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Abstract: TH-PO207

Intestinal Phosphorus Absorption Assessment by Kinetic Modeling of 33P Radiotracer in Hemodialysis Patients

Session Information

Category: Bone and Mineral Metabolism

  • 402 Bone and Mineral Metabolism: Clinical

Authors

  • Hill Gallant, Kathleen M., Purdue University, West Lafayette, Indiana, United States
  • Stremke, Elizabeth, Purdue University, West Lafayette, Indiana, United States
  • Trevino, Laurie, Indiana University, Indianapolis, Indiana, United States
  • Moe, Sharon M., Indiana University School of Medicine, Indianapolis, Indiana, United States
  • Wastney, Meryl E., Metabolic Modeling Services, Blenheim, New Zealand
Background

Intestinal phosphorus (P) absorption is an important component of P homeostasis. In CKD, limiting P absorption is the goal of many pharmacologic therapies. 24-hr urine P has been used as a surrogate for P absorption, but recent balance studies demonstrate that this measure is highly variable and not related to net P absorption (Stremke, CJASN 2018). Further, 24-hr urine P is not useful in oliguric/anuric patients. Changes in serum P are equally problematic due to diurnal variation, fluxes with dialysis, and erratic dietary intake. We tested a 33P absorption method as a sensitive and direct assessment of P absorption in humans that can be used for clinical research in hemodialysis (HD) patients.

Methods

HD patients with stage 5D CKD were enrolled. Following 10 days of controlled study diet (~800 mg/d P), patients underwent HD and then were admitted as inpatients to a clinical research center for 2 days for P absorption testing. 33P radiotracer was administered PO with a meal containing a load of ~300 mg P, and blood sampled over 24-hr. The next day, a second dose of 33P was administered by IV and blood sampled for another 24-hr, followed by a second HD treatment. Serum 33P activity was measured by liquid scintillation, adjusted for decay and expressed as % of dose. The 33P data were analyzed by compartmental modeling using WinSAAM software. Intestinal absorption was calculated as the fraction moving into blood vs. moving down the intestinal tract into stool. Descriptive results from 14 unique subjects are presented.

Results

Serum P increased during the 48-hr of study that was during an interdialytic interval. To estimate how much additional P (i.e., over absorption) was entering the system, a second model was used. Average fractional P absorption was 58±17%. The absorption test was well-tolerated by patients in the study. Complications were limited to difficulties with venous access in some patients.

Conclusion

Fractional P absorption can be estimated directly by a test using oral and IV 33P administration; the test is feasible and well-tolerated in HD patients. This novel methodology can be used for clinical studies aimed at assessing physiology, pathophysiology, or interventions related to P absorption in HD patients.

Funding

  • NIDDK Support