The mainstay of therapy for differentiated thyroid cancer is thyroidectomy [2]. Postsurgical hypocalcemia following thyroidectomy is a common complication because of damage to the parathyroid glands. It also increases health care‐associated expenditure because of increased monitoring requirements, pharmacotherapy, and prolonged hospitalization in addition to patient morbidity, Interventions that minimize postsurgical hypocalcemia are needed in order to improve patient care and waste of resources. In combined results, we found that preoperative calcium and vitamin D supplementation was associated with a reduced incidence of symptomatic hypocalcemia after total thyroidectomy.
The mechanisms of postsurgical hypoPTH are related to disruption of parathyroid arterial supply or venous drainage, mechanical, thermal or electrical injury, and partial or complete removal.[18] Therefore, the most straightforward way to avoid hypoPTH is to limit the extent of thyroidectomy to a unilateral approach.[4] The best prophylaxis to avoid postsurgical hypocalcemia after total thyroidectomy is parathyroid gland preservation during operation to preserve the blood supply to the parathyroid glands.[19] Even when these glands are thought to be well preserved during surgery, normal postsurgical parathyroid function is not guaranteed.[20]
Several interventions to reduce the incidence of postsurgical hypocalcemia have been suggested because patients with symptomatic hypocalcemia undergoes physical and mental suffering.[12] Therefore, routine calcium and vitamin D supplementation is advocated in many clinical centers.[4, 19] These prophylactic approach to prevent postsurgical hypocalcemia is to routine prescription of oral calcium with or without calcitriol.[8, 9] Typically, oral calcium carbonate is the most widely available and inexpensive preparation and is given as 500–625 mg to 1,000–1,250 mg two to three times a day. This routine administration of oral calcium is known to reduce postsurgical hypocalcemia to approximately 10%.[21] Because of low cost and ease of dosing for patients at risk for hypoparathyroidism, we also recommend universal calcium prophylaxis like others.[19]
Vitamin D deficiency is an independent risk factor of postsurgical hypocalcemia.[5] Moreover, the severity of hypocalcemia seems to be remarkably higher in those with lower than normal preoperative vitamin D levels.[22, 23] Therefore, prophylactic treatment of hypocalcemia with vitamin D and calcium is a reasonable strategy with synergy.[24] Impaired PTH secretion results in postsurgical hypocalcemia through by inhibition inhibiting of bone resorption, reduction reducing of 1,25-dihyroxyvitamin D synthesis by the kidneys, and reduced reducing intestinal absorption of calcium.[25] Adding calcitriol (1,25-(OH)2-D3) adds to the cost but increases the effectiveness of oral calcium. It also increases calcium absorption and increasing intestinal calcium transport into the blood. This effect on calcium absorption usually takes few days.[14] Therefore, preoperative supplementation in patients undergoing thyroidectomy with calcitriol are expected to increase the efficacy of routine calcium supplementation in the immediate postsurgical period, thereby decreasing the duration of transient hypocalcemia.[4]
PTH level has also been suggested as a reliable marker of postsurgical permanent hypoPTH.[26] However, development of acute hypocalcemia after thyroid surgery lags behind the decline in the serum PTH level, and the patient may have been from the hospital before their his or her serum calcium having reaches a nadir, which may occur 24–72 hours after thyroidectomy.[4] Therefore, it is important to anticipate the possibility of progressive hypocalcemia, to educate patients about its possible development and steps they should take to avoid and treat it, and to institute preemptive measures that both prevent and correct hypocalcemia in the presurgical period.
Postoperative calcium plus vitamin D is known to be effective in preventing postoperative hypocalcemia and decreasing the demand for intravenous calcium supplementation.[12] This meta-analysis found the role of preoperative oral calcium and vitamin D supplementation in avoiding postsurgical symptomatic hypocalcemia. This prophylactic approach may cause uncommon but serious risks of overshooting and causing hypercalcemia and potential renal injury. Therefore, biochemical monitoring for medication tapering is mandatory.[4] However, the half-life of calcitriol is relatively short (5–8 hours), and toxicity from excessive calcitriol ingestion may be reversed quickly (within days).[4]
Our study has some limitations. First, the studies included for in the meta-analysis was were heterogeneous. There was a high heterogeneity especially between the studies. There is no universal agreement on standardized definitions for postsurgical hypocalcemia and hypoPTH after total thyroidectomy.[11] The reported incidence of postsurgical hypoPTH varies differs greatly, and previous research also suggested that the definition of hypoPTH is not universal throughout the literature.[11] Second, attempting to compare data from the surgical series is difficult and maybe inaccurate. Analysis was even more difficult by the diversity of postsurgical electrolyte supplementation protocols used by different doctors. Third, we cannot define the adequate dosage and duration of calcium and vitamin D intake before surgery, because the regimens of each the study studies were quite variable very different.