Vitamin D is a fat-soluble steroid hormone that is required for the intestinal absorption of calcium, maintenance of calcium homeostasis, and protection against osteomalacia i.e. softening of the bones. Vitamin D deficiency can lead to loss of bone density which can contribute to osteoporosis (reduction in bone mass) and fractures in adults and rickets in infants and children. There is growing evidence indicating that low levels of Vitamin D may also be found in association with cardiovascular disease, diabetes, immune system diseases, microbial and respiratory diseases, cognitive impairment in older adults, mental health, and cancer.
Sunlight plays an essential role in Vitamin D production
Since skin exposure to sunlight (UV) plays an essential part in Vitamin D production, people who avoid exposure to the sun, have an increased risk of developing Vitamin D deficiency e.g. indoor occupations, housebound people, elderly in high care, or when skin is covered for religious or cultural reasons. Also, patients with signs, symptoms and/or planned treatment for various conditions might be at risk: (1) osteoporosis or osteomalacia, (2) increased alkaline phosphatase with otherwise normal LFTs, (3) hyperparathyroidism, hypo- or hypercalcemia, or hypophosphatemia, (4) malabsorption (i.e. CF, IBD & coeliac), (5) patients with medications known to decrease vitamin D levels (i.e. anticonvulsants) and (6) CRF and transplant recipients.
Forms of Vitamin D
There are two forms of vitamin D, D2, and D3. D3 (90%) is produced mainly photochemically in the skin when exposed to sunlight, and both D3 and D2 can also be sourced from diet or supplements. D2 and D3 are further hydroxylated in the liver to produce the prohormone 25 Hydroxyvitamin D3 (25-OHD). 25OHD is needed for the production of the active hormone 1,25-dihydroxyvitamin D3 (1,25D). 1,25D maintains the essential calcium balance in the body and is formed by hydroxylation of 25-OHD in the kidneys.
1,25D, the active form of vitamin D, has a very short half-life in the serum (T1/2 is 8 hours) and is highly regulated through parathyroid hormone (PTH). 25-OHD, the prohormone, on the other hand, has the highest affinity for vitamin D binding protein and highest concentration in the serum. 25-OHD is stable with a long half-life (T1/2 22-30 days) and is not affected by changes in PTH or Calcium. The prohormone 25-OHD is the metabolite that best assesses overall Vitamin D status; “Total 25-OHD” is the sum of 25-OHD3 + 25-OHD2.
ELITechGroup’s Vitamin D reagent
ELITechGroup Clinical Chemistry vitamin D reagent measures “Total 25-OHD” i.e. both D2 and D3 are measured equally. It is a particle-enhanced (Latex) immunoturbidimetric assay (PEITA) that enables routine Vitamin D testing to be performed on a standard clinical chemistry system like Selectra. The PEITA Vitamin D method doesn’t require specialized equipment or operators like LC-MS/MS, and improves laboratories’ efficiency in workflow compared to ELISA assays. The method is traceable to international standards (calibrators and trueness control traceable to SRM972) and benchmarked against LC-MS/MS gold standard reference method. It’s certified by CDC Vitamin D standardization Certification program (VDSCP), and also meets the criteria set by DEQAS advisory panel. Further, the assay is USA FDA 510(k) approved, USA CLIA classified and CE-IVD certified.
ELITechGroup Clinical Chemistry Vitamin D reagents are ready-to-use liquid stable with a broad measuring range and 28 days on board reagent stability. Additional to the short turnaround time (<10 minutes) compared with CLIA methods, there’s no requirement to dilute high samples or use additional collection tubes which provide cost and workflow efficiency to the laboratory.