Indications for Testing
Children and Adolescents
Unexplained gastroenterologic symptoms, poor growth, delayed puberty, iron-deficiency anemia, and abnormal liver testing in children or adolescents warrant testing for CD. Children and adolescents with a specific risk factor for CD should be tested as well, even if they are asymptomatic. Risk factors include autoimmune disorders (type 1 diabetes mellitus, autoimmune thyroiditis, autoimmune liver disease), syndromes associated with CD (Down, Turner, or Williams syndromes), selective IgA deficiency, and first-degree relatives with CD.
Adults
Unexplained gastrointestinal symptoms, unexplained iron deficiency, dermatitis herpetiformis, recurrent aphthous stomatitis, early-onset osteoporosis, delayed puberty/unexplained short stature, or alopecia areata prompt CD testing in adults. Adults with a risk factor for CD should also be tested, even if asymptomatic. Risk factors in adults include family history of CD, syndromes associated with CD (Down syndrome, Turner syndrome), autoimmune disease associated with CD (eg, type 1 diabetes mellitus, thyroid disease, inflammatory bowel disease [IBD]), or selective IgA deficiency.
Criteria for Diagnosis
The European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) has suggested the following criteria for the diagnosis of CD:
- Positive tTG IgA or endomysial antibody (EMA) IgA serologic test, plus biopsy consistent with CD, or
- HLA-DQ2 or HLA-DQ8 positivity in the presence of CD symptoms and high levels of CD-specific antibodies (10 times the upper limit of normal)
The patient should be on a gluten-containing diet when undergoing biopsy or any other CD test. For duodenal biopsy, the gold standard for diagnosis, five or more samples are preferred to increase probability, one or more from the bulb and four or more from the second and third parts of the duodenum. Intestinal damage is assessed using the modified Marsh classification of histologic findings in CD or the simplified system classification.
The American College of Gastroenterology, the World Gastroenterology Association, and the American Gastroesophageal Association have issued similar criteria for CD diagnosis.
Laboratory Testing
Diagnosis
IgA Deficiency Testing
Serum IgA level by nephelometry is the recommended initial test to determine IgA levels before antibody testing. If the patient is IgA deficient, all serologic testing should be performed using IgG tests to prevent false-negative antibody results.
Infants may present with transient, suboptimal levels of IgA and/or IgG that may not be related to immune deficiency.
Antibody Testing Based on IgA Level
Undetectable levels of IgA are typically reported as <7 mg/dL.
- If the patient is not IgA deficient (ie, level is within age-matched range), order tTG IgA, the preferred test for CD.
- If the IgA level is ≥7.0 mg/dL but below the age-matched range, consider a CD dual-antigen screen with reflex, which tests for both IgA and IgG.
- If the IgA level is <7.0 mg/dL, order tTG IgG and deamidated gliadin peptide (DGP) IgG tests.
IgA deficiency may be accompanied by other immunoglobulin deficiencies. Consider evaluating the patient for immune deficiency if IgA levels are below the limit of detection.
See the Antibody Test Results Interpretation table below for details about interpretation of the following specific antibody tests.
Tissue Transglutaminase Antibodies
The tTG IgA test is the recommended single screening test for IgA-competent individuals with possible CD, particularly in patients older than 2 years. The higher the titer, the greater the likelihood that the result is a true positive. Combining several tests, rather than using tTG IgA alone for CD diagnosis, may slightly increase sensitivity but reduces specificity, so this combined testing approach is not recommended for those at low risk for CD. To rule out transient seropositivity, patients with low antibody titers but normal small-intestine mucosa should have serologic tests repeated in 6 months while continuing to consume gluten. In patients with IgA deficiency, tTG IgG testing is recommended (in conjunction with DGP IgG testing).
Endomysial and Deamidated Gliadin Peptide Antibodies
EMA testing, which is highly sensitive for CD, may help differentiate between false-positive and true-positive tTG results. However, EMA testing is expensive and relies on observer expertise.
The tTG IgA test along with the DGP IgA and IgG tests should be considered for screening in children younger than 2 years.
Antibody Test Results Interpretation
| Test |
Result |
Interpretation and/or Next Step |
|---|
| tTG IgA |
High positive (≥41 U/mL) |
CD is likely; consider HLA genotypinga or biopsy |
| Weak-moderate (4-40 U/mL) |
Order EMA IgA by IFA, DGP IgA, and HLA genotypinga |
| Negative (≤3 U/mL) |
CD is unlikely; exclude history of gluten-free diet or immunosuppressive drug, which can cause false-negative results
Consider HLA genotypinga (in light of age and associated diseases)
|
| EMA and/or DGP |
Negative in presence of HLA positivitya |
Perform biopsy |
| Positive in presence of HLA negativitya |
Likely false-negative HLA genotypinga test; consider biopsy to confirm or rule out CD |
| Positive in presence of HLA positivity |
CD confirmed |
| Negative in presence of HLA negativitya |
CD ruled out; any positive tTG test preceding this result was likely false positive |
| CD dual-antigen screen with reflex |
Normal |
CD unlikely |
| Positive or equivocal |
Consider HLA genotypinga |
| tTG IgG and DGP IgG |
Normal |
CD unlikely |
| Positive or equivocal |
Consider HLA genotypinga |
|
aSee HLA Genotyping section below.
IFA, indirect fluorescent antibody
|
HLA Genotyping
HLA-DQ2 is present in approximately 95% of patients with CD, but its presence does not confirm CD because it is found in 20-30% of the general population. HLA-DQ8 is present in approximately 5% of individuals with CD. Although the presence of these genes cannot confirm CD, their absence essentially excludes CD.
HLA genotyping is not necessary for routine laboratory evaluation of CD due to its low positive predictive value, but testing may be indicated in patients at risk for CD, individuals who are repeatedly seropositive but biopsy negative, and patients avoiding biopsy. Biopsy is not needed if tTG IgA results are >10 times the manufacturer’s cutoff and are confirmed by EMA testing in a different blood sample, and HLA testing is positive.
Prognosis
Antiactin (F-Actin) IgA
Antiactin (F-actin) IgA testing by enzyme-linked immunosorbent assay (ELISA) should be performed in biopsy-confirmed cases of CD and can provide information about prognosis. Levels correlate with severity of mucosal damage: The presence of antiactin antibodies may indicate intestinal villus atrophy and a more severe form of disease. Although the F-actin test result may indicate moderate to severe disease, the test lacks specificity.
Screening
There is insufficient evidence to recommend screening for CD in asymptomatic people. Serologic screening for CD is recommended for specific at-risk groups, including first-degree relatives of patients with CD and individuals who have the following :
For asymptomatic children with the above risk factors, begin screening after 2 years of age and when the child has been consuming wheat for at least 1 year, or sooner if CD signs and symptoms manifest.
Monitoring
Monitoring should be performed to assess therapeutic response to change in diet and patient compliance with diet. Monitoring tests include the same assays recommended for diagnosis. tTG, DGP, or EMA assays can be used, depending on previous results, to monitor adherence to a gluten-free diet. In cases of IgA deficiency, IgG testing should be used.
Celiac serologic testing, particularly tTG IgA and DGP IgA, is recommended every 3-6 months after initial diagnosis until abnormal baseline results have normalized or until patient is clinically stabilized, then every 1-2 years. If antibody levels remain elevated after more than 12 months on a gluten-free diet, consider repeating biopsy. A decline in antibody levels, including F-actin IgA, may correlate with normalization of the intestinal villi.
