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Test Name:
Vitamin D, 1,25-Dihydroxy
- SBMF No:
30134 - Performance Lab Name:
Manual Lab - Test Mnemonic:
VIT D 1 25 - ABN:
Not required - CPT Code:
82652 - LOINC Code:
1649-3 - Also Known As:
Calcitriol
1,25-Dihyroxyvitamin D
1,25-Dihyroxy D
1,25 diOH Vitamin D - Also See:
30054 – Vitamin D, 25-Hydroxy - Spec Type:
Serum - Spec Container:
Gold top (SST) or red top (serum) tube - Alt Spec Type:
Plasma - Alt Spec Container:
Lavender top (EDTA) tube - Pref Vol:
2.0 mL - Min Vol:
1.0 mL - Fasting:
No - Spec Collect:
Routine venipuncture - Spec Process:
Serum sample tubes, clot 30 minutes
Promptly centrifuge 15 minutes
Immediately transfer serum or plasma to separate plastic tube - Spec Store Transport:
Refrigerated (72 hours) or frozen - Spec Stability:
3 days room temperature (20-30°C)
3 days refrigerated (2-8°C)
6 months frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles - Methodology:
Radioimmunoassay (RIA) - Use:
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.
- Clinical Significance:
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.
- Reference Range:
38-88 pg/mL - Day Run:
Sun, Tue, Thu - Time Run:
8:00 am - Time Reported:
5:00 pm, next day - Test Type:
CHEMISTRY
