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One vitamin D blood test said toxic the other said normal – Aug 2010

Vitamin D Toxicity?: A Case Study

New Zealand Journal of Medical Laboratory Science
Volume 64 Issue 2 (Aug 2010)
Khieng, Vichet1; Stevens, Catherine2
Abstract: One of vitamin D's important roles is body calcium regulation. Vitamin D deficiency can lead to hypocalcaemia, and consequently cause bone related disorders. On the other hand, prolonged excessive vitamin D can lead to hypercalcaemia, and consequently cause renal stones. Compared to vitamin D deficiency, vitamin D toxicity is very rare. We report a case where the patient was initially thought to be hypervitaminosis D. In our laboratory, we use the ECLIA method from Roche Diagnostic to measure serum vitamin D.

The patient had vitamin D levels of >250 nmol/L on more than one occasion whilst appearing to be clinically vitamin D deficient.

Furthermore, results for vitamin D levels on the same samples by another laboratory with a different assay method came back as low normal. We carried out investigations for possible immunoassay interference. We found that an interfering factor caused falsely high results in competitive assays and falsely low results in a sandwich assay. The sample was sent to Roche Diagnostics in Germany for further investigation. Roche Diagnostics was able to show that the interfering factor was to the solid phase, but did not identify the interfering factor.

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