Toggle: English / Spanish DefinitionThe 25-hydroxy vitamin D test is the most accurate way to measure how much vitamin D is in your body.In the kidney, 25-hydroxy vitamin D changes into an active form of the vitamin. The active form of vitamin D helps control calcium and phosphate levels in the body.This article discusses the blood test used to measure the amount of 25-hydroxy vitamin D.Alternative Names25-OH vitamin D test; 25-hydroxycholecalciferol testHow the Test is PerformedA blood sample is needed. How to Prepare for the TestUsually you will not need to fast. However, this depends on the laboratory and the testing method used.How the Test Will FeelWhen the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing.Why the Test is PerformedThis test is done to determine if you have too much or too little vitamin D in your blood.Normal ResultsThe normal range of vitamin D is measured as nanograms per milliliter (ng/mL).
Many experts recommend a level between 20 and 40 ng/mL. Others recommend a level between 30 and 50 ng/mL.The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some laboratories use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results, and whether you may need vitamin D supplements.What Abnormal Results MeanLower-than-normal levels can be due to a vitamin D deficiency, which can result from:Lack of exposure to sunlightLack of enough vitamin D in the dietLiver and kidney diseasesPoor food absorptionUse of certain medicines, including phenytoin, phenobarbital, and rifampin Low vitamin D levels are more common in African-American children (especially in the winter), as well as in infants who are breastfed only. Low vitamin D levels have also been associated with an increased risk of developing cancer. For more information, see the article on vitamin D deficiency.
Higher-than-normal levels may be due to excess vitamin D, a condition called hypervitaminosis D.RisksVeins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.Other risks associated with having blood drawn are slight but may include:Excessive bleedingFainting or feeling light-headedHematoma (blood accumulating under the skin)Infection (a slight risk any time the skin is broken)ReferencesDawson-Hughes B, Mithal A, Bonjour JP, et al. IOF position statement: vitamin D recommendations for older adults. Osteoporosis Int. 2010;21:1151-1154.Dietary Reference Intakes for Calcium and Vitamin D: Institute of Medicine Brief Report. www.iom.edu/Reports/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D/Report-Brief.aspx Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline.
This site cannot be accessed from your current location. or click here to register.Assay Principle:Diazyme's Enzyme-Immunoassay FemtoQuant™ 25-Hydroxy Vitamin D test is based on the principle of α-complementation of the enzyme β-galactosidase and the competition between an enzyme donor-25-OH Vitamin D conjugate, an anti-Vitamin D antibody and the 25-OH Vitamin D content of a serum sample. Samples with higher 25-OH Vitamin D concentrations produce higher β-galactosidase activities and vice versa. A nitrophenyl-ß- galactoside derivative (NPG) is used as the enzyme substrate. The reaction's product has maximum absorbance at 415 nm. The 25-OH Vitamin D concentration of a sample is proportional to the measured β-galactosidase activity.Diazyme 25-OH Vitamin D for Clinical Chemistry Analyzers Kit Configuration:Diazyme's Vitamin D assay kit contains 1 sample diluent and 3 liquid stable reagents and calibrator set. The intended use is for the quantitative determination of 25-(OH) D levels in serum or plasma, on automated chemistry analyzers, and for the assessment of Vitamin D sufficiency.
Assay Features:Multiple instrument options availableReagent kit, calibrator and control sets offered separatelyLiquid Stable formatMinimal sample of only 20 μL needed15-19 minutes to first resultReport total 25-OH Vitamin D (D2+D3)No off-line sample pretreatment neededExcellent Correlations to LC-MS/MS and leading 25-OH Vitamin D ImmunoassaysCost effectiveAssay Procedure:The assay procedure for the Roche Modular P chemistry analyzer is shown below: Specimen calibrator, control and samples are first diluted onboard: 20 μL of serum which is then diluted with 155 μL of diluent. Once diluted an additional 20 μL of the diluted specimen is then used for analysis.Assay Accuracy:The performance of this assay was compared to the performance of a legally marketed 25-OH Vitamin D enzyme immunoassay. The results for 98 serum samples are shown in the table below:Deming Regression Analysis95% Confidence IntervalSlope1.005 (0.969 to 1.041)Intercept-0.21 (-2.15 to 1.73)Correlation Coefficient0.984 (0.976 to 0.989)Range9.5-140.9Assay Linearity:Eleven levels of linearity were prepared by diluting a high serum sample with Vita-min D-depleted serum.