Turnaround times
The quoted turnaround time is from sample receipt in the laboratory, to results authorisation in the Laboratory Information Management system. The times do not include transport of specimen to the laboratory or the administrative process to print and post/email reports. Service users must allow for transport and reporting time when ordering tests.
Clinical background:
Vitamin D is a fat-soluble steroid hormone precursor that is mainly produced in the skin by exposure to sunlight. Vitamin D is biologically inert and must undergo hydroxylation in the liver and kidney to become the biologically active 1,25-dihydroxyviatmin D. The two important forms of Vitamin D are vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). In contrast to vitamin D3, the human body cannot produce vitamin D2 which is present in fortified food or given by supplements. In human plasma vitamin D2 and D3 are bound to the vitamin D binding protein and transported to the liver where both are hydroxylated to form vitamin D 25-OH, i.e. 25-OH vitamin D. 25-OH vitamin D is widely regarded as the best indicator to determine the overall vitamin D status as it is the major storage form of vitamin D in the human body. This primarily circulating form of vitamin D is biologically inactive with levels approximately 1000-fold greater than the circulating 1,25-dihydroxyvitamin D. The half-life of circulating 25-OH vitamin D is 2-3 weeks. More than 95% of 25OH-vitamin D, measurable in serum, is 25OH-vitamin D3, where as 25OH-vitamin D2 reaches measurable concentrations only in patients taking vitamin D2 supplements.
Vitamin D is essential for bone health. In children, severe deficiency leads to bone-malformation, known as rickets. Milder degrees of insufficiency are believed to cause reduced efficiency in the utilization of dietary calcium. Vitamin D deficiency causes muscle weakness; in the elderly, the risk of falling has been attributed to the effect of vitamin D on muscle function. Vitamin D deficiency is a common cause of secondary hyperparathyroidism. Secondary hyperparathyroidism, especially in elderly vitamin D deficient adults can result in osteomalacia, increased bone turnover, reduced bone mass and risk of bone fractures. Low 25OH-vtamin D concentrations are also associated with lower bone mineral density. In conjunction with other clinical data, Vitamin D measurement may be used as an aid in the assessment of bone metabolism.
Specimen container paediatric:
Serum
Specimen container adult:
Serum
Minimum volume paediatric:
0.5 mL
Minimum volume adult:
1 mL blood
Sample stability:
Unseparated:
3 days
Separated:
– 8 hours at 15-25C
– 4 days at 4-8°C
– 24 weeks at -20C
Transport requirements:
Ambient
Reference ranges:
<25 nmol/L – vitamin D deficient
25-50 nmol/L – vitamin D may be insufficient
>50 nmol/L – vitamin D sufficiency