Vitamin D 25 (OH) D Testing

Related Subjects: | Vitamin D Replacement | Osteomalacia-Rickets-Vitamin D | Vitamin D resistant rickets | Vitamin D (25 OH D) Testing | X linked Hypophosphataemic rickets | Osteoporosis

Used to screen for Osteomalacia/Rickets. Vitamin D replacement is appropriate for deficiency < 30 nmol/L. Those with higher levels of treatment may be appropriate in some patients. There has been a change in guidance. Routine testing of Vitamin D should NOT be undertaken.

About

• Most assays measuring vitamin D test the biologically inactive form, 25-(OH)-Vitamin D, as it is the major form of vitamin D in circulation.
• The active metabolite, 1,25-OH-Vitamin D, has a circulating half-life of 4 to 6 hours, making it difficult to accurately interpret.
• Vitamin D deficiency is defined by a 25-(OH)-Vitamin D level < 20 ng/mL, and insufficiency as a level between 21 to 29 ng/mL.
• Normal vitamin D levels range from 30 to 100 ng/m

Do not measure 1,25(OH)D as it may be falsely normal or high, has a short half life and is a 1/1000 concentration as 25(OH)D and is less than useless. Measure 25(OH)D

When to check vitamin D level

• The patient has one or more of the following clinical features
  • Widespread or localised bone pain and tenderness
  • Children bone deformity, reluctance to weight bear, impaired growth
  • Proximal muscle weakness, i.e. quadriceps and glutei. Difficulty rising from a chair or a waddling gait.
  • Swelling, tenderness and redness at pseudo-fracture sites
  • Fractures, typically femoral neck, scapula, pubic rami, ribs or vertebrae
  • Non-specific myalgia, especially with a raised creatinine kinase (CK)
  • Myalgia on the prescription of a statin
• And the patient has one or more of the following risk factors
  • Black and ethnic minority patients with darker skin
  • Elderly patients in residential care or housebound
  • Intestinal malabsorption, for example cystic fibrosis, coeliac disease,
  • Inflammatory bowel disease, gastrectomy or bariatric surgery, radiation enteritis
  • Routine covering of face or body, for example wearing a veil or habitual sunscreen use
  • Vegan or vegetarian diet, Liver or renal disease
  • Medications including cholestyramine, rifampicin, glucocorticoids, antiretrovirals
  • Pregnant and lactating women, Obesity (BMI >30)
• Check you have excluded other causes
  • Myeloma, Rheumatoid arthritis
  • Polymyalgia rheumatica, Hypothyroidism
• Other clinically appropriate indications for measuring vitamin D include
  • Older patients with a history of falls
  • Bone disease that may be improved with vitamin D treatment or where correcting vitamin D before treatment is appropriate
  • Before commencing Zoledronic acid or Denosumab
  • Unexplained high ALP, Low Phosphate or calcium or raised PTH
  • Before thyroidectomy or bariatric surgery
  • Anticonvulsant treatment (NICE guidelines recommend check every 2 - 5 years).
  • At initial diagnosis in patients with multiple sclerosis
• Sample requirements
  • If the patient is on high dose biotin therapy (>5 mg/day), collect the sample at least 8 hours after the last dose.
  • Adults, blood taken into a 5mL gold top tube
• Interpretation of 25-Hydroxyvitamin D (vitamin D)