Test Details & Preparation
A vitamin D3 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 help monitor the health status of individuals with diseases that interfere with fat absorption, such as cystic fibrosis and Crohn’s 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 and help determine the effectiveness of treatment when vitamin D, calcium, phosphorus, or magnesium supplementation is prescribed.
A vitamin D3 test is ordered when calcium is low 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.
A vitamin D3 test is also 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, or who have fat malabsorption are at an increased risk of a vitamin D deficiency.
A low blood level of 25-hydroxy vitamin 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.
A high level of 25-hydroxyvitamin D usually reflects excess supplementation from vitamin pills or other nutritional supplements.
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 parathyroid hormone or when there are diseases, such as sarcoidosis or some lymphomas that can make 1, 25-dihydroxyvitamin D outside of the kidneys.