Omega-3 index

Laboratories print bands rather than a single range; many describe below 4% as the lowest band, 4 to 8% as the middle band and 8% and above as the highest. Ranges differ between methods.

The omega-3 index is the percentage of the fatty acids in red blood cell membranes that are the two main omega-3 fats, EPA and DHA, the ones found in oily fish. Because red cells live for about three months, the figure reflects the average intake of these fats over that time rather than what was eaten yesterday.

It is mainly offered by private testing services for people interested in their intake of omega-3 fats from fish and supplements. It is rarely requested on the NHS.

• Eating oily fish regularly
• Fish oil or algal omega-3 supplements
• Being older, in the general population

• A diet low in oily fish
• Being overweight
• Smoking
• A diet very high in omega-6 vegetable oils

• It reflects diet over about three months, so a recent change in eating will not show for some weeks
• Methods differ between laboratories

No fasting needed. A single result reflects the previous three months of diet; if it is repeated, a gap of at least three months is needed to see a change.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.