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Kidney Week

Abstract: PO2332

Muscle Is a Non-GFR Determinant of Serum Filtration Marker Levels and Is Associated with Differential Accuracy of GFR Estimating Equations in Older Adults

Session Information

Category: CKD (Non-Dialysis)

  • 2101 CKD (Non-Dialysis): Epidemiology, Risk Factors, and Prevention

Authors

  • Flanagin, Erin, Tufts Medical Center, Boston, Massachusetts, United States
  • Tighiouart, Hocine, Tufts Medical Center Institute for Clinical Research and Health Policy Studies, Tufts Medical Center Institute for Clinical Research and Health Policy Studies, Boston, MA, US, academic/medres, Boston, Massachusetts, United States
  • Delgado, Cynthia, San Francisco VA Health Care System, San Francisco, California, United States
  • Gudnason, Vilmundur, Icelandic Heart Association, Haskoli Islands, Reykjavik, Iceland
  • Levey, Andrew S., Tufts Medical Center, Boston, Massachusetts, United States
  • Inker, Lesley Ann, Tufts Medical Center, Boston, Massachusetts, United States
Background

Current GFR estimating equations using creatinine are limited by association with muscle. It is not known whether this is true for recently developed equations using novel filtration markers. These associations are relevant for older adults in whom reduced muscle mass is common.

Methods

In a cross-sectional analysis of 540 community dwelling older adults in Reykjavik, Iceland, serum levels of creatinine (Cr), cystatin-C (Cys), and novel filtration markers (beta-trace protein [BTP], beta-2-microglobulin [B2M], N-acetylthreonine, pseudouridine, phenylacetylglutamine, and tryptophan) were measured, and GFR was measured using clearance of iohexol (mGFR). GFR was estimated from Cr, Cys, or panels of novel filtration markers using CKD-EPI equations. Thigh muscle area (TMA) was assessed using computed tomography.

The association of each filtration marker with TMA was determined using linear regression with adjustment for mGFR, GFR measurement error, age, and sex. The performance of the estimating equations was assessed using bias and percent of large (≥30%) errors (1-P30) among those in the lowest sex-specific quintile of TMA compared to the upper four quintiles.

Results

Mean age was 80 (SD 3.8) years, with a mean mGFR of 63 (SD 16) ml/min/1.73m2. After adjusting for mGFR, all filtration markers had a residual association with TMA, but Cr had a substantially greater association even after adjustment for age and sex. Both bias and 1-P30 were greater in the subgroup with low TMA for eGFR from Cr and/or Cys but not for panel eGFR equations (see figure).

Conclusion

Panel eGFR may be preferable in older adults with low muscle mass. Practical tests are needed to identify individuals with low muscle mass for whom eGFR from Cr and Cys may be less accurate.

Funding

  • Other NIH Support