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Ionised Calcium Drop During Dialysis Acidosis Correction — ESENeph MCQ

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HardElectrolyte DisordersIonised Calcium Drop During Dialysis Acidosis CorrectionESENeph

A 50-year-old man with CKD G4 on haemodialysis develops carpopedal spasm during a dialysis session. His ionised calcium is 0.85 mmol/L (low). His corrected total calcium was 2.15 mmol/L pre-dialysis. What explains the discrepancy?

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Correct answer: B — During dialysis, rapid correction of acidosis (bicarbonate influx from dialysate) increases calcium binding to albumin, reducing ionised (free) calcium even when total calcium appears adequate – this can cause symptomatic hypocalcaemia during dialysis

During haemodialysis, the rapid correction of metabolic acidosis (bicarbonate-containing dialysate normalises blood pH) shifts calcium binding: at higher pH, more calcium binds to albumin, reducing the ionised (physiologically active) fraction. Total calcium may appear adequate but ionised calcium falls, causing symptoms (tingling, carpopedal spasm, Chvostek/Trousseau signs). This is exacerbated by: low dialysate calcium, concurrent Cinacalcet use, and low pre-dialysis calcium. Management includes: increasing dialysate calcium concentration, IV calcium during dialysis, and reviewing calcimimetic timing (Cinacalcet should not be taken immediately before dialysis).

Reference: ERA-EDTA 2019 – Dialysate Prescription; KDIGO 2017 – CKD-MBD