The effect of vitamin D levels on postoperative calcium requirements, symptomatic hypocalcemia, and parathormone levels following parathyroidectomy for primary hyperparathyroidism.

BACKGROUND: Low vitamin D-25 is common in primary hyperparathyroidism but the effect of this deficiency on postparathyroidectomy calcium requirements is unclear.

METHODS: A prospective study was conducted on 4 groups based on preoperative vitamin D-25 levels: very low (<20 ng/mL, n = 500); low (21 to 30 ng/mL, n = 500); normal (>30 ng/mL, n = 500); and supplemented (<25 ng/mL supplemented to >40 ng/mL, n = 285). Patients were placed on identical postoperative oral calcium regimens, and hypocalcemia symptoms were recorded. Total calcium requirements for 2 weeks postoperation were calculated and parathormone (PTH) levels were measured for 2-6 months.

RESULTS: Mean vitamin D levels (ng/mL) for each group were: very low (14.2); low (24.4); normal (38.3); and supplemented (16.5 supplemented to 54.3). Postoperative oral calcium requirements (in grams) were identical for all groups (18.7, 18.2, and 18.6, and 19.0, respectively, all P = NS); the incidence and timing of hypocalcemia symptoms were nearly identical for all groups: 8.1%, 7.9%, and 7.8% (P = .8). Elevated postsurgical PTH was identical (below 8%) and was not influenced by vitamin D levels.

CONCLUSION: The incidence of hypocalcemic symptoms and the postoperative calcium requirements are identical for patients with very low, low, normal, or supplemented (high) vitamin D. The incidence of persistently elevated PTH postoperatively is also unrelated to preoperative vitamin D levels. Vitamin D supplementation from very low to high levels has no clinical benefit.