Vitamin D-25 Hydroxy is ordered when an individual has low calcium and/or symptoms of vitamin D deficiency. This can appear as bone weakness/softness, or fractures in adults, or as rickets (bone malformation) in children.
The vitamin D test is for individuals at high risk of deficiency. It is used to monitor diseases that interfere with fat absorption. These diseases include cystic fibrosis or Crohn disease. This test also monitors the effectiveness of vit D, calcium, magnesium or phosphorus supplementation.
Individuals at risk of vitamin D deficiency include: older adults, individuals who have limited exposure to sunlight, individuals who are obese, or who have fat malabsorption.
Low levels of D-25 hydroxy are one of the earliest changes that show in individuals with early kidney failure. People with kidney disease also show low levels.
High levels of D-25 hydroxy show due to diseases that can make vit D outside of the kidneys. The two primary diseases related to this are sarcoidosis or certain lymphomas.
Long term high levels of vitamin D can eventually lead to the damage of certain organs such as the kidneys and blood vessels via calcification. If magnesium levels are low, a physician may supplement both magnesium and calcium in order to eliminate a low calcium level that is resistant to vit D.