Kidney Week

Abstract: PO0556

Side Selective Renal Reduction of Intact and C-Terminal FGF-23

Session Information

• Bone and Mineral Metabolism: Clinical
  November 04, 2021 | Location: On-Demand, Virtual Only
  Abstract Time: 10:00 AM - 12:00 PM

Category: Bone and Mineral Metabolism

• 402 Bone and Mineral Metabolism: Clinical

Authors

• Sharma, Shilpa, University of California Los Angeles, Los Angeles, California, United States

Shilpa Sharma, MD, MPH

• Houben, Alfons Jhm, Universiteit Maastricht, Maastricht, Limburg, Netherlands

Alfons Jhm Houben,

• Kroon, Abraham A., Universiteit Maastricht, Maastricht, Limburg, Netherlands

Abraham A. Kroon,

• de Leeuw, Peter W., Universiteit Maastricht, Maastricht, Limburg, Netherlands

Peter W. de Leeuw,

• Hoofnagle, Andrew N., University of Washington, Seattle, Washington, United States

Andrew N. Hoofnagle,

• Katz, Ronit, University of Washington, Seattle, Washington, United States

Ronit Katz,

• Bullen, Alexander, University of California San Diego, La Jolla, California, United States

Alexander Bullen,

• Ginsberg, Charles, University of California San Diego, La Jolla, California, United States

Charles Ginsberg,

• Ix, Joachim H., University of California San Diego, La Jolla, California, United States

Joachim H. Ix,

Background

Relative abundance of FGF23 measured by the C-terminal (cFGF23, which measures both intact FGF23 & c-terminal fragments) vs intact (iFGF23) assays is higher in persons with higher eGFR. Mechanisms are unclear. Individuals with vascular disease often have asymmetric renal function. We compared side selective (R vs L) renal reduction of iFGF23 and cFGF23 within the same individual.

Methods

162 patients were referred for renal angiography at Maastricht University, the Netherlands, for clinically suspected RAS. Participants were maintained off anti-hypertensive meds for 21 days. Blood samples were obtained from the aorta and right (RV) and left renal vein (LV), and renal blood flow was measured using ¹³³ Xenon washout. Creatinine (Cr), cFGF23 (Immutopics), and iFGF23 (Kainos) were measured. Difference of side selective % reductions of each metabolite ([Aorta – (RV or LV)/Aorta]*100) was calculated among each participant. Mean “RV-LV metabolite reduction difference” was calculated across all participants.

Results

Mean age was 54±12 years, 54% were women, and all were white. Mean eGFR was 75±25 ml/min/1.73m² and directly measured Cr clearance during angiography was 72±48 ml/min/100g. Median (IQR) aorta concentrations of cFGF23 was 82 (59, 105) RU/mL, and intact FGF23 was 47(37, 65) pg/mL. The mean difference in R vs. L Cr clearance was 6.0 ± 36.2 ml/min/100g. Side selective reduction differences of both cFGF23 & iFGF23 were significantly related to side selective Cr reduction. Side selective phosphate reduction also associated with iFGF23 reduction independent of Cr reduction, but not cFGF23 (Table). Results were similar in models adjusted for age, sex & BMI.

Conclusion

In hypertensive individuals, the kidney with greater Cr reduction also reduced plasma cFGF23 and iFGF23 more than the contralateral kidney. The kidney that removes more iFGF23 also removes more phosphate, independent of Cr removal; a finding not observed for cFGF23.

Funding

• NIDDK Support