Accuracy of creatinine results reported by participants in the CAP Chemistry Survey Program

This report summarizes the creatinine data reported by over 6,000 participants in the 1982 to 1983 College of American Pathologists Chemistry Survey Program. Participants analyzed lyophilized serum samples on a quarterly basis. The most widely used methods employed the kinetic alkaline picrate reaction. Selected samples also were analyzed at the National Bureau of Standards using an isotope dilution-mass spectrometry definitive method. The participant mean results of each method principle group showed positive biases to the definitive values. The kinetic alkaline picrate and enzymatic method groups had the least biases to the definitive values. Excellent correlations between these two method groups and the definitive values were demonstrated. The consensus mean values of these two method groups would provide reliable target values for creatinine in survey samples. Interlaboratory precision improved significantly in each method group as the creatinine concentration increased.