Vitamin D deficiency is a prevalent condition in humans as a result of the inclination to live in indoor settings. Recent advances in laboratory medicine have resulted in replacement of immunoassay methods by LC-MS/MS measurement techniques, which represent the current reference method. However, serum matrix effect resulting in an interference effect may lead to erroneous results in LC-MS/MS. In this study, our aim was to examine the interference of radionuclide molecules used for PET-CT imaging on vitamin D measurements.\\r\\nFor this purpose, 40 ?L of 18F-FDG was added into the control solution consisting of 100 micro-liter (?L) of vitamin D and 25(OH)D measurements were performed at 0 and 60 minutes using LC-MS/MS. Based on the measurements, radioactivity caused by positrons emitted from FDG was found to cause interference on 25(OH)D measurements depending on the elimination half-life. It has been concluded that the interference observed was caused by the radioactivity emitted from radionuclide molecules used in PET-CT imaging rather than the molecular mass of 25(OH)D.\\r\\nIn daily practice, elevated 25(OH)D levels bears clinical significance, particularly with respect to detection of the etiology of hypercalcemia in cancer patients. On the other hand, in patients undergoing PET-CT imaging, interference caused by FDG may lead to overestimation of vitamin D levels, even when measurements with the reference method LC-MS/MS are used; this may direct the clinician away from a diagnosis of bone metastasis. Therefore, detection of hypervitaminosis D after PET-CT imaging should raise a suspicion of interference.

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