Plasma creatinine results derived from an endpoint modification of the Jaffé method

For values in the normal pediatric range, endpoint modifications of the Jaffe method for measuring plasma creatinine (PCr) yield higher results than other commonly used techniques. In an effort to evaluate the Olympus AU5000 endpoint method used by the large reference laboratory to which many of our patients are directed by their third-party payor, we compared results with a kinetic Jaffe technique using paired samples from the same specimens. In 46 samples, the kinetic method measured PCr at ≤0.8 mg/dl, whereas the endpoint technique PCr was higher by 0.1 mg/dl in 6 (13%), 0.2 mg/dl in 23 (50%), and 0.3 mg/dl in 16 (35%) samples (P<0.0001). The combination of these higher values and the same reported normal range for all children ages 2–12 years (0.3–1.0 mg/dl) and 13–17 years (0.7–1.4 mg/dl) makes interpretation of Olympus AU5000 endpoint method results difficult, particularly for younger children. The results reinforce the need for each laboratory to provide comprehensive age- and sex-adjusted normal PCr ranges.