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How is vitamin D deficiency diagnosed?

A low vitamin D level can be diagnosed with a blood test called 25 hydroxyvitamin D or 25OHD (OH = hydroxy, D = vitamin D). Although there is no formal definition of vitamin D deficiency, some groups use the following values in adults:

  • A normal level of vitamin D is defined as a 25OHD concentration greater than 30 ng/mL (75 nmol/L).
  • Vitamin D insufficiency is defined as a 25OHD concentration of 20 to 30 ng/mL (50 to 75 nmol/L).
  • Vitamin D deficiency is defined as a 25OHD level less than 20 ng/mL (50 nmol/L).