Dr. John Cannell of the Vitamin D Council recommends that people wishing to test their levels of D3 request a 25-hydroxy-vitamin D blood test. He warns that many doctors will automatically order a test for activated vitamin D (1, 25-di-hydroxy-vitamin D or calcitriol) levels, but that calcitriol levels should never be used to determine adequate D3 levels because calcitriol is often elevated in cases of vitamin D deficiency. If your doctor insists on ordering an activated vitamin D test, find another doctor.

However, the limitations of the current technology make even the 25-hydroxy-vitamin D blood test unreliable. (Different laboratories report different results from the same specimen of blood. The same laboratory will often report significantly different levels from the same specimen of blood at different times.) In general, low numbers are more reliable than high numbers because interfering substances can easily give falsely elevated results.

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One of the more reliable testing facilities is the Endocrine Laboratory in the Clinical Chemistry Department of Charing Cross Hospital (Fulham Palace Road, London, W6 8RF % 0208 383 3645), but this service may only be accessed via your GP. The laboratory considers blood serum 25-hydroxy-vitamin D levels below 25 nanomoles per litre (umol/L) to be D3 deficient, levels between 25 and 50umol/L to be insufficient, and levels between 50 and 75umol/L to be sufficient. Levels above 75umol/L are rare unless the patient is taking D3 supplements.

We also recommend the Biolab Medical Unit, which charges £42 (2010) for a 25-hydroxy-vitamin D test. The test may be carried out by post but, again, it must be done via your GP or a registered practitioner.

For more information please contact Biolab Medical Unit, The Stone House, 9 Weymouth Street, London W1W 6DB
Tel: (+44) 020 7636 5959/5905
email: reception@biolab.co.uk

The laboratory is open from 9am to 5:30pm every weekday (excluding public holidays)

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