Comparison of precision for the Kodak Ektachem 400 and Technicon AutoAnalyzer II creatinine methods

We have evaluated the precision of the Ektachem 400 thin film enzymic creatinine method and compared it to that obtained for an AutoAnalyzer II (AAII) picric acid procedure. The results of the study show that the Ektachem method yields imprecise creatinine values over the low concentration range (40-240 mumol/L). Run-to-run precision estimates at a creatinine concentration of 225 mumol/L (by AAII) yielded CV's of 9.3 and 2.6% for the Ektachem 400 and AutoAnalyzer II methods respectively. The Ektachem 400 yielded imprecise creatinine determinations even when sample ammonia concentrations were less than 150 mumol/L. Patient samples analyzed by the AAII and Ektachem 400 over the creatinine range 40-900 mumol/L were highly correlated (r = 0.994). The correlation (r = 0.779) was low for patient data over the creatinine range 40-160 mumol/L. Creatinine results determined by the Ektachem 400 showed improved precision when samples were evaluated in triplicate using Kodak's latest (No. 8.5) software revision.