The determination of lactic dehydrogenase with a tetrazolium salt

A colorimetric method for the measurement of lactic dehydrogenase activity has been described, utilizing phenazine methosulfate as an intermediate agent for electron transfer from DPNH to a tetrazolium salt (INT). The use of gelatin to keep the formazan in colloidal suspension provided the added advantage of improving electron transfer via a phenazine methosulfate gelatin complex over that obtained with soluble diaphorase or phenazine methosulfate alone. Several compounds were studied for their ability to act as intermediate electron-transfer reagents, but none were superior to phenazine methosulfate. The sensitivity of the new method is comparable to others measuring either DPNH or pyruvate; its advantages are those of brevity and simplicity. Normal human sera were found to contain from 50 to 100 units of lactic dehydrogenase. The importance of avoiding hemolysis of the blood has been re-emphasized, and the possibility has been demonstrated that a 10-15% overestimation may occur due to hemolysis even when gross hemolysis cannot be recognized.