[Isoenzymes, methodology and clinical significance (author's transl)]

In recent years the determination of serum enzyme activities has played an increasing role in clinical chemical diagnosis. Because the enzyme composition of single organs is qualitatively and, to a certain extent, quantitatively similar, the diagnostic value of enzyme activity determinations is often diminished. Each serum enzyme can be separated into isoenzymes which stem from different organs and make specific organ diagnoses possible. This separation is possible through chemico-physical and immunological methods. Electrophoretic, chromatographic and immunological methods for the determination of creatine phosphokinase isoenzymes the immunological method is superior to the electrophoretic method in precision and accuracy. Artefacts through storage do not occur in the immunological method. New aspects of the clinical value of the determination of isoenzymes of alkaline phosphatase (AP, E.C. 3.1.3.1), creatine phosphokinase (CK, E.C. 2.7.3.2) and lactate dehydrogenase (LDH, E.C. 1.1.1.27) were studied in the following 8 patient groups: 1. The value of AP isoenzymes for determining liver damage due to chronic alcoholism. 2. The distribution of AP isoenzymes in dialysis patients with special regard to the intestinal isoenzyme. 3. The immunological demonstration of carcino-placental antigen of AP in tumours of the lung. 4. The demonstration of intestinal isoenzymes of AP in chylous effusions. 5. The profile of LDH isoenzymes in pulmonary alveolar proteinosis in serum and in lung lavage-fluid. 6. The usefulness of CK-MB isoenzyme as proff of cardiotoxicity of pharmaceuticals. 7. The profile of CK isoenzymes in central and peripheral nervous system diseases, especially the appearance of CK-BB in serum and the behaviour of CK at the blood spinal fluid barrier. 8. The appearance of unusual isoenzyme patterns in newborn infants and in pregnant women in comparison with normal adults. The determination of isoenzymes is of great clinical importance, even if the total serum activity of the particular enzyme is not elevated.