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Abstract: TH-PO663

Which Factors Explain the Difference Between Measured and Estimated GFR?

Session Information

  • Geriatric Nephrology
    November 07, 2019 | Location: Exhibit Hall, Walter E. Washington Convention Center
    Abstract Time: 10:00 AM - 12:00 PM

Category: Geriatric Nephrology

  • 1100 Geriatric Nephrology

Authors

  • Sigurdsson, Albert, Landspitali - The National University Hospital of Iceland, Reykjavík, Iceland
  • Palsson, Runolfur, Landspitali - The National University Hospital of Iceland, Reykjavík, Iceland
  • Gudnason, Vilmundur, Icelandic Heart Association, Kopavogur, Iceland
  • Indridason, Olafur S., Landspitali - The National University Hospital of Iceland, Reykjavík, Iceland
Background

Estimated GFR (eGFR) based on serum creatinine (SCr) is frequently reported by clinical laboratories, despite a certain degree of imprecision. The aim of this study was to examine factors that could explain the difference between eGFR and measured GFR (mGFR) in an elderly population.

Methods

We analyzed data from the AGES-Kidney Study, in which 805 individuals above the age of 70 (mean (SD) age 79 (3.9) years) had mGFR values available with simultaneous measurement of SCr and cystatin C. The CKD-EPI equation was used to calculate eGFR based on SCr (eGFRcr) or combination of SCr and serum cystatin C (eGFRcr-cys). The absolute difference between mGFR and eGFR (mGFR – eGFR) was determined and multivariable linear regression used to estimate the association of numerous variables with this difference, including age, sex, medication use, body composition, muscle strength and comorbidities.

Results

Mean (SD) mGFR in the study group was 62.4 (16.4) mL/min/1.73 m2, whereas mean eGFRcr was 65.7 (17.1) mL/min/1.73 m2 and mean eGFRcr-cys 64.7 (17.9) mL/min/1.73 m2. The difference between mGFR and eGFR ranged from –36 to 46 mL/min/1.73 m2 for eGFRcr and –35 to 26 mL/min/1.73 m2 for eGFRcr-cys. In the multivariable linear regression model, significant predictors of the difference between mGFR and eGFRcr were age (p=0.047), thigh muscle mass (measured by computed tomography) (p<0.001), results of timed up and go test (p<0.001), mGFR (p<0.001) and urinary albumin/creatinine ratio (p=0.013). Significant predictors of the mGFR and eGFRcr-cys difference were age (p<0.002), sex (p<0.001), thigh muscle mass (p<0.001) and mGFR (p<0.05).

Conclusion

These preliminary results suggest that several variables, in particular those pertaining to muscle mass and strength, associate with the difference between mGFR and both eGFRcr and eGFRcr-cys. Incorporation of these variables into eGFR equations might yield more precise GFR estimates in the elderly than current equations. In addition, age and sex may not be adequately accounted for in these equations.

Funding

  • Government Support - Non-U.S.