Associations of serum 25-hydroxyvitamin D with circulating PTH, phosphate and calcium in patients with primary...

Despite NIH clinical recommendations, many clinicians are reluctant to replace vitamin D in patients with hypercalcaemia with primary hyperparathyroidism (PHP) due to concerns over aggravating hypercalcaemia. Furthermore, the optimum level of vitamin D replacement in PHP remains unclear.

We performed a large retrospective study to determine whether a relationship exists between serum 25-hydroxyvitamin D levels, calcium and other important biochemical markers in patients with PHP. Serum, plasma and urinary biochemical measurements were collected from 251 patients with hypercalcaemia diagnosed with PHP.

When examining overall mean circulating levels during clinical follow-up, serum 25-hydroxyvitamin D correlated highly significantly with plasma parathyroid hormone (PTH) (r = -0.23, P = 0.0003) and serum phosphate (r = 0.16, P = 0.0119). No significant relationship was observed between serum calcium and 25-hydroxyvitamin D (r = 0.002, P = 0.98). Mean plasma PTH during clinical follow-up was 51% lower in patients with serum 25-hydroxyvitamin D > 60 nm when compared with patients who had 25-hydroxyvitamin D < 20 nm (P < 0.01).

Patients with PHP who have 25-hydroxyvitamin D levels > 60 nm have significantly reduced PTH hypersecretion when compared with patients with deficient vitamin D levels, without exhibiting worse hypercalcaemia.