skip to main content

Phosphate Removal Session Duration Kinetics — ESENeph MCQ

Instant feedback + full explanation. One question, done properly.

ModerateHaemodialysisPhosphate Removal Session Duration KineticsESENeph

A 70-year-old man with CKD G5D on haemodialysis has serum phosphate 2.4 mmol/L and PTH 95 pmol/L (elevated). He is adherent to sevelamer and dietary advice. His nephrologist recommends intensified dialysis for phosphate control. Which modification is MOST effective for phosphate removal?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — Extending session duration from 4 to 5 hours

Phosphate removal during haemodialysis is primarily limited by slow mobilisation from the intracellular and bone compartments into the extravascular space — not by dialyser clearance. Phosphate exhibits 'rebound' — serum levels rise significantly within 1-2 hours post-dialysis as intracellular phosphate equilibrates. Therefore, extending session duration is the most effective modification, as it allows more time for phosphate to mobilise from tissue stores and be cleared. Increasing blood flow or dialysate flow has minimal additional impact on phosphate removal because the rate-limiting step is tissue-to-blood transfer, not dialyser efficiency. Nocturnal/extended dialysis achieves significantly better phosphate control.

Reference: Daugirdas 2015 – Phosphate Kinetics in Dialysis; KDIGO 2024 – CKD-MBD