Endocrine Abstracts

Introduction: Hypocalcaemia is a complication post-thyroidectomy which requires close monitoring and is treated with oral calcium supplementation. We present a case of iatrogenic hypocalcaemia due incorrect dosing of calcium supplementation because of an institutional protocol, leading to inadvertent patient harm.

Case Report: A 28-year-old female with Graves’ Disease (on methimazole) undergoes a total thyroidectomy. Her post-operative course is complicated by recurrent hypocalcaemia, which resolves with titration of calcium carbonate to 1,500 mg four-times daily, calcitriol 1.5g daily, and 50,000 units of vitamin D weekly. She is subsequently discharged on this regimen, however, represented to the hospital two days later with symptomatic hypocalcaemia (tingling in bilateral upper extremities), and is found to have a calcium of 7.0 mg/dL (1.75mmol/l). She is restarted on her home regimen alongside intravenous calcium gluconate. Despite adherence with her outpatient medication regimen, it was discovered that while she had been receiving 1,500 mg of elemental calcium carbonate during the first admission, she had inadvertently been sent home with 1,500 mg of non-elemental calcium carbonate, which is 40% less than what was required. She was ultimately discharged on the correct regimen, with resolution of hypocalcaemia.

Discussion: Per discussion with the apothecary, our institutional protocol was reviewed, which noted that only the inpatient (and not outpatient) calcium carbonate dosages are listed as the elemental calcium composition. Elemental calcium is 40% of the total calcium carbonate dosage; as a result, our patient was inadvertently sent home on 1,500 mg of calcium carbonate, corresponding to 600 mg of elemental calcium four times per day, which is below the requirement to prevent hypocalcaemia.

Conclusion: It is important to ensure that the calcium supplementation a patient receives is calculated as the elemental calcium. This case depicts iatrogenic hypocalcaemia due to differences in the labelling of prescriptions in the inpatient versus outpatient setting, leading to inadvertent hypocalcaemia and harm.