Endomysial antibody

The expected result is Negative. Some laboratories report a titre for a positive result. Like the tTG test it relies on IgA, so it reads falsely negative in people who make very little IgA.

Endomysial antibodies are antibodies, of the IgA class, that react with the connective tissue around smooth muscle fibres. They are directed against the same enzyme, tissue transglutaminase, as the tTG test, but are detected by a different method: the laboratory looks for a glow on a slide of tissue under a fluorescent microscope. It is reported simply as positive or negative.

Doctors request it as a follow-on test to confirm a positive tissue transglutaminase antibody result when looking at coeliac disease, particularly in children, where a strongly positive tTG together with a positive EMA can sometimes replace a gut biopsy.

• Coeliac disease, in someone eating gluten
• Dermatitis herpetiformis, the skin form of coeliac disease

• A gluten-free diet, which makes the test negative over months even in coeliac disease
• Negative is the usual finding in healthy adults
• Low IgA, which makes the test read falsely negative

• A negative result means little if gluten has been cut out of the diet before the test
• Selective IgA deficiency makes the test falsely negative
• Reading the slide depends on the person doing it, so a weak positive may be reported differently by two laboratories

No fasting needed, but gluten must have been eaten regularly for at least six weeks before the sample. It is read alongside the tTG antibody and total IgA from the same sample and is not usually repeated once the answer is known.

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