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Abstract: PO2515

Determinants of Serum Phosphate Concentration in CKD

Session Information

Category: CKD (Non-Dialysis)

  • 2103 CKD (Non-Dialysis): Mechanisms

Authors

  • Dharia, Sunny, Albany Medical College, Albany, New York, United States
  • Phelps, Kenneth R., Albany Stratton VA Medical Center Albany, Albany, New York, United States
  • Der Mesropian, Paul J., Albany Stratton VA Medical Center Albany, Albany, New York, United States
  • Shaikh, Gulvahid G., Albany Stratton VA Medical Center Albany, Albany, New York, United States
  • Kovesdy, Csaba P., The University of Tennessee Health Science Center College of Medicine, Memphis, Tennessee, United States
  • Gosmanova, Elvira O., Albany Stratton VA Medical Center Albany, Albany, New York, United States
Background

The serum phosphorus concentration (SP) is the sum of rates of P excretion and reabsorption per volume of filtrate (EP/Ccr and TRP/Ccr). EP/Ccr is calculated as UPxScr/Ucr (U-urine, S-serum, P-phosphorus, cr-creatinine). In a steady state, EP/Ccr rises as P intake rises or Ccr falls. TRP/Ccr, calculated as SP – EP/Ccr, is hormonally regulated. We aimed to analyze the evolution of SP and its determinants over CKD stages G1-G5 (dialysis excluded).

Methods

This was a retrospective study involving 200 US veterans followed in the nephrology clinic of the Albany VAMC from 1/2020 to 4/2021. CKD stages were based on 4-variable MDRD eGFR. There were 293 simultaneous random measurements of SP, UP, Scr, Ucr, PTH, and eGFR. Means of these parameters were plotted against CKD stage. Correlations among variables were determined with linear regression models.

Results

The mean age (SD) of the cohort was 73 (10) years. 96% were male, and 48% had diabetes. In comparison to stages G1-2, EP/Ccr rose and TRP/Ccr fell significantly starting at stage G3b (Figure). EP/Ccr correlated with eGFR (R2 = 0.28, p < 0.001), but TRP/Ccr and SP did not. SP correlated with EP/Ccr (R2=0.24, p<0.001) and TRP/Ccr (R2=0.38, p<0.001). PTH correlated with EP/Ccr (R2= 0.32, p<0.001), and TRP/Ccr correlated with [PTH] (R2= 0.10, p< 0.001).

Conclusion

EP/Ccr rises consistently as eGFR falls. At stage G3b, the decrement in TRP/Ccr equals the increment in EP/Ccr, and SP remains stable. In stages G4 and G5, the rise in EP/Ccr is greater than the fall in TRP/Ccr, and SP ascends accordingly. As eGFR declines, PTH rises, but its apparent effect on TRP/Ccr is blunted. As CKD progresses, maintenance of stable SP depends primarily on reduction of intestinal P absorption.

Funding

  • Veterans Affairs Support