Newcastle Laboratories

Vitamin D, total, (includes 25-hydroxy cholecalciferol and 25-hydroxy ergocalciferol), serum

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 kid...

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.

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Test Details

  • Discipline:

    Biochemistry

    Biochemistry

  • Specimen Container Adult:

    Serum

    Serum

  • Specimen Container Paediatric:

    Serum

    Serum

  • Minimum Volume Adult:

    1 mL blood

    1 mL blood

  • Minimum Volume Paediatric:

    1 mL blood

    1 mL blood

  • Special Requirement:

    Fasting recommended but not required.
    N.B. Total vitamin D assay detects 25-hydroxy cholecalciferol and 25-hydroxy ergocalciferol.

    Fasting recommended but not required.
    N.B. Total vitamin D assay detects 25-hydroxy cholecalciferol and 25-hydroxy ergocalciferol.

  • Sample Stability:

    Unseparated: 3 days

    Separated:

    - 8 hours at 15-25C

    - 4 days at 4-8°C

    - 24 weeks at -20C

    Unseparated: 3 days

    Separated:

    - 8 hours at 15-25C

    - 4 days at 4-8°C

    - 24 weeks at -20C

  • Transport Requirements:

    Ambient

    Ambient

  • Reference Ranges:

    Paediatric: As adult at birth, rising to c. 1.5 - 2 x adult between c. 1m and 3y. Similar to adult from 4y.

    Adult:

    Less than 25nmol/L - Vitamin D deficiency, consider treatment

    25-50nmol/L - Vitami...

    Paediatric: As adult at birth, rising to c. 1.5 - 2 x adult between c. 1m and 3y. Similar to adult from 4y.

    Adult:

    Less than 25nmol/L - Vitamin D deficiency, consider treatment

    25-50nmol/L - Vitamin D may be insufficient. Consider supplementation and dietary and lifestyle changes

    Greater than 50nmol/L - Vitamin D sufficiency

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  • Factors Affecting Result:

    Heterophilic antibodies can interfere with immunoassays.

    Heterophilic antibodies can interfere with immunoassays.

  • Routine Contact Name:

    Duty Biochemist

  • Routine Telephone:

    Freeman: 0191 244 8889

    RVI: 0191 282 9719

    Freeman: 0191 244 8889

    RVI: 0191 282 9719

  • Routine Email:

Availability:

Available during full access hours.

Site of analysis: FRH and RVI

Turn Around:

Within 2 full access days

Send To:

Department of Blood Sciences – Freeman Hospital

Freeman Hospital
Freeman Road
Newcastle upon Tyne
NE7 7DN

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