Blood screening for gliadin antibodies
Immunoglobulins (Ig) are also known as antibodies and come in various classes including A, G and E. Gliadin antibodies were developed for screening for coeliac disease. The tests included are IgA gliadin and IgG gliadin . They have been superceded as a blood screen for coeliac disease by a blood test called tissue transglutaminase (tTG). More about tTG later. Gliadin antibody testing is still very useful in those with an immune response to gluten that is not coeliac disease.
IgA and IgG gliadin are antibodies against gliadin . Gliadin is a component of the protein gluten. Antibodies are formed as part of our immune defence so antibodies to gliadin are an immune response against gliadin or gluten. A low level of antibodies may be perfectly normal and beneficial but high levels are not. IgG gliadin is the test most commonly raised in those who have an immune response to gluten but do not have coeliac disease. The use of this test to diagnose an allergy to gluten is controversial as doctors have been taught that gluten cannot cause conditions other than coeliac disease, and some laboratories do not do these tests any longer. To arrange your blood tests see http://www.doctorgluten.com/cms/index.php/Gluten-levels/New-to-Gluten/Why-you-need-the-blood-tests.html Do not stop eating gluten until after you have the test results and have had them interpreted.
Blood screening for coeliac disease
Tissue transglutaminase (tTG) is a test that looks for damage in the small bowel. An alternative is endomysial antibody (EMA). tTG and EMA are IgA based tests so total immunoglobulins should be ordered also to make sure that the person isn't deficient in IgA. It is impossible for IgA gliadin, tTG or EMA to be raised, if the person doesn't make enough IgA in general. If the tTG or EMA is positive, a small bowel biopsy is done to confirm coeliac disease.
Blood screening for conditions related to gluten
If your doctor thinks that you need testing for a gluten allergy or Coeliac Disease, it may also be appropriate to add some other tests. Discuss your symptoms with your doctor and let them know your concerns. The sort of tests they may add to the gliadin antibodies and tTG/EMA might include iron and folate tests (in case of malabsorption). Other tests may also be appropriate depending on your symptoms, past history and family history.
Written by Roslyn (Roz) Ballantyne (RN) for © Gluten Awareness NZ June 2008 to February 2009.
Small bowel biopsy for coeliac disease
If the tTG/EMA tests are positive, the doctors generally recommend confirming coeliac disease by taking a small bowel biopsy. The patient is either given a light general anaesthetic or more commonly in adults is sedated, and a flexible tube (with some instruments inside) is passed down the throat, through the stomach into the small bowel where biopsies (pieces of tissue) are taken. This doesn't take very long and once recovered from sedation/anaesthetic the patient is usually able to go home.
The samples are looked at by a qualified person under a microscope who can see if the villi (small fingerlike projections) on the small bowel surface are showing signs of damage. If they do, a diagnosis of coeliac disease can be made. A repeat small bowel biopsy can be done, to make sure the gluten diet is being effective or if problems persist.
Remember that it is important to not go on a gluten free diet, prior to this test. If coeliac disease is suspected, it is important to have it confirmed as there are long term serious risks if someone with coeliac disease continues to be exposed to gluten. See: Coeliac Disease.
More information: http://www.southerncross.co.nz/index.cfm?FF491968-2357-4A88-A6A2-16830D9F162A#ans3
Gastroscopy
A gastroscopy is where a tube (with some instruments inside) is passed through the oesophagus into the stomach. Gastro meaning "stomach". A gastroscopy is part of the procedure for a small bowel biopsy but to obtain the small bowel biopsy the tube is passed through the stomach into the small bowel. A gastroscopy may be used to look at and take biopsies of the oesophagus and stomach, looking for damage done by gastro-oesophageal reflux, signs of allergies or other abnormalities. See: http://encyclopedia.thefreedictionary.com/gastroscopy for more details.
Genetic predisposition testing
The genes HLA DQ2 or DQ8 are associated with most cases of Coeliac Disease. If you do not have one of these genes, then it is very unlikely that you will have or develop Coeliac Disease. Testing for these genes in some areas of New Zealand may be limited. If you have a close relative who has Coeliac Disease, your risk of having Coeliac Disease is increased but not everyone with the genes HLA DQ2 or DQ8 will develop Coeliac Disease.
Skin allergy testing
Skin allergy testing is useful to determine sensitisation to a food or other allergen. It will only show IgE mediated or immediate immune responses. If a particular test is positive it needs to be put into clinical context i.e. is there a reaction to this substance. For this reason it may be useful to help identify foods etc that are causing symptoms along with a food dairy. A positive reaction does not mean that the food will cause symptoms and need to be avoided. It may also be used to find out if an allergy is likely to have been outgrown.
Before having skin allergy testing, the patient should have not taken any antihistamines for at least three days. The inside of the forearm is the most commonly used site, although in infants their back is often used. Skin allergy testing is done by dropping a small amount of an allergen onto the skin. The skin is then pricked very slightly through the allergen. A negative control and a positive control are also used to gauge how accurate the test is. The negative control should have no wheal and the positive control a wheal. The test is read after a certain amount of time, by measuring the size of the wheals. If the positive control produces no wheal the test is invalid possibly because of antihistamines.
Most laboratories will do skin allergy testing free of charge on referral from a doctor. 30 minutes should be allowed and an appointment is usually required. Some laboratories have a small range of substances they test against. If the patient has had a possible severe reaction (anaphylaxis) the skin allergy tests need to be done at a laboratory with a doctor on the premises. Most allergy specialists also can do skin allergy testing at the time of consultation and in some cases there may be an extra charge for this.
RAST/EAST allergy blood testing
RAST or EAST testing looks at the IgE antibodies in the blood to certain allergens. RAST can be particularly useful when antihistamines can"t be stopped and/or skin testing isn"t practical due to access or skin disease. False positives are possible and this testing will not pick up IgG mediated allergies. As with other testing methods, diagnosis is a combination of test results, history, and dietary elimination and rechallenge. (Sometimes for safety reasons challenge should be done under medical supervision.)
More information: http://www.allergy.org.nz/about+allergies/food+allergy/food+allergy+testing.html
Dietary elimination and challenge
Invitation sent to www.allergyclinic.co.nz to contribute this information 14/02/2009.
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