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Relationship between vitamin D, calcium and parathyroid hormone in Cape Town
  1. D Haarburger,
  2. M Hoffman,
  3. R T Erasmus,
  4. T S Pillay
  1. Division of Chemical Pathology, Groote Schuur Hospital, University of Cape Town and Department of Chemical Pathology, University of Stellenbosch, Tygerberg Hospital, and National Health Laboratory Service, Cape Town, South Africa
  1. Professor T S Pillay, Division of Chemical Pathology, University of Cape Town, Private Bag X3, Observatory, Cape Town, South Africa; profts.pillay{at}


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.