, and capillary plasma compared for use in determination of lactate dehydrogenase and aspartate aminotransferase activities.

Lactate dehydrogenase and aspartate aminotransferase activities in capillary serum or plasma were significantly greater than in simultaneously assayed venous serum, the greatest differences being between capillary and venous serum. Although some difference is attributable to tissue fluid contributions, platelets seem to account for most of it, with possible small contributions from leukocytes. Capillary tube size and type appear to be important factors. We recommend that when capillary blood is to be used for enzyme assay, it should be processed as plasma.