Abstract
Background: The performance of creatinine-based glomerular filtration rate (GFR) estimating equations may vary in subgroups defined by GFR, age and body mass index (BMI). This study compares the performance of the Modification of Diet in Renal Disease (MDRD) study and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations with the revised Lund-Malmö equation (LM Revised), a new equation that can be expected to handle changes in GFR across the life span more accurately.
Methods: The study included 3495 examinations in 2847 adult Swedish patients referred for measurement of GFR (mGFR) 2008–2010 by plasma clearance of iohexol (median 52 mL/min/1.73 m2). Bias, precision [interquartile range (IQR)] and accuracy [percentage of estimates ±10% (P10) and ±30% (P30) of mGFR] were compared.
Results: The overall results of LM Revised/MDRD/CKD-EPI were: median bias 2%/8%/11%, IQR 12/14/14 mL/min/1.73 m2, P10 40%/35%/35% and P30 84%/75%/76%. LM Revised was the most stable equation in terms of bias, precision and accuracy across mGFR, age and BMI intervals irrespective of gender. MDRD and CKD-EPI overestimated mGFR in patients with decreased kidney function, young adults and elderly. All three equations overestimated mGFR and had low accuracy in patients with BMI <20 kg/m2, most pronounced among men.
Conclusions: In settings similar to the investigated cohort LM Revised should be preferred to MDRD and CKD-EPI due to its higher accuracy and more stable performance across GFR, age and BMI intervals.
Acknowledgments
Librarian Elisabeth Sassersson for excellent service regarding literature references.
Conflict of interest statement
Authors’ conflict of interest disclosure: The authors stated that there are no conflicts of interest regarding the publication of this article.
Research funding: Swedish Science Research Council (Project 05196), the Medical Faculty of the Lund University, A. Påhlsson’s, A. Österlund’s, and G. and J. Kock’s Foundations.
Employment or leadership: None declared.
Honorarium: None declared.
Appendix
Calculation of iohexol clearance (=measured GFR)
GFR was calculated from the iohexol concentration with corrections for lack of complete uniform distribution and non-immediate mixing. Initial GFR was calculated as follows:
GFRinitial (mL/min)=[1/(t/V+0.0016)]×ln[Qtot/(V×Ct)]
where t=time interval between injection and sampling (min), ln=natural logarithm, Qtot=injected amount of iohexol (mg), Ct=iohexol concentration (mg/mL) at time (t) after injection and V=distribution volume (mL) calculated as a function of body weight (kilogram) [46]:
Men: 166×weight+2490
Women: 95×weight+6170
To correct for lack of complete uniform distribution of iohexol the correction factor (m) for distribution volume was calculated [26]:
m=0.991–0.00122×GFRinitial
The corrected distribution volume (V*=V/m) was used calculate the final GFR:
GFRfinal (mL/min)=[1/(t/V*+0.0016)]×ln[Qtot/(V*×Ct)]
Body surface area equation of Dubois and Dubois [27].
BSA=0.007184×(weight in kg)0.425×(height in cm)0.725
Equations for estimating GFR
In all equations for estimating GFR given below plasma creatinine (pCr) is expressed in μmol/L (to convert pCr in mg/dL to μmol/L, multiply by 88.4), age in years, height in cm, weight in kg and estimated GFR in mL/min/1.73 m2 body surface area. ln=natural logarithm.
| Revised Lund-Malmö Study equation (LM Revised) [34] | ||
| eX–0.0158×Age+0.438×ln(Age) | ||
| Female | pCr<150 mmol/L: | X=2.50+0.0121×(150–pCr) |
| Female | pCr≥150 mmol/L: | X=2.50–0.926×ln(pCr/150) |
| Male | pCr<180 mmol/L: | X=2.56+0.00968×(180–pCr) |
| Male | pCr≥180 mmol/L: | X=2.56–0.926×ln(pCr/180) |
| CKD-EPI Study equation for Caucasians [4] | ||
| Female | pCr≤62 mmol/L: | 144×(pCr/62)−0.329×0.993Age |
| Female | pCr>62 mmol/L: | 144×(pCr/62)−1.209×0.993Age |
| Male | pCr≤80 mmol/L: | 141×(pCr/80)−0.411×0.993Age |
| Male | pCr>80 mmol/L: | 141×(pCr/80)−1.209×0.993Age |
| MDRD Study equation for caucasians based on IDMS-traceable creatinine assays [3] | ||
| 175×(pCr/88.4)−1.154×Age−0.203×0.742 (if female) | ||
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