A Study on the Biological Reference Interval of Vitamin D in North-East India

Introduction: Vitamin D is the generic name given to all steroids that exhibit the biological activity of Cholecalciferol and derived from 7-dehydrocholesterol. Vitamin D has a major role in maintenance of healthy bones and teeth, which are of considerable public health importance. Vitamin D is normally synthesised in the skin in adequately sun exposed individuals and a minor portion is derived from the diet. Deficiency of vitamin D is prevalent worldwide. Vitamin D levels range from 30-100 ng/mL in healthy individuals. The Indian population is being evaluated for vitamin D using Biological Reference Interval (BRI) derived from western studies. Aim: To evaluate the BRI set by two reagent manufacturers, Ortho Clinical Diagnostics and Biomerieux to assess whether they were adequate for the North-Eastern Indian population. Materials and Methods: The study consisted of 678 participants, comprising of healthy attendants accompanying patients presenting at two tertiary level super-speciality hospitals in Guwahati, Assam, India. Samples were collected all through one year, from July 2017 to June 2018. Both male and female participants were assessed for 25-hydroxy vitamin D levels by Chemiluminescence and Enzyme-linked Fluorescence techniques, the two most common techniques employed in the region. The values obtained were statistically analysed by unpaired Student’s t-test. The p-value<0.05 were considered statistically significant. Results: For 678 participants aged 1-82 years, BRI of vitamin D was observed to be 8.0-56.3 ng/mL, these values overlapped with data from both the reagent manufacturers’ studies. Only 241 (35.5%) participants were found to have vitamin D sufficiency (>30 ng/mL). In our study, we also found that vitamin D levels decreases with age, with highest levels in the age group 1-10 years and lowest levels in the geriatric age group (> 60 years age). Statistically significant difference was found between vitamin D levels between male and female participants (p<0.001). Conclusion: The vitamin D levels observed in the present study were in a range that was in between the ranges in the studies undertaken by the reagent manufacturers. Also, the values that we obtained were on the lower side. These observations shows that the criteria for defining the status of insufficiency and deficiency of vitamin D need to be further evaluated for the North-Eastern population.