Plasma

3 mL whole blood from light green top tube or TWO Microtainer^® devices for pediatric patients.

1 hour (upon receipt in laboratory)

Reference range in Epic: 20-80 ng/mL

Deficiency: Less than 20 ng/mL
Borderline: 20-29 ng/mL
Optimum level: 30-80 ng/mL
Possible toxicity: > 150 ng/mL

This is the appropriate screening test for routine assessment of vitamin D nutritional status. This assay accurately quantifies the sum of 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2. 25-Hydroxyvitamin D reference ranges are a controversial topic, with some authorities suggesting optimal concentrations should be 30 ng/mL or higher based on correlations of 25-hydroxyvitamin D plasma concentrations with physiological parameters such as parathyroid hormone or calcium concentrations.

Endocrine Society, Institute of Medicine (IOM), and World Health Organization (WHO) guidelines designate 25-hydroxyvitamin D plasma concentrations below 20 ng/mL as deficient, based on increased frequency of adverse outcomes (e.g., osteoporotic fractures). However, optimal 25-hydroxyvitamin D concentrations greater than 20 ng/mL may be considered for specific disease conditions. 25- Hydroxyvitamin D concentrations should be interpreted in context of clinical history and physical examination along with other laboratory studies, if indicated. For workup of hypercalcemia, vitamin D status in renal failure patients, and certain malignancies, "Vitamin D (1,25- dihydroxy)" may be indicated.

This assay may be significantly impacted by high-dose biotin (>5 mg dose) taken within previous 12 hours. High concentrations of biotin may lead to falsely increased results. These concentrations may be found in patients taking over-the-counter supplements with biotin content much higher than nutritional requirements for biotin. Specimens should not be collected until at least 12 hours after the last dose.

References
Endocrine Society Clinical Guidelines. J Clin Endocrinol Metab 96: 1911-1930, 2011.
Holick MF, NEJM 357: 266-281, 2007.
Krasowski MD, Am J Clin Pathol 136: 507-514, 2011.
Vieth R. Am J Clin Nutr 69:842-856, 1999.
Wharton B, Bishop N. Lancet 362:1389-1400, 2003.

This test is also performed in the Iowa River Landing (IRL) clinical laboratory (for specimens drawn at that site).

Avoid grossly hemolyzed specimens.

Electrochemiluminescence Immunoassay, Multiplex flow immunoassay

82306

See also:
Vitamin D (1,25 Dihydroxy), Serum

See Additional Information:
Biotin Interference with Immunoassays