Determination of serum lactic dehydrogenase by an automatic reaction-rate method

An automatic spectrophotometric reaction-rate method is described for the determination of lactic dehydrogenase (LDH) in blood serum. The method is based on the oxidation of lactic acid in the presence of LDH and diphosphopyridine nucleotide (DPN) to form an absorbing species DPNH. The time required for a small fixed (about 0.06 unit) change in absorbance is measured automatically and related to the LDH concentration. Automatic results obtained on samples containing 0.05 to 0.2 ml of serum show good proportionality and a coefficient of variation of 1.3%. Serum samples (0.2 ml) are analyzed at a rate of 15 to 20 per hour.