Enliven: Bio analytical Techniques

Glomerular filtration rate and staging of chronic kidney disease (CKD) is typically assessed by measuring the endogenous concentrations of creatinine. Bioanalytical use of creatinine is also increasing for drug development leading to greater FDA scrutiny. Creatinine is commonly measured by the rapid and inexpensive colorimetric Jaffe reaction. However, the Jaffe reaction is notoriously inaccurate and very small shifts in creatinine cause large miscalculations in CKD staging. While attempts have been made to improve Jaffe reaction assays, an enzymatic assay for creatinine is more accurate and more stable. We review substances found in many common disease states that create chromo gens that interfere is the Jaffe reaction but do not affect the enzymatic assay. This includes cephalosporin antibiotics, glucose, and bilirubin. We also provide a framework for modifying creatinine commercial kits for drug development studies. Most creatinine kits, whether using Jaffe or enzymatic chemistry, are based on the Clinical and Laboratory Standard Institute (CLSI) validation approach, which is designed to distinguish diseased from healthy, is not suitable for use in drug development. The benefits of enzymatic creatinine assays have been demonstrated for over a decade yet the Jaffe reaction continues to be the primary method of measurement demonstrating the need for continued education and nuanced recommendations. For clinical lab use, we highlight a two-phase reflexive method that balances cost and accuracy. For critical decisions during a drug development study, the data strongly supports the use of the enzymatic creatinine assay in combination with bioanalytical method validation for the high accuracy needed in these settings.