Product Description
This tests includes a 25-OH-Vitamin D test.
A vitamin D test is used to:
Determine if bone weakness, bone malformation, or abnormal metabolism of calcium (reflected by abnormal calcium, phosphorus, PTH) is occurring as a result of a deficiency or excess of vitamin D. Help diagnose or monitor problems with parathyroid gland functioning since PTH is essential for vitamin D activation. Screen people who are at high risk of deficiency, as recommended by the National Osteoporosis Foundation, the Institute of Medicine, and the Endocrine Society. Help monitor the health status of individuals with diseases that interfere with fat absorption, such as cystic fibrosis and Crohn disease, since vitamin D is a fat-soluble vitamin and is absorbed from the intestine like a fat Monitor people who have had gastric bypass surgery and may not be able to absorb enough vitamin D. Help determine the effectiveness of treatment when vitamin D, calcium, phosphorus, and/or magnesium supplementation is prescribed
When is it ordered?
When calcium is low and/or a person has symptoms of vitamin D deficiency, such as bone malformation in children (rickets) and bone weakness, softness, or fracture in adults (osteomalacia), 25-hydroxyvitamin D usually is ordered to identify a possible deficiency in vitamin D.
The test may be requested when an individual is known to be at risk of vitamin D deficiency. Older adults, people who are institutionalized or homebound and/or have limited sun exposure, those who are obese, who have undergone gastric bypass surgery, and/or who have fat malabsorption are at an increased risk of a vitamin D deficiency. Also included in this group are people with darker skin and breastfed infants. 25-hydroxyvitamin D is often requested before an individual begins drug therapy for osteoporosis.
1,25-dihydroxyvitamin D
When calcium is high or a person has a disease that might produce excess amounts of vitamin D, such as sarcoidosis or some forms of lymphoma (because immune cells may make 1,25-dihydroxyvitamin D), 1,25-dihydroxyvitamin D usually is ordered. Rarely, this testing may be indicated when abnormalities of the enzyme that converts 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D or renal disease are suspected. When vitamin D, calcium, phosphorus, or magnesium supplementation is necessary, vitamin D levels are sometimes measured to monitor treatment effectiveness.
What does the test result mean?
Although there are differences among vitamin D methods, most laboratories utilize similar reference intervals. Because toxicity is rare, the focus has been on the lower limit and what cut-off for total 25-hydroxyvitamin D (D2 + D3) indicates deficiency.
The Endocrine Society defines vitamin D deficiency as a 25-hydroxyvitamin D blood level below 20 ng/mL (50 nmol/liter) and vitamin D insufficiency as a level between 21–29 ng/mL (52.5–72.5 nmol/liter).
The U.S. Institute of Medicine has concluded that a 25-hydroxyvitamin D level of 20 ng/mL (50 nmol/liter) or above is adequate for bone health, and that levels greater than 30 ng/mL do not offer significantly better effects. However, it is fair to say that the level of 25-hydroxyvitamin D associated with protection from the many other disorders recently associated with a lack of vitamin D is controversial.
25-hydroxyvitamin D
A low blood level of 25-hydroxyvitamin D may mean that a person is not getting enough exposure to sunlight or enough dietary vitamin D to meet his or her body’s demand or that there is a problem with its absorption from the intestines. Occasionally, drugs used to treat seizures, particularly phenytoin (Dilantin), can interfere with the production of 25-hydroxyvitamin D in the liver.
There is some evidence that vitamin D deficiency may increase the risk of some cancers, immune diseases, and cardiovascular disease.
A high level of 25-hydroxyvitamin D usually reflects excess supplementation from vitamin pills or other nutritional supplements.
1,25-dihydroxyvitamin D
A low level of 1,25-dihydroxyvitamin D can be seen in kidney disease and is one of the earliest changes to occur in persons with early kidney failure.
A high level of 1,25-dihydroxyvitamin D may occur when there is excess parathryoid hormone or when there are diseases, such as sarcoidosis or some lymphomas, that can make 1,25-dihydroxyvitamin D outside of the kidneys.
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