Background:
Hypocalcaemia is a rare side-effect of plasmapheresis. It occurs secondary to the use of citrate as an anticoagulant, to maintain patency of plasmapheresis circuits. While the hypocalcaemia associated with this procedure is not typically critical, it can lead to tetany and arrhythmias (1). This is especially the case with pre-existing hypocalcaemia, which can lead to citrate toxicity.
Clinical case:
A 37 year old lady with bilateral sequential single lung transplants performed in 2008 for cystic fibrosis underwent plasmapheresis on four separate occasions over the last four years, including twice in 2020. The treatment was required for antibody mediated rejection. On each of these occasions, despite oral calcium and vitamin D supplementation, she developed hypocalcaemia as low as 1.80mmol/L. She was symptomatic with perioral tingling and paraesthesia the first time this occurred, and required intravenous calcium gluconate therapy.
Fortunately, no arrhythmias or tetany were identified with the hypocalcaemia. However, she did develop hypotension with her most recent course. Her calcium levels recovered post-plasmapheresis and were maintained at a mid-reference range level with her usual supplementation otherwise. Whilst undergoing plasmapheresis, she required oral calcium 4800mg/day. Pathology during her most recent course identified CKD with an eGFR varying between 40-50mL/min/1.73m2, PTH 7.9pmol/L, 25(OH) vitamin D 104nmol/L, phosphate 1.04mmol/L, magnesium 0.73mmol/L, TSH 0.82mIU/L, fT4 11.7pmol/L, albumin 35g/L and normal lipid studies and liver function tests.
This case demonstrates the importance of monitoring calcium levels closely in patients undergoing plasmapheresis, as patients can develop symptomatic hypocalcaemia. There may even be a role for pre-emptive treatment to reduce the risk of hypocalcaemia in patients with a known history of having such a response to plasmapheresis. Particular attention should be given to patients with a history of hypoparathyroidism (including surgical and medication induced, such as with PPIs) or pre-existing hypocalcaemia.