Aim: The aim of this study was to test the hypothesis that vitamin D deficiency is associated with abnormal levels of calcium and parathyroid hormone (PTH).
Methods: Vitamin D requests at a tertiary hospital in South Africa over 2 years were retrospectively analysed along with calcium and PTH levels.
Results: Only when the 25-hydroxyvitamin D (25(OH)D) level dropped below 25 nmol/l, was there a significant rise in PTH. A subnormal 25(OH)D level was also not always related to hypocalcaemia, as more than half of patients with their 25(OH)D level below 25 nmol/l had calcium levels in the reference range. However, all patients with calcium levels below 1.8 mmol/l were shown to have vitamin D insufficiency.
Conclusion: Hypovitaminosis D may co-exist with a blunted PTH response. Therefore, assumptions about vitamin D status should not be made based on PTH and calcium values. 25(OH)D measurements should be requested when vitamin D deficiency is clinically suspected, irrespective of biochemical results.
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Competing interests: None.
Funding: National Health Laboratory Service, Cape Town, South Africa.
Ethics approval: Ethics approval was obtained.