Severe hypocalcemia after parathyroidectomy (PTx) occurs frequently among patients on dialysis with severe hyperparathyroidism, a new study confirms. Importantly, preoperative serum alkaline phosphatase (ALP) levels appear to be the only predictor of early and persistent hypocalcemia, according to investigators.
Juan Carlos Ramirez-Sandoval, MD, MSc, of the Salvador Zubirán National Institute of Health Sciences and Nutrition in Mexico City, Mexico, and collaborators compared 73 patients with secondary hyperparathyroidism (SHPT) and 14 patients with tertiary hyperparathyroidism (THPT) with 146 patients who had primary hyperparathyroidism (PHPT) undergoing PTx. The groups were matched by age, sex, and date of surgery.
Early severe hypocalcemia, defined as free calcium of 3.2 mg/dL or less or corrected calcium of 7.5 mg/dL or less within 48 hours of PTx, occurred in a significantly higher proportion of patients with SHPT/THPT than PHPT: 77% vs 6.8%, respectively, the investigators reported in Nephrology. In the SHPT/THPT group, persistent hypocalcemia, defined as an elemental calcium intake of more than 3.0 g/d to achieve corrected calcium exceeding 8.0 mg/dL, occurred in 77% and 64% of patients at 6 and 12 months following PTx, respectively. In PHPT cases, however, persistent hypocalcemia occurred in just 6.8% after 4 to 12 months following surgery.
Dr Ramirez-Sandoval’s team identified preoperative serum ALP as the only risk factor for early or persistent severe hypocalcemia. Each 1-log increase in preoperative ALP was significantly associated with 7.3-fold and 7.1 odds of early severe hypocalcemia and persistent hypocalcemia, respectively. There were no associations between hypocalcemia and intact parathyroid hormone (iPTH) levels of more than 1000 pg/mL or weight of resected parathyroid tissue.
In other results, patients with persistently low iPTH of less than 50 ng/mL, suggestive of adynamic bone disease, had higher calcium increases and less oral calcium requirements after PTx, as well as less hemoglobin response to erythropoiesis-stimulating agents compared with those who had increasing iPTH. The only risk factor independently associated with persistently low iPTH was a sudden drop of serum calcium within 4 hours of PTx.
“We do not know if an appropriate prophylaxis regimen, consistent with fixed doses of calcitriol or vitamin D analogs prior [to] parathyroidectomy, could prevent the frequency of hypocalcemia,” the investigators stated. “Clinical trials are needed in this regard.”
Fonseca-Correa J, Nava-Santana C, Tamez-Pedroza L, et al. Clinical factors associated with early and persistent hypocalcemia after parathyroidectomy in patients on dialysis with severe hyperparathyroidism. Published online January 27, 2021. Nephrology. doi:10.1111/nep.13854