Specimen Requirements

Alternate Specimen Requirements

Minimum Specimen Requirements

Stability

Days Performed

Mon - Sat

Turnaround Time

1 - 3 days

Methodology

Clinical Info

Vitamin D is crucial to bone health, calcium metabolism, and overall well-being. Although sunlight exposure to skin may provide adequate levels of vitamin D, minimal or no sun exposure and low dietary vitamin D intake commonly results in hypovitaminosis D (vitamin D deficiency). 25-Hydroxy vitamin D [25(OH)D], the principal circulating form of vitamin D in plasma, is the most reliable measure of overall vitamin D status even though it is biologically inactive. Testing for 25(OH)D is useful in ruling out vitamin D deficiency as a cause of hypocalcemia, rickets, or osteomalacia, as well as in securing a differential diagnosis of hypercalcemia that could be indicative of excess parathyroid hormone, sarcoidosis, some forms of lymphoma, or other disorders. Testing for 25(OH)D is also useful in diagnosing intestinal malabsorption and vitamin D deficiency or intoxication, including the following: distinguishing between vitamin D-dependent and vitamin D-resistant rickets, monitoring the vitamin D status of patients with chronic renal failure, and monitoring therapeutic response in patients being treated for vitamin D-related disorders. Decreased 25-hydroxy vitamin D levels indicate an insufficiency or deficiency due to poor diet, decreased exposure to the sun, malabsorption of vitamin D, or liver and kidney diseases. When associated with hypercalcemia, there may be hypersensitivity to vitamin D, as in sarcoidosis.

Clinical Limitation

Values of 25-hydroxy vitamin D can vary with exposure to sunlight, which may be affected by the season of the year and geographic location. There are also variations depending on skin pigmentation, age, and during menstrual cycles, particularly at the time of ovulation. Because of the complex nature of calcium balance, it may also be useful to measure parathyroid hormone in conjunction with vitamin D.