Long-Term Complications in Patients With Hypoparathyroidism Evaluated by Biochemical Findings: A Case-Control Study

Hypoparathyroidism (HypoPT) is associated with an increased risk of various complications, but only few data are available on risk factors. Using a case-control design, we assessed associations between biochemical findings and risk of different complications within a subpopulation of our previously identified Danish patients. We retrieved all biochemical data available on 431 (81% women) patients from the Central Region of Denmark, covering approximately 20% of the Danish population. Average age of patients was 41 years at time of diagnosis. Most patients (88%) had HypoPT due to surgery, mainly due to atoxic goiter and more than 95% were on treatment with calcium supplements and activated vitamin D. On average, time-weighted (tw) plasma levels of ionized calcium (Ca²⁺_tw ) was 1.17 mmol/L (interquartile range [IQR], 1.14 to 1.21 mmol/L) and the calcium-phosphate (CaxP_tw ) product was 2.80 mmol² /L² (IQR, 2.51 to 3.03 mmol² /L² ). High phosphate_tw levels were associated with increased mortality and risk of any infections, including infections in the upper airways. A high CaxP_tw product was associated with an increased mortality and risk of renal disease. Compared to levels around the lower part of the reference interval, lower Ca²⁺_tw levels were associated with an increased risk of cardiovascular diseases. Mortality and risk of infections, cardiovascular diseases, and renal diseases increased with number of episodes of hypercalcemia and with increased disease duration. Treatment with a relatively high dose of active vitamin D was associated with a decreased mortality and risk of renal diseases and infections. In conclusion, risk of complications in HypoPT is closely associated with disturbances in calcium-phosphate homeostasis. © 2018 American Society for Bone and Mineral Research.