VITAMIN D, 1,25 DIHYDROXY

Code
900.5580
Name
VITAMIN D, 1,25 DIHYDROXY
Category
None
Department
Send-Out
Start Date
Expiration Date
Synonyms
1,25-Dihyroxyvitamin D, 1,25-Dihyroxy D, Calcitriol
CPT Codes
82652
Site
SBMF
Reference Test
30134
ATLAS Test Code

Specimen Information

Type

Gold, SST

Volume

2.0 ml

Transport Info

Centrifuge and immediately transfer serum to separate plastic tube
Refrigerated

Fasting Required?
False
Patient Instructions

Reference Range

38-88 pg/mL

Methodology

Radioimmunoassay (RIA)

Clinical Significance

The circulating concentration of 25-hydroxyvitamin D is considered the barometer of vitamin D status and remains the best test to screen for Vitamin D deficiency.

1,25-dihydroxyvitamin D levels is decreased in hypothyroidism and chronic renal failure and is also helpful in differential diagnosis of hypercalcemia and in patients with hereditary deficiencies of 1-alpha-hydroxalase or end order resistance to 1,23-dihydroxyvitamin D. It can be elevated in sarcoidosis, some malignancies, as well as primary and physiologic hyperparathyroidism.

Vitamin D is a fat-soluble vitamin that consists of vitamin D3 (cholecalciferol) that is made in the skin via the action of sunlight exposure and vitamin D2 (ergocalciferol) that is obtained from the diet. Once in the circulation, both vitamin D2 and D3 are metabolized to 25-hydroxyvitamin D in liver. The 25-OH form of the hormone is the principle circulating reservoir in the plasma and is generally the best indicator of overall vitamin status. 25-OH vitamin D is further converted to 1,25-dihydroxyvitamin D in kidney, which is the biologically active form of the vitamin D. The production of 1,25-diOH vitamin D is tightly controlled by PTH and is important in the regulation of serum calcium homeostasis.

Decreased circulating availability of vitamin D can occur in persons with inadequate exposure to sunlight, dietary deficiency, or malabsorption. Vitamin D insufficiency and vitamin D deficiency are now recognized to be a significant cause of metabolic bone disease in older adults. The incidence may vary from 5-25% among independent elderly to 60-80% among institutionalized elderly depending upon latitude, nutrition, sun exposure, supplementation, degree of skin pigmentation, and sunscreen use. A yearly determination of vitamin D is suggested to be part of blood evaluation in elderly patients.

Although 1,25-dihydroxyvitamin D is the biologically active form of vitamin D, its level in the body does not provide more useful information about the patient's vitamin D status. As a person becomes vitamin D deficient, secondary hyperparathyroidism may be developing and resulting in increased production of 1,25-dihydroxyvitamin D.

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