VITAMIN D 25 - HYDROXY

Two forms of Vitamin D can be measured in the blood, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D. The 25-hydroxyvitamin D is the major form circulating in the bloodstream and the Vitamin D 25-Hydroxy test measures blood levels of 25-hydroxyvitamin D. 

This test is useful for the diagnosis of Vitamin D deficiency and Hypervitaminosis D. It is also used for diagnosis of causes of Rickets & Osteomalacia and for monitoring Vitamin D replacement therapy. 

Your doctor may request a Vitamin D 25-Hydroxy test in the following conditions: 

• Abnormal calcium, phosphate, and/or parathyroid hormone (PTH) concentration in the blood. 
• Certain types of bone disease or muscle weakness/pain. 
• Gastrointestinal tract disease 
• If a person is on certain anticonvulsant drugs 
• If a person is experiencing symptoms of a Vitamin D deficiency such as  
  • Weakening of the bones 
  • Abnormal bone development 
  • Bone deformity 
  • Bone pain 
  • Muscle weakness or cramps 
  • Seizures 
  • Dental abnormalities 

However, screening may be done on people who are at high risk for Vitamin D deficiency, such as those who: 

• Are over the age of 65  
• Are obese (or have lost weight from bariatric surgery) 
• Are on certain medicines 
• Have osteoporosis or thin bones 
• Have limited sun exposure 
• Have problems absorbing vitamins and nutrients in their intestines, such as those with ulcerative colitis, Crohn’s disease, or celiac disease 

A healthcare professional will draw a blood sample from a vein in the arm or a finger-prick or heel-prick (newborns). There are no special preparations required for Vitamin D 25-Hydroxy test, though your doctor may instruct you if any specific preparations are required for the test. 

Vitamin D 25-Hydroxy test is a safe, standard test and there are minimal risks involved such as 

• Bleeding 
• Light headedness 
• Infection 
• Bruising 

The Vitamin D 25-Hydroxy test results are usually measured in nanomoles per liter (nmol/L). The normal value ranges may vary slightly among different laboratories.  

The doctor will evaluate the results based on health, gender, age, and other factors. 

The table below represents a reference range and interpretations based on the test results: 

Level                                    Reference Range (nmol/L)                 Interpretation 

Deficient                             < 50                                                   Vitamin D levels are too low to support healthy bodily
                                                                                                      functions. High risk for developing bone disease. 

Insufficient                          50-74                                                Vitamin D levels are lower than the ideal reference range. 

Sufficient                            75-250                                               Vitamin D levels fall within the reference range 

Potential intoxication         > 250                                                 Excessive amount of vitamin D in the body. High risk for toxic
                                                                                                      effects.