Celiac Disease and Non-Celiac Gluten Sensitivity
A blood test for immunoglobulin A (IgA) type autoimmune tissue transglutaminase antibodies is usually the first diagnostic step for celiac disease in most patients. Another test, IgA endomysial antibodies, may be used to confirm positive results. Deamidated gliadin peptide antibodies are tested for when serum IgA is low, a common occurrence in celiac disease (Ferri 2015; Rubio-Tapia 2013). Elevated antigliadin immunoglobulin G (IgG) antibody levels may also present in people with celiac disease who have recently consumed gluten. However, elevated IgG levels are not specific for celiac disease, and healthy people may sometimes have elevated IgG levels. Combined screening with IgG and IgA tests can be helpful in some cases, especially in people with IgA deficiency, which is thought to occur in about 2‒3% of individuals with celiac disease (ACDA 2015b).
A convenient screening panel, the Celiac Disease Antibody Screen, tests for immunoglobulin A antibodies to tissue transglutaminase, the most important blood test for celiac disease; serum immunoglobulin A levels, which can be low in celiac disease; and deamidated gliadin immunoglobulin A (Rubio-Tapia 2013).
Blood tests alone are often not considered adequate to confirm a diagnosis of celiac disease. The gold standard for a celiac diagnosis is a biopsy of the small intestine demonstrating flattened villi (Guandalini 2014; Gujral 2012; Rubio-Tapia 2013).
Genetic testing for HLA DQ2 and HLA DQ8 may be performed for three reasons: negative tests rule out almost all cases of celiac disease, including those already on a gluten-free diet; negative tests may help clarify the picture when the result of other testing is unclear; and these tests are used to screen close relatives of patients for genetic risk of celiac disease (those who are positive go on to receive conventional testing as listed previously) (Ferri 2015; Kelly 2014; Lidums 2015).
A simple “four-out-of-five” guideline has been proposed for the diagnosis of celiac disease, which would require that a minimum of four out of the five criteria below be met. Current practice guidelines, however, rely on more complex diagnostic algorithms. Generally, a biopsy demonstrating villous atrophy is still considered the “gold standard” for celiac diagnosis (Husby 2012; Rubio-Tapia 2013; Guandalini 2014; Ludvigsson 2014; Sapone 2012).
Four-Out-Of-Five Diagnosis Guideline (Sapone 2012)
- Typical symptoms of celiac disease (See “Signs and Symptoms”).
- Serum celiac disease immunoglobulin A antibodies are strongly positive.
- HLA DQ2 and/or HLA DQ8 genes are present.
- Characteristic changes, known as celiac enteropathy, are evident on small intestine biopsy.
- Positive clinical response to a gluten-free diet.
Distinguishing Celiac Disease from Irritable Bowel Syndrome
The misdiagnosis of celiac disease as irritable bowel syndrome (IBS) deserves special mention. Individuals diagnosed with IBS are considered to be at four- to seven-fold increased risk of celiac disease compared with the general population (Cristofori 2014; Sanders 2001). However, proper diagnosis of IBS necessarily includes ruling out conditions such as celiac disease (Moleski 2013).
Typical gastrointestinal presentation of celiac disease may closely mimic the symptoms of IBS, including recurrent abdominal discomfort, bloating, constipation, and diarrhea (Lidums 2015; Verdu 2009). Patients who have received a diagnosis of IBS should confirm that celiac disease was adequately tested for and ruled out (Rodrigo 2013; Ford 2009; Zwolińska-Wcisło 2009; Spiegel 2004; Sanders 2001). More information on IBS can be found in Life Extension’s Irritable Bowel Syndrome protocol.
Non-celiac Gluten Sensitivity
While there are currently no universally recognized laboratory tests or biomarkers for non-celiac gluten sensitivity, wheat allergy and celiac disease must be ruled out in order to make a non-celiac gluten sensitivity diagnosis (Czaja-Bulsa 2014; Sapone 2012). The best available procedure to confirm non-celiac gluten sensitivity is a double-blind, placebo-controlled gluten challenge that demonstrates that gluten-related symptoms are relieved by a gluten-free diet (Volta 2013; Sapone 2012).