Persistent hypocalcemia associated with therapeutic plasma exchange performed to reduce HLA antibody levels in cardiac transplant recipients.

Background: Patients who receive heart transplants may undergo therapeutic plasma exchange to reduce high levels of HLA antibodies which may increase the risk of allograft rejection. Plasma exchange may predispose to hypocalcemia because of chelation of calcium by sodium citrate, used as an anticoagulant both during the procedure and in thawed fresh frozen plasma often used for replacement.

Methods: We report three adults with dilated cardiomyopathy who underwent cardiac transplantation and serial plasma exchange for high levels of HLA antibodies. We followed these patients' pre-exchange serum calcium levels and the quantity of calcium supplementation they received. Further, we examined myocardial tissue sections post-transplantation for calcium deposition.

Results: Our patients' serum calcium levels were initially normal, but, despite aggressive calcium repletion, remained low (nadirs for pre-exchange ionized calcium in two patients 4.48 and 3.8mg/dL, respectively, reference range 4.6-5.4mg/dL). For patient 3, pre-exchange total calcium on day 2 was 7.9mg/dL (reference range 8.4-10.2mg/dL). Two patients had intermittent symptoms of hypocalcemia. Studies of cardiac tissue sections (available only from these two patients) were consistent with the presence of calcium deposition post transplantation. In comparison, six patients who underwent lung transplantation and plasma exchange for high levels of HLA antibodies did not manifest significant hypocalcemia.

Conclusions: We emphasize the need for prompt and sufficient calcium replacement, monitored by serum ionized calcium levels, in the early post-cardiac transplantation period when plasma exchange is performed with thawed fresh frozen plasma replacement. The persistently low serum calcium levels we observed post heart transplantation were possibly contributed to by increased myocardial calcium influx.