Individual-Level Differences ID'd Between Measured, Estimated GFR

Population-level differences between mGFR and eGFRCR small, but individual-level differences large
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TUESDAY, July 5, 2022 (HealthDay News) -- There is considerable individual-level discrepancy between measured glomerular filtration rate (mGFR) and estimated glomerular filtration rate (eGFR), according to a study published online July 5 in the Annals of Internal Medicine.

Tariq Shafi, M.B.B.S., from the University of Mississippi in Jackson, and colleagues quantified the magnitude and consequences of the individual-level differences between mGFRs and eGFRs in four epidemiologic cohort studies involving 3,223 participants. Urinary iothalamate and plasma iohexol clearance were used to measure GFR, while eGFR was calculated based on serum creatinine concentration alone (eGFRCR) and with cystatin C.

The researchers observed small population-level differences between mGFR and eGFRCR, with a median difference of −0.6, but individual-level differences were large. At an eGFRCR of 60, 50, 80, and 95 percent of mGFRs ranged from 52 to 67, 45 to 76, and 36 to 87, respectively. At an eGFRCR of 30, 50, 80, and 95 percent of mGFRs ranged from 27 to 38, 23 to 44, and 17 to 54, respectively. There was considerable disagreement seen in staging of chronic kidney disease by mGFR and eGFRCR. Among patients with an eGFRCR of 45 to 59, 36 and 20 percent had an mGFR of >60 and <45, respectively, while among those with an eGFRCR of 15 to 29, 30 and 5 percent had an mGFR >30 and <15, respectively. There was no substantial improvement noted with eGFR based on cystatin C.

"Clinicians need to recognize that the eGFR is not an mGFR replacement and consider eGFR's inaccuracy while managing individual patients," the authors write.

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