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Abstract: PO0345

Renal Clearance of Intact and C-Terminal FGF-23 in Man

Session Information

Category: Bone and Mineral Metabolism

  • 402 Bone and Mineral Metabolism: Clinical

Authors

  • Ix, Joachim H., University of California San Diego, La Jolla, California, United States
  • Houben, Alfons Jhm, Maastricht Universitair Medisch Centrum+, Maastricht, Limburg, Netherlands
  • Kroon, Abraham A., Maastricht Universitair Medisch Centrum+, Maastricht, Limburg, Netherlands
  • de Leeuw, Peter W., Maastricht Universitair Medisch Centrum+, Maastricht, Limburg, Netherlands
  • Hoofnagle, Andrew N., University of Washington, Seattle, Washington, United States
  • Ginsberg, Charles, University of California San Diego, La Jolla, California, United States
  • Katz, Ronit, University of Washington, Seattle, Washington, United States
  • Bullen, Alexander, University of California San Diego, La Jolla, California, United States
  • Sharma, Shilpa, University of California Los Angeles, Los Angeles, California, United States
Background

The ratio of C-terminal (cFGF23) to Intact FGF23 (iFGF23) is higher in persons with higher eGFR. Mechanisms are unclear. Differential renal clearance is one possibility.

Methods

Patients were referred for clinically suspected renal artery stenosis (RAS), and maintained off BP meds for 21 days before angiography. This study includes those found without RAS (N=93). Blood was obtained from the aorta (Ao) and bilat. renal veins (RV), and renal blood flow (RBF) was measured using 131Xenon washout. Single pass % reductions of each measure ([Ao – RV/Ao]*100) was calculated, left and right was averaged, and multiplied by RBF to provide renal clearance in ml/min/100g kidney tissue. To determine the relative renal clearance, we calculated the cFGF23/iFGF23 clearance ratio (C/I ratio) and evaluated its relationship with eGFR.

Results

Mean age was 52±11 years, 22% were women, all were white, eGFR was 77±26 ml/min/1.73m2 and directly measured Cr clearance was 72 ± 42 ml/min/100g. Renal clearance of cFGF23 was similar to Cr, while iFGF23 was 37% higher (C/I ratio 0.73 ± 1.10). The clearance of cFGF23 and iFGF23 were directly correlated to eGFR (r=0.31 and 0.35). However, their relative clearance was similar across the range of eGFR (r=0.01). Results were similar in models adjusted for age, sex, and BMI

Conclusion

Renal cFGF23 clearances (which measures both iFGF23 and c-terminal fragments) is similar to Cr, whereas iFGF23 clearance is higher, suggesting that renal clearance of c-terminal fragment clearance is low. While renal cFGF and iFGF23 clearance were both reduced in persons with lower eGFR, the relative efficiency of clearance of cFGF23 vs. iFGF23 appeared similar across the range of eGFR.

Single Pass Percent Reduction and Renal Clearance of C-terminal and Intact FGF23 in Man (N=93)
 Single Pass % ReductionRenal Clearance (ml/min/100g)
Creatinine15.7 ± 8.371.8 ± 41.4
C-terminal FGF2315.5 ± 11.969.7 ± 57.8
Intact FGF2321.6 ± 15.496.9 ± 75.2

Funding

  • NIDDK Support