Isoenzymes of Lactate Dehydrogenase: Lactate dehydrogenase is a tetrameric enzyme and consists of four subunits. These subunits can occurs in two isoforms i.e. H isoform (for hea), M isoform (for muscle). LDH-1 (4H) - in the hea and RBCs LDH-2 (3H1M) - in the reticuloendothelial system LDH-3 (2H2M) - in the lungs LDH-4 (1H3M) - in the kidneys, placenta, and pancreas LDH-5 (4M) - in the liver and striated muscle Normal value of LDH in serum is 100-200 U/L. LDH level is 100 times more inside the RBC than in plasma, and therefore minor amount of hemolysis will result in a false positive test.