Association of Serum Calcium and Phosphate With Incident Cardiovascular Disease in Patients With Hypoparathyroidism

The pathophysiological basis for the increased incidence of cardiovascular disease in patients with chronic hypoparathyroidism is poorly understood. To evaluate associations between levels of albumin-corrected serum calcium, serum phosphate, and calcium-phosphate product with the odds of developing cardiovascular events in patients with chronic hypoparathyroidism with ≥1 calcitriol prescription, we conducted a retrospective nested case-control study of patients who developed a cardiovascular event and matched controls without an event. The primary outcome was the instance of cardiovascular events. An electronic medical record database was used to identify 528 patients for the albumin-corrected serum calcium analysis and 200 patients for the serum phosphate and calcium-phosphate product analyses. Patients with ≥67% of albumin-corrected serum calcium measurements outside the study-defined 2.00 to 2.25 mmol/L (8.0 to 9.0 mg/100 ml) range had 1.9-fold higher odds of a cardiovascular event (adjusted odds ratio, 95% confidence interval 1.89, 1.10 to 3.25) compared with patients with <33% of calcium measurements outside the range. Likewise, patients with any serum phosphate measurements above 0.81 to 1.45 mmol/L (2.5 to 4.5 mg/100 ml) had 3.3-fold higher odds (3.26; 1.24 to 8.58), and those with any calcium-phosphate product measurements above 4.40 mmol²/L² (55 mg²/dL²) had 4.8-fold higher odds of a cardiovascular event (95% confidence interval 1.36 to 16.81) compared with patients with no measurements above these ranges. In adult patients with chronic hypoparathyroidism, a cardiovascular event was more likely in those with a higher proportion of albumin-corrected serum calcium measurements outside 2.00 to 2.25 mmol/L (8.0 to 9.0 mg/100 ml) or any serum phosphate and any calcium-phosphate product measurements above the normal population range.