Difference between eGFR cystatin C, eGFR creatinine shows older adults’ kidney function
The difference between eGFR cystatin and eGFR creatinine reveals information about older adults’ kidney functional status that is somewhat explained by muscle quantity and quality, according to data published in Kidney Medicine.
“The difference in eGFR by cystatin C (eGFRCys) vs. creatinine (eGFRCr) has been shown to hold information on functional status, frailty and risk of death in older adults,” O. Alison Potok, MD, from the division of nephrology-hypertension at the University of California in San Diego, and colleagues wrote. “The aim of this study was to determine whether muscle mass explains the association of this difference (eGFRDiff = eGFRCys – eGFRCr) with functional status.”
In a cohort analysis of the Health, Aging and Body Composition (HABC) study, researchers evaluated 2,970 participants (48% were men; 41% were Black; average age was 74 ± 3 years) with cystatin C, creatinine and imaging for muscle mass at baseline.
CKD-EPI equations determined participants' eGFRs, and researchers used the equation (eGFRCys – eGFRCr) to calculate eGFRDiff. Additionally, they measured thigh muscle area in participants with computed tomography.
Using linear regression, researchers modelled the cross-sectional correlation of eGFRDiff and muscle measures. Similarly, researchers used logistic regression to determine the link between eGFRDiff with poor functional status.
The average eGFRCys, eGFRCr and eGFRDiff were 72 mL/min/1.73 m², 68 mL/min/1.73 m² and 4 mL/min/1.73 m², respectively. Participants in the negative eGFRDiff group ( –10 mL/min/1.73 m²) showed a higher risk of comorbidies, slower gait and worse functional status compared with those in the reference group (–10<eGFRDiff10 mL/min/1.73 m²). Additionally, those in the negative eGFRDiff group had about 14 cm² smaller thigh muscle area, but CT scans revealed that lower muscle mass did not reduce the correlation between eGFRDiff and poor functional status.
“This study confirms previous findings that the difference in eGFR between cystatin C and creatinine is clinically relevant and strongly associated with poor functional performance in well-functioning community-living older adults. We demonstrate here that lower eGFRDiff is also strongly associated with lower muscle quantity and muscle strength. Despite eGFRDiff being associated with lower muscle area, low muscle mass did not meaningfully attenuate the relationship of eGFRDiff with functional status,” Potok and colleagues wrote. “Future studies are needed to better understand the determinants of this difference to understand mechanisms responsible for its strong and consistent relationship with frailty, mortality and other clinical outcomes.”
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