Stability of the CK-MB isoenzyme on routine storage

Unlike earlier studies on the stability of the CK-MB isoenzyme carried out on control sera and on semi-purified and purified CK isoenzymes, we have studied the stability of CK-MB measured electrophoretically in patient sera under different laboratory storage conditions. The values obtained if the test was done immediately were significantly higher than those done on stored samples. There was no difference between specimens stored at -20 degrees C overnight or kept at room temperature (RT) for a few hours, but values were significantly lower (p less than 0.005) in specimens left at RT for 6 h and then stored overnight at 4 degrees C. To determine the effects of longer storage, further specimens stored either at -20 degrees C or at 4 degrees C for up to 4 days were also tested for CK-MB stability by electrophoresis and by immunoinhibition and immunoenzymetric methods. The immunological methods were included in the study to assess method dependency of CK-MB stability. CK-MB was stable at -20 degrees C by all methods, but at 4 degrees C, CK-MB was stable only by immunological and not by electrophoretic (p less than 0.005) measurement. Specimens stored under adverse conditions (4-6 days at RT) showed 50% deterioration of CK-MB when measured electrophoretically but only about 20% when measured immunologically.