Plasma creatine determination using a luminescence method

Abstract A new luminescence procedure based on the creatine kinase reaction was developed for measuring creatine in plasma. The method is highly applicable to small animal work where the amount of blood volume is critical. Only 20 μl of sample is necessary for creatine analysis. Deproteinizing the plasma sample with ethanol at room temperature is convenient. This extraction method is adaptable to a clinical setting. The ethanol used in the extraction is compatible with the luminescence method but precipitated enzymes in the NADH spectrophotometric method because of the greater sample volume needed for analysis. The creatine concentration is stable in plasma for at least 1 hr in a final anticoagulant concentration of 10 m m EDTA. The correlation between the new luminescence method with the established NADH spectrophotometric method was excellent ( r = 0.99). The accuracy of the within-run precision is high, with a mean coefficient of variation, 2–3%. Plasma creatine levels could be an important indicator denoting early cellular damage and of potential prognostic value. Preliminary studies in human muscle ischemia and early shock in rabbits revealed a significant increase in plasma creatine levels. Further investigations are necessary to evaluate its clinical importance.