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How to test for Celiac Disease?

The only way you can get a definite YES or a NO for Celiac Disease (CD) is by doing intestinal biopsy. As this is an invasive and expensive procedure, many prefer measuring serum antibodies as an initial screening process. When someone decides to test for antibodies against gluten it is necessary to keep in mind:

a) that the gluten protein is fairly complex and thus all antibodies need to be tested

b) that the blood test is not a substitute for the biopsy.

Whichever assessment method one decides to use it is important to know that:

For CD, early diagnosis means early intervention with treatment and prevention of long-term complications, including the development of severe and irreversible phenotypes and of other autoimmune disorders.” (Ventura A et al., 2010)

 

Intestinal biopsy is the golden standard for diagnosing Celiac Disease.

 

An individual is classified as celiac when a biopsy of the duodenal mucosa is taken which detects:

a) a reduction or disappearance of intestinal villi &

b) intraepithelial lymphocytes (IELs) higher than 25/100 enterocytes (Sapone A. et al., 2012).

Individuals presenting with significant villous atrophy are classified as CD March stage III, whereas normal villi but increased number of intraepithelial lymphocytes are classified as Marsh I or II (Hill ID et al., 2005). Marsh type II may also suffer from CD but positive serological tests is needed to strengthen the diagnosis (Hill ID et al., 2005). When only elevated IELs are observed but no damage of the intestinal lining, it is difficult to diagnose CD (Kakar eta l., 200). In literature this state is usually referred to as latent CD (Dewar et al., 2005) and further testing is required.

 

Can elevated IELs be due to a different cause other than Celiac Disease?

The presence of IELs can be due to gastrointestinal inflammation caused by H. pylori (Memeo et al., 2005) or tropical sprue (Ross et al., 1981). Unexplained neurological or psychiatric disorders such as autism, schizophrenia, and cerebellar ataxia (Cascella N et al., 2009, Burk K et al., 2009, Genuis S and Bouchard T, 2010) are also linked with elevated IELs and no mucosal damage.

 

Can a blood test confirm Celiac Disease?

No. However, a lot of the time serum antibody testing is used in the screening process. The ones necessary are: anti-DGP IgG & anti-tTG IgA

 

Antibodies for the diagnosis of Celiac Disease

Antibodies

Accurate

Not affected by IgA deficiency

Not prone to interpretation

Cheap

Appropriate for children <2 years old

AGA IgA

AGA IgG

EMA IgA

tTG IgA

DGP IgG

Anti-Actin IgA

 

 

classic Anti-gliadin (AGA) antibody IgA

Pros:

1. relatively cheap

Cons:

1. found in healthy individuals (Bizzaro N et al., 2012)

2. May fluctuate within the first 2 years of age (Simell et al., 2007)

3. relatively insensitive (Fasano A, 2013)

 

AGA-IgG

Pros:

1. useful for pediatric patients with CD who test negative for anti-tTG (Carlsson A et al. 2001, Lagerqvist C et al., 2008).

2. useful in patients with IgA deficiency (Villalta D et al., 2007).

3. reasonably cheap

3. Same results where obtained with the DGP IgG test (Liu E et al., 2007, Agardh D 2007, Basso D et al., 2009, Naiyer A et al., 2009).

4. Remains constant the first 2 years of age (Simell et al., 2007)

Cons:

1. relatively insensitive (Fasano A, 2013)

 

EmA (Endomysial Antibodies – antigliadin) IgA (unless IgG requested)

Pros:

1. It is equally specific with the anti-tTG antibodies, meaning it recognizes the same antigens (Hill 2005)

Cons:

1. It is prone to subjective interpretation

2. It is less sensitive than the anti-tTG (Biagi F et al., 2001, Baudon J et al., 2004, Lock et al., 2004, Kaukinen K et al., 2007).

3. Not accurate in patients with selective IgA deficiency.

4. May fluctuate within the first 2 years of age (Simell et al., 2007)

5 *The IgG version has inferior sensitivity (Fasano A, 2013)

 

anti-tTG (antihuman tissue transglutaminase) IgA (unless IgG requested)

Pros:

1. As it is quantitative, automated and not prone to subjective interpretation

2. high diagnostic sensitivity (95%) specificity (97%) (Tozzoli et al., 2010)

Cons:

1. Anti-tTG IgA is not sensitive enough to be used alone and the addition of the anti-DGP IgG test would increase the accuracy for CD especially in children (Niveloni S et al., 2007, Villalta D et al., 2007, Volta U et al., 2010, Tonutti E et al., 2009, Villalta et al., 2010, Maglio M et al., 2010)

2. May fluctuate within the first 2 years of age (Simell et al., 2007)

3 *The IgG version has inferior sensitivity (Fasano A, 2013)

 

DGP antibodies IgG (deamidated gliadin peptide)

Pros:

1. antibodies comparable sensitivity and specificity to anti-tTG and EMA (Sugai E et al., 2006)

2. Remains constant the first 2 years of age (Simell et al., 2007)

3. DGP IgG test positive in 80% of cases of CD patients with IgA deficiency as compared to 40% for AGA IgG ( Villalta et al., 2010)

 

ANTI-ACTIN IgA

Pros: can evaluate the severity as it is related to the severity of intestinal damage (Granito A et al., 2004, Carroccio A et al., 2005)

Cons: limited usefulness for diagnosis

 

In monitoring of patients on a gluten-free diet, positivity with a low titer of anti-DGP antibodies suggests that the diet should be reassessed, even if the anti-tTG test is negative” (Tursi et al., 2006)

 

Interpretation of serological and biopsy test results

Biopsy

+

Serology

+

CD

Absence of CD and possible false-positive blood test. A negative genetic test can strengthen the negative diagnosis.

This result is treated as CD. However, inflammation in the lining can be due to other causes, including intolerances to other foods.

No CD. However, in the presence of other autoimmune conditions or genetic predisposition, future monitoring may be appropriate.

 

Which other blood biomarkers are available?

While the tests above are the ones most commonly done there is evidence that more thorough testing may be needed for those with negative results and positive symptoms. A complete antibody screening should include: Alpha gliadin, Omega gliadin, Gamma gliadin, Deamidated gliadin, TG2, TG3, TG6.

 

Deamidation is an acid or enzymatic treatment used by the food processing industry to make wheat, water-soluble so it mixes with other foods. It has been shown to cause severe immune responses to people (Leduc V et al., 2003).

Gliadin is broken down to alpha, omega and gamma fractions. If a lab tests only for alpha gliadin antibodies the results may be misleading (Quartesn H et al. 2001).

Elevated antibodies of TG2 indicated a reaction against the intestinal track (Thomas H et al., 2011). Transglutaminase 3 (TG3) is found in the skin. An autoimmune reaction to skin may lead to skin disorder known as dermatitis herpetidormis, which presents as itchy red blisters found usually in the knees, elbows, buttocks but can appear anywhere on the body (Stamnaes I et al., 2010). Elevated antibodies to transglutaminase 6 indicate an immune response against the nervous system (Alessio et al., 2012).