Patients who’ve had roux-en-Y gastric bypasses have higher incidences of recalcitrant, symptomatic hypocalcemia after thyroidectomies and spend more time in the hospital afterward for intravenous calcium, according to investigators from the Massachusetts General Hospital in Boston.
Because of that, "it is necessary to ensure that all patients with prior RYGBPs [roux-en-Y gastric bypasses] [take] oral calcium supplements before thyroidectomy," and afterward "recalcitrant, postoperative hypocalcemia should be anticipated, calcium levels closely monitored, and early calcium and vitamin D supplementation initiated preemptively," said the researchers, led by endocrine surgery fellow Dr. Travis McKenzie (Surgery 2013;154:1300-6).
Based on the findings, "we recommend starting oral calcium as early as possible in the evaluation phase before thyroidectomy," supplementing with 1.5-2 gm/day of oral calcium, as per American Society for Metabolic and Bariatric Surgery guidelines. "We prefer calcium citrate, because it has better bioavailability when compared with calcium carbonate after RYGBP." Vitamin D–deficient patients should also get calcitriol (0.25 mcg orally twice daily) for 7 days before the operation, they said.
The team compared outcomes in 19 patients who underwent thyroidectomies an average of 53 months after gastric bypass to outcomes in 38 age-, sex-, and body mass index–matched controls, with pre-bypass BMI matched in the study group to pre-thyroidectomy BMI in the control group, about 45 kg/m2 in both cases. Almost all of the patients in both arms had total thyroidectomies, and thyroid malignancies were found in about half of each.
Overall, eight (42%) of the previous-bypass patients, but none of the controls, developed hypocalcemia after thyroid surgery (P less than .01) and four (21%) – but, again, no controls – required intravenous calcium (P less than .01). The need for intravenous calcium, in turn, led to longer hospital stays in the bypass group (2.2 vs. 1.2 days; P = .02). In the bypass group, about 4 patients, 20%, who were on calcium and vitamin D supplements before surgery developed postop symptomatic hypocalcemia, vs. 11 (58%) of those who were not on supplements (P = .18).
Among the 16 bypass patients and 33 controls who did not have intentional parathyroidectomies as part of their operations, both symptomatic postop hypocalcemia (6 patients; 38% vs 0%; P less than.01) and use of intravenous calcium (3 patients;19% vs. 0%; P = .03) were higher in the bypass group.
In addition to preop calcium supplements, all Mass General patients with previous RYGBPs are now started immediately on postop calcium citrate with vitamin D3 (200-mg elemental calcium/tablet), two tablets four times daily, which is continued indefinitely. "We do not feel that higher dosing will increase efficacy as absorption is limited beyond these doses." Patients also get post-op calcitriol (0.25 mcg orally twice daily) for at least a week, and stopped at that point only if there are no symptoms of hypocalcemia, the investigators said.
The problem "is likely multifactorial, including relative hypoparathyroidism after thyroidectomy in the setting of malabsorptive enteric anatomy and metabolic bone disease," they noted.
"An argument has been made that PTH [parathyroid hormone] testing may allow early identification of patients at risk for hypocalcemia after thyroidectomy, prompting early initiation of calcium and calcitriol when PTH is less than [10 mcg/L]. This finding would not change our immediate management since all patients after thyroidectomy in the setting of previous RYGBP are now maintained on both calcium and calcitriol postoperatively. Furthermore, following PTH levels in this unique patient population may not be accurate because secondary hyperparathyroidism is frequently present after RYGBP. In our study group, patients with symptomatic hypocalcemia had an average PTH of [34 mcg/L]," the investigators said.
Patients were, on average, about 50 years old in both study arms, and more than 90% of the subjects were women. No one developed permanent hypoparathyroidism in either arm.
The work was funded in part by the National Cancer Institute and the Massachusetts General Hospital Department of Surgery. Investigator disclosures were not available.