Therapeutic Plasma Exchange and Changes in Calcium, Phosphate, Parathyroid Hormone, and Fibroblast Growth Factor-23

Abstract

Context: Therapeutic plasma exchange (TPE) removes plasma proteins and other unwanted substances, causing nonspecific alterations of plasma components. A previous study showed an approximately 70% reduction in vitamin D metabolites following a single TPE treatment, prompting further investigation into TPE's effects on vitamin D regulators and metabolites: calcium, phosphate, parathyroid hormone (PTH), and fibroblast growth factor-23 (FGF-23).

Objective: This study examined changes in plasma and effluent levels of total calcium, phosphate, PTH, and FGF-23 in individuals undergoing TPE.

Methods: Measurements were taken immediately before, immediately after, and at follow-up. Paired t tests compared the percentage changes in metabolites from pre- to post-TPE.

Results: Study participants (N = 42) had a mean age of 55 ± 16 years, 28 (67%) were female, and 32 (76%) were White. TPE led to acute changes in calcium (-9%; 95% CI, -11% to -8%), phosphate (-14%; -18% to -11%), and FGF-23 (-12%; -18% to -6%) concentrations. In contrast, PTH levels increased (91%; 63%-119%) from baseline to post-TPE. While most metabolites returned to baseline by the follow-up visit (median 4 [interquartile range, 3-7] days), nearly 25% of patients experienced persistent asymptomatic hypocalcemia. This persistent calcium deficit was not fully corrected by continuous intravenous calcium gluconate infusions administered during the study, nor by the endogenously increased PTH levels.

Conclusion: These findings underscore the need for improved care protocols and vigilant monitoring of mineral metabolism in TPE patients, especially those receiving long-term treatment. Further research is warranted to understand the enduring effects of TPE on mineral metabolism and develop strategies to prevent complications.

Keywords: FGF-23; PTH; calcium; phosphate; therapeutic plasma exchange (TPE).

Figure 1.

Percentage changes in total corrected calcium, phosphate, PTH, FGF-23, 25D, and 1,25D from pre– to post–therapeutic plasma exchange (TPE) (N = 42). Acute reductions in all metabolites, except for an increase in PTH.

Figure 2.

A to F, Comparison of metabolite levels (mean ± SD) from pre– to post–therapeutic plasma exchange (TPE) for A, calcium; B, phosphate; C, PTH; D, FGF-23; E, 25D; and F, 1,25D, respectively (N = 42). The gray shaded areas indicate reference ranges for each metabolite: calcium (8.5-10.3 mg/dL), phosphate (2.5-4.5 mg/dL), PTH (10-65 pg/mL), FGF-23 (19.9-52.9 pg/mL), 25D (20-60 ng/mL), 1,25D (18-78 pg/mL). All observed changes were statistically significant (P < .001).

Figure 3.

Magnesium levels before and after a single therapeutic plasma exchange (TPE) procedure. Pre-TPE (n = 14); post-TPE (n = 13). Gray shaded area indicates reference range 1.7 to 2.2 mg/dL. No statistically significant difference was observed (P = .39).