FOR BLOOD TESTS TO BE EFFECTIVE YOU MUST NOT HAVE ELIMINATED GLUTEN FROM YOUR DIET!!!
Serological or blood tests are used to screen potential patients with gluten intolerance who are then referred to endoscopy, an examination recognized in the medical world as the “gold standard” for establishing the diagnosis. of celiac disease.
The set of serological tests usually includes:
- Anti-gliadin IgA and IgG (indicates if you have gluten sensitivity)
- Anti-transglutaminase (tTg) and/or anti endomysium (EMA) (indicates if you have gut damage)
- Total IgA (indicates if you have a selective IgA deficiency, which would compromise the validity of negative tests based on IgA)
What do serological tests tell us?
The first serological marker used to establish the diagnosis of celiac disease was the anti-gliadin antibody (AGA) class IgG (immunoglobulin type G). Although sensitive, this antibody is also apparently found in other diseases and is therefore not considered specific to celiac disease. Anti-gliadin antibody class IgA (immunoglobulin type A) is more specific but about 2% of patients with celiac disease have selective IgA deficiency. A combined anti-gliadin IgG and IgA test offers optimum sensitivity and specificity. If the anti-gliadin IgG test alone is positive, the total IgA test should be performed to assess whether a selective IgA deficiency is present.
Having a positive result for an anti-transglutaminase (tTG) or anti-endomysium (EMA) test means a very high probability (90-95%) that villous atrophy will be found during a biopsy of the small intestine. However, a negative result by no means eliminates the possibility of having celiac disease, it just makes it a little less likely.
Because a positive anti-tTG result is a strong indicator of intestinal damage, the trend seems to be away from using the anti-gliadin antibody test. Indeed, to save costs, the set of tests is often reduced to the simple anti-tTG test. Many “experts” consider gliadin antibodies optional and outdated. They say that anti-gliadin antibodies are not specific to celiac disease, but these antibodies are often the first to appear and are very significant in people with gluten sensitivity manifesting as a neurological disease, for example. The optimal strategy is to combine the search for anti-gliadin IgG and IgA antibodies as well as anti-tTg IgA.
Request a total IgA test if the AGA IgG test is not available as you may have IgA deficiency (present in 2-3% of celiacs) and the consequence could be that any negative results are actually false negatives.
It is also possible to have celiac disease or seronegative gluten sensitivity (negative serological tests).
Do I need a biopsy?
For a “gold standard” diagnosis, the answer is: yes you need the biopsy. But, if for you a diagnosis respecting the “gold standard” is not important, nobody forces you to have a biopsy if you do not want it. Many people are happy that the answer to the diet speaks for itself. Others want a solid diagnosis before adhering to a strict diet that will last a lifetime. Most, but not all, doctors recommend a biopsy to confirm the diagnosis.
One thing is certain, if you plan to request a biopsy, it must be done before starting the gluten-free diet. If you have already removed gluten from your diet, the biopsy may not be meaningful.
A biopsy may also be important to rule out other co-existing conditions that may be contributing to your symptoms. So if your symptoms do not improve with your change in diet, a biopsy may also be done at a later date to investigate these other possible conditions.
Some doctors will diagnose celiac disease based on positive blood results and/or resolution of symptoms following gluten withdrawal. A positive anti-tTG result, for example, is a very strong indicator that damage will be found on biopsy. So strong, in fact, that some physicians have begun to question the necessity, in such cases, of carrying out an invasive examination such as endoscopy to perform a biopsy.
Whether or not you want proof of celiac disease based on the biopsy is primarily a personal decision.