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Introduction: Studies about vitamin D [25(OH)D] stability in plasma are limited and preanalytical variables such as tube type may affect results. We aimed to evaluate effect of storage conditions, sample type and some preanalytical variables on vitamin D concentration. Materials and methods: Blood samples from 15 healthy subjects were centrifuged at different temperatures and stored under different conditions. Serum and plasma 25(OH)D difference, effect of centrifugation temperature and common storage conditions were investigated. Results: There was no difference between serum and plasma vitamin D concentration. Centrifugation temperature had no impact on vitamin D concentration. 25(OH)D is stable under common storage conditions: 4 hours at room temperature, 24 hours at 2-8 °C, 7 days at -20 °C, 3 months at -80 °C. Conclusion: Vitamin D does not require any special storage conditions and refrigeration. Both serum and plasma can be used for measurement. more...