While biochemical markers of diseases of the heart have undergone substantial evolution since the first report in 1954 of the utility of aspartate aminotransferase in patients with myocardial infarction, the utility of creatinine as an indicator of renal impairment has remained essentially unchanged for well over 100 years. Also largely unchanged is the method used by many laboratories to measure creatinine. The colorimetric Jaffe method, despite its nonspecificity for creatinine, is still used by more than half of the laboratories in the US for measuring creatinine. Rapid analysis time and low cost are often cited as the primary reason for maintaining the colorimetric method. An enzymatic creatinine assay been available for some time now. However, despite its greater specificity and lack of interference from many common interferences that affect the colorimetric method, the enzymatic method has not gained universal acceptance.
Discrepancies between creatinine and other indicators of renal impairment such as cystatin C can occur as a result of physiological influences, as this case likely demonstrates, or it can occur due to interferences in the creatinine assay, particularly if the colorimetric Jaffe method is used for measuring creatinine. Notable interferences in the colorimetric Jaffe method include ketones, bilirubin, and plasma free hemoglobin due to hemolysis. Measurement of creatinine in newborns and infants using the colorimetric Jaffe method can be particularly problematic as the above mentioned interfering substances are often present. It is not clear in this case whether any of these substances were present that could have contributed to a false increase in the measured creatinine, nor is the method used to measure creatinine stated. However, the time course showing the linear decrease in measured creatinine following surgery to repair the hernia and reimplant the ureter likely demonstrates the recirculation of creatinine as the discrepancy between the 2 markers.
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Authors' Disclosures or Potential Conflicts of Interest: No authors declared any potential conflicts of interest.
- Received for publication November 23, 2016.
- Accepted for publication December 1, 2016.
- © 2016 American Association for Clinical Chemistry