Stability in urea as a measure of cardiac lactate dehydrogenase on the centrifugal analyzer.

Kinetic methods are described for determination of total, heat-stable, and urea-stable lactate dehydrogenase (EC 1.1.1.27) activity on the centrifugal analyzer. In the urea-stable method we present, 2.6 molar urea is used to differentiate lactate dehydrogenase originatingfrom heart and liver.This urea concentration, greater than that used by most other investigators, better differentiates between cardiac and liver lactate dehydrogenase and is as sensitive and specific for cardiac lactate dehydrogenase as the heatstable method; excellentcorrelationwas obtained on 200 specimens assayed by both methods. The ureastable method has the advantages of speed and simplicity, better precision, and decreased serum volume, and is, therefore, preferred to the heat-stable method for determination of cardiac lactate dehydrogenase isoenzymes.