‘Substantial discrepancies’ exist between eGFR and measured GFR
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Discrepancies between eGFR and measured GFR suggest that measured GFR may be the superior calculator for diagnosing kidney disease, according to a speaker at ASN Kidney Week.
“A very important clinical question to ask is, ‘For a person with an eGFR, what is the potential range of that person’s [measured GFR (mGFR)]?’” Xiaoqian Zhu, PhD, MS, of the University of Mississippi Medical Center in Jackson, Mississippi, said. “The goal of our study was to evaluate the reliability of eGFR at the individual patient level in multiple ways.”
Researchers evaluated eGFR from serum creatinine alone (eGFRCR) and cystatin and creatinine (eGFRCYS-CR) using the Chronic Kidney Disease Epidemiology Collaboration equations without race coefficients from four U.S. community-based cohorts. All cohorts included mGFR as part of a research protocol.
Quantile regression was used to measure the individual-level reliability of the eGFR by calculating a 95% prediction interval. Zhu and colleagues also analyzed population-level reliability of the eGFR with standard metrics, such as median difference (eGFR-mGFR).
Among the 3,223 participants, the median age was 61 years. In the study, 32% of participants were Black and 55% were women. Overall, the median mGFR was 68 mL/min/1.73 m2. At a population level, the median difference between eGFRCR and mGFR was small (1.4 mL/min/1.73 m2), but at the individual level, the 95% prediction interval of the eGFRCR was large, ranging from 53 mL/min/1.73 m2 to 120 mL/min/1.73 m2 at eGFRCR 90 mL/min/1.73 m2 and from 19 mL/min/1.73 m2 to 55 mL/min/1.73 m2 at eGFRCR 30 mL/min/1.73 m2.
Additionally, 15% of participants with eGFRCR of less than 60 mL/min/1.73 m2 and 28% of those with eGFRCR of less than 30 mL/min/1.73 m2 had mGFR above those thresholds.
According to a press release from ASN, the discrepancy in eGFR and mGFR within racial groups was larger than between-group differences. “For example,” the ASN wrote, “at a calculated eGFR of 60 mL/min/1.73 m2, the mGFR ranged from 32 [mL/min/1.73 m2] to 91 mL/min/1.73 m2 for Blacks and 37 [mL/min/1.73 m2] to 86 mL/min/1.73 m2 for whites, substantially larger and overlapping ranges than the 5 mL/min/1.73 m2 group difference between Blacks and whites.”
“Clinical implications of our study include eGFR is useful but not always a replacement for mGFR,” Zhu said. “Research implications include investigating new GFR measurement techniques which are less cumbersome and have lower variability is essential, and cost-effectiveness studies are needed to examine during which instances mGFR are needed.”
Limitations of the study include single measurements of mGFR and serum markers, as well as combined data from cohorts that used different methods of GFR measurement, according to the researchers.
“Our results suggest that the eGFR calculation should be reported with the associated range of uncertainty,” study co-author Tariq Shafi, MD, MHS, of the University of Mississippi Medical Center, said in the press release. “Our results also indicate that in some instances, clinical decisions may need to be based on measured rather than estimated GFR.”
References:
Study compares different assessments of kidney function. https://www.newswise.com/articles/study-compares-different-assessments-of-kidney-function?sc=mwhr&xy=10007438. Published Nov. 3, 2021. Accessed Nov. 11, 2021.
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Zhu X, et al. Quantifying individual-level uncertainty in GFR estimation. Presented at: ASN Kidney Week; Nov. 4-7, 2021 (virtual meeting).
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