Phosphorous Kinetic Modeling in Hemodialysis Patients

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Kapoian T, Khalil S, O’Mara NB, Brink DM, Daugirdas JT: Modeled Daily Ingested, Absorbed and Bound Phosphorus: New Measures of Mineral Balance in Hemodialysis Patients. Am J Nephrol 2019;49:368–376


Control of pre-dialysis (and inter-dialysis) serum phosphorous levels (P) is regarded as a desirable, but challenging, goal in dialytic care of ESKD patients. The level of P in the serum is governed by a complex interplay of a series of processes; namely, dietary P intake and its GI absorption, the distribution of P among the body fluid spaces (including bone), and its removal by the gut, kidney and by dialysis in ESRD patients.

Kapoian and colleagues exploit urea and P kinetic modeling as a novel way to determine and quantify some of these components in hemodialysis (HD) patients, specifically dietary P intake (DPI) and daily absorbed + bound P (DABP), utilizing values for P equivalent binder dosage (EBD).

The modelled DIP was about 12.8mg/kg/d and varied according to body weight (BW) and protein catabolic rate (PCR). The DPI/PCR was about 17.4 for men and 20.1 in women. Not bound and unabsorbed P was about 20% of total DPI, while DABP was about 80% of DPI. Patients took on average about 4.8gms/d of EBD. The kinetic data revealed that a high DPI/PCR, DAPB/PCR, or DIP/BW ratio indicated either a diet rich in soluble, readily absorbed P additives or to non-adherence to prescribed EBD, especially in anuric HD patients (without residual renal function). The nature of food intake (i.e. vegetable/fruit vs animal protein) was not systematically evaluated. This may be important as the P contained in phytates present in vegetables and fruits are poorly absorbed [1] .

The strength of this novel study is that it uses commonly accessible data to construct the modeling programs. Furthermore, it generates parameters that can be useful for detection of non-compliance or excessive consumption of P via foods containing high quantities of added soluble P. It seems mainly applicable to anuric HD patients, and those with substantial residual renal function may require different approaches to kinetic modeling.

Richard Glassock



1. Palmer BF, Clegg DJ: Cardiovascular benefits of a diet enriched with fruits and vegetables. Am J Nephrol 2019; 49:435-437



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Modeled Daily Ingested, Absorbed and Bound Phosphorus: New Measures of Mineral Balance in Hemodialysis Patients