How does the MDRD Study equation compare with serum creatinine in routine healthcare? Anatomy of MDRD‐eGFR

Abstract

The Modification of Diet in Renal Disease Study equation-estimated glomerular filtration rate (MDRD-eGFR) as a marker for chronic kidney disease, with a single decision level for both genders and all adult ages, requires that the calculated quantity is independent of gender and age. In a retrospective study of S-Creatinine concentrations from laboratory information systems of hospitals in the UK and Sweden, comprising about 140,000 results in total, it was found that the MDRD-eGFR indeed differs between genders and that it varies with age more than the S-Creatinine concentration does. If the age compensation is deleted from the algorithm, the relative changes in the MDRD-eGFR decrease and become almost the same as those for S-Creatinine concentrations. The difference between the genders could probably be overcome by increasing the "if female factor". We used Pt-Iohexol and S-Creatinine concentrations measured simultaneously to estimate the performance of the MDRD-eGFR in relation to Pt-Iohexol clearance. The Pt-Iohexol varies considerably between patients with the same S-Creatinine concentrations, a difference that is not reflected in the MDRD-eGFR. It is concluded that the mathematical transformation of S-Creatinine concentrations does not add any diagnostic value. On the contrary, an increased measurement uncertainty is unavoidable with the use of factors and exponents. The uncertainty is greater than any difference between age and gender in adjacent age groups. There is no compensation for the individual relation between S-Creatinine and Iohexol clearance, and the equation does not consider the individual body surface area; it is therefore inadvisable to use the MDRD-eGFR values as the basis for administration of drugs excreted by the kidneys.

Gender Differences in Chronic Kidney Disease: Underpinnings and Therapeutic Implications

“…Although the variable sex is included in some but not all such estimations, they do not differentiate an athletic woman or a small, lean man. In a retrospective study, the Modification of Diet in Renal Disease Study equation-estimated glomerular filtration rate (MDRD-eGFR) was suggested to differ between sexes and to vary with age more than the serum creatinine concentration does [30] . Thus, it is possible that incorrect GFR estimation may over/underestimate renal function, perhaps influencing results from large epidemiological studies (inferring misclassification of CKD stage) and/or clinical decisions such as medication prescription.…”

Focusing on the clinical impact of standardization of creatinine measurements: a report by the EFCC Working Group on Creatinine Standardization

“…Narva encourages the use of the MDRD equation for drug dosing adjustment in adults (10). However, some authors have argued that the use of factors and exponents for the mathematical transformation of serum creatinine results increases uncertainty, and therefore the MDRDderived GFR values cannot be recommended as the basis for administration of drugs excreted by the kidneys (20). In contrast, implementation of the CKD-EPI formula (6) in place of the MDRD formula will not have much clinical impact on this specific application since drug dose adjustment is rarely needed in patients with GFR)60 mL/min.…”

Function and longevity of renal grafts from high‐KDPI donors

“…32 Nevertheless, formulas such as the MDRD or CKD-EPI equations 19,33 are universally used in clinical practice as they are valid alternatives to the more expensive and often not attainable direct measure of eGFR. 19,34,35 In addition, although the reliability of the CKD-EPI equation declines for very low or a very high values of eGFR, [36][37][38][39][40] it is unlikely that the results of this study were critically affected by the limitations of the formula, since the same instrument was used for all measurements.…”