Urea and oxalate inhibition of the serum lactate dehydrogenase.

The serum lactate dehydrogenase (LDH) of 16 normal subjects was inhibited by 55 to 68% by the incorporation into the reaction mixture of 0.2 mM-oxalate. Oxalate inhibited the serum LDH of 17 out of 19 patients with myocardial infarction to a greater extent, and that of 16 out of 18 patients with liver disease to a lesser extent than that of the controls. The serum LDH of all 16 patients with liver disease was inhibited by 2 M-urea to a greater degree and that of eight out of nine patients with myocardial infarction to a lesser extent than that of the normal controls (45-62%). The serum LDH of five patients with megaloblastic anaemia was also less sensitive to inhibition by urea than was that of the controls. The inhibitory effect of oxalate was greatest with those sera containing an excess of the electrophoretically fast LDH isoenzymes, while that of urea was most marked with those sera in which the slow LDH isoenzymes preponderated. The results of inhibition studies with urea or oxalate correlated well with other indices of isoenzyme composition. The use of oxalate or urea is recommended as an aid in the enzymatic diagnosis of heart and liver disease, especially when the results of other enzyme tests are equivocal.