Anti-transglutaminase IgA ELISA: clinical potential and drawbacks in celiac disease diagnosis

BACKGROUND: Since the identification of tissue transglutaminase (tTG) as the antigen for the anti-endomysial antibodies (EMA), several antigen-specific immunoassays have been reported for celiac disease (CD) screening. A first objective was to evaluate the suitability for CD screening of three different IgA tTG ELISAs, two of them based on guinea pig liver tTG (gp-tTG) (an in-house ELISA with a partially purified extract and a commercial ELISA with purified gp-tTG antigen) and a third recombinant human tTG (rh-tTG) ELISA. The results are compared with EMA and with the final clinical diagnosis. A second objective was to analyze antibody reactivities in those patients with anti-tTG and EMA discrepancies. METHODS: ELISA and EMA tests were used to measure IgA anti-tTG levels in sera from 259 patients (107 had CD and 72 had Type I diabetes mellitus). RESULTS: The purified gp-tTG ELISA was highly sensitive (97.7%) and specific (98.8%) in the detection of CD, almost equaling EMA. Rh-tTG ELISA did not improved the sensitivity of EMA, but its specificity was slightly superior. Immunoblot analysis with partially purified gp-tTG extract, the antigen most frequently used for anti-tTG detection, showed that the majority of false positives were due to IgA reactivities to contaminant proteins present in the liver antigenic extract. This low specificity was particularly problematic in diabetics. CONCLUSION: Purified tTG ELISAs, either with purified guinea pig liver or recombinant human antigens, can be used as quantitative and observer-independent alternatives to the traditional and time-consuming EMA in the screening of CD.     

Guinea pig transglutaminase immunolinked assay does not predict coeliac disease in patients with chronic liver disease

BACKGROUND: It has been suggested that serological screening for coeliac disease (CD) should be performed in patients with chronic unexplained hypertransaminasaemia. AIMS: To evaluate the specificity for CD diagnosis of serum IgA antitissue transglutaminase (tTG) determination in consecutive patients with chronic hypertransaminasaemia using the most widely utilised ELISA based on tTG from guinea pig as the antigen. PATIENTS AND METHODS: We studied 98 patients with chronic hypertransaminasaemia, evaluated for the first time in a hepatology clinic. Serum anti-tTG and antiendomysial (EmA) assays were performed. Patients positive for EmA and/or anti-tTG were proposed for intestinal biopsy. Finally, all sera were reassayed for anti-tTG using an ELISA based on human recombinant tTG as the antigen. RESULTS: A total of 94/98 hypertransaminasaemic patients were positive for hepatitis virus markers, with 82/98 (83%) positive for anti-hepatitis C virus. Liver histology showed that most patients had mild or moderate chronic hepatitis while severe fibrosis or overt liver cirrhosis was found in 20/98. CD screening showed that 15/98 (16%) hypertransaminasaemic subjects had anti-tTG values in the same range as CD patients; however, IgA EmA were positive in only 2/98 (2%). Distal duodenal biopsy, performed in nine patients, showed subtotal villous atrophy in the two EmA+/anti-tTG+ patients but was normal in 7/7 EmA-/anti-tTG+ subjects. The presence of anti-tTG+ values in EmA- patients was unrelated to particular gastrointestinal symptoms, other associated diseases, severity of liver histology, or distribution of viral hepatitis markers. There was a significantly higher frequency of positive serum autoantibodies (antinuclear, antimitochondrial, antismooth muscle, and anti-liver-kidney microsomal antibodies) in anti-tTG+/EmA- patients than in the other subjects (9/13 v 10/83; p<0.003). Also, a correlation was found between serum gamma globulin and anti-tTG values (p<0.01). When sera were tested with the ELISA based on human tTG as the antigen, no false positive results were observed: only the two EmA+ patients with atrophy of the intestinal mucosa were positive for anti-tTG while all others were negative, including those false positive in the ELISA based on guinea pig tTG as the antigen. CONCLUSIONS: In patients with elevated transaminases and chronic liver disease there was a high frequency of false positive anti-tTG results using the ELISA based on tTG from guinea pig as the antigen. Indeed, the presence of anti-tTG did not correlate with the presence of EmA or CD. These false positives depend on the presence of hepatic proteins in the commercial tTG obtained from guinea pig liver and disappear when human tTG is used as the antigen in the ELISA system. We suggest that the commonly used tTG ELISA based on guinea pig antigen should not be used as a screening tool for CD in patients with chronic liver disease.     

Comparison of a tissue transglutaminase ELISA with the endomysium antibody test in the diagnosis of gluten-sensitive enteropathy

BACKGROUND: Tissue transglutaminase (tTG) has recently been found to be the major if not the only autoantigen of gluten-sensitive enteropathy (GSE). OBJECTIVES: To further determine the significance of this finding for diagnostic (screening) and follow-up purposes, we performed tTG-based ELISAs, and compared the results to the endomysium antibody test (EMA). PATIENTS: We examined 120 serum samples from patients with celiac disease (CD) including 72 on a gluten-free diet (GFD) and eleven on a gluten challenge, 47 with dermatitis herpetiformis (DH) including 16 on a GFD and one on a gluten challenge, 96 with non-CD gastrointestinal diseases, and 117 with others; i.e. 380 serum samples altogether. Follow-up sera from 13 patients were included. METHODS: Results of an ELISA with guinea pig liver tTG were compared with the EMA test using monkey esophagus. Inhibition of endomysial staining was performed with sera positive on the EMA test but negative with the guinea pig tTG ELISA. RESULTS: The specificity and sensitivity of the tTG ELISA are high (98.6% and 92.5%). The serum IgA antibody titers against tTG decrease after introduction of a GFD. In one case, endomysial staining could not be inhibited. CONCLUSIONS: Our results show that the guinea pig tTG ELISA is suitable for use as a simple diagnostic screening and follow-up method for GSE. Further studies are necessary to identify possible additional minor antigens in GSE.     

Screening for celiac disease in Down＇s syndrome patients revealed cases of subtotal villous atrophy without typical for celiac disease HLA-DQ and tissue transglutaminase antibodies

AIM: To investigate the prevalence of celiac disease (CD) as well as CD marker antibodies and susceptibility HLA-DQ haplotypes in 134 karyotyped Down's syndrome (DS) patients. METHODS: Immunoglobulin A (IgA) and G (IgG) type anti-gliadin antibodies (AGA), IgA type anti-tissue transglutaminase (tTG) antibodies (anti-tTG) with antigen of guinea pig and human source were determined by enzyme-linked immunosorbent assay and endomysium antibodies (EMA) by indirect immunofluoresence test. HLA-DQA1*0501/DQB1*0201 (DQ2) was revealed by polymerase chain reaction. Celiac disease was diagnosed by revised ESPGHAN criteria. RESULTS: 41% of DS patients had AGA, 6.0% IgA anti-tTG with guinea pig antigen, and 3.0 % IgA EMA (all positive for anti-tTG with human tTG). Subtotal villous atrophy was found in 5 out of 9 DS patients who had agreed to small bowel biopsy. One of them had DQA1*0501/DQB1*0201 and anti-tTG and EMA i.e. typical for CD markers (this case also fulfilled the ESPGHAN diagnostic criteria), but other four lacked these markers. Three non-biopsied DS patients had also most probably CD because DQA1*0501/DQB1*0201 and IgA anti-tTG (EMA) were detected. Thus, the prevalence of CD among our DS patients population is 3.0 % (95 % of confidence interval [CI]: 0.1-5.9 %). CONCLUSION: We confirm the increased frequency of CD among DS patients. In addition, we have revealed a subgroup of patients with subtotal villous atrophy but without characteristic for CD immunological and genetic markers. Whether these cases represent CD (with atypical immunopathogenesis) or some other immune enteropathy, requires further investigations.     

Autoantibodies to tissue transglutaminase as predictors of celiac disease

Background & Aims: Immunoglobulin A (IgA) autoantibodies to endomysium (EMA) are highly specific and sensitive markers for celiac disease. Recently, we identified tissue transglutaminase (tTG) as the major if not sole endomysial autoantigen. Methods: An enzyme-linked immunosorbent assay (ELISA) was established to measure IgA anti-tTG titers in serum samples from 106 celiac patients with partial or subtotal villous atrophy, 43 celiac patients on a gluten-free diet, and 114 diseased and healthy controls. Results were correlated with clinical and histological data and with EMA titers. Results: In patients with biopsy-proven celiac disease consuming a normal, gluten-containing diet, 98.1% of the serum samples had elevated IgA titers against tTG, whereas 94.7% of the control sera were negative. IgA anti-tTG correlated positively with semiquantitative IgA EMA titers (r = 0.862; P < 0.0001). Conclusions: An ELISA based on tTG allows diagnosis of celiac disease with a high sensitivity and specificity. IgA anti-tTG and IgA EMA show an excellent correlation, further confirming the enzyme as the celiac disease autoantigen. Because the assay is quantitative, not subjected to interobserver variation, and easy to perform, it will be a useful tool for population screening of a hitherto underdiagnosed disease.GASTROENTEROLOGY 1998;115:1317-1321     

Autoantibodies to tissue transglutaminase in Sjögren's syndrome and related rheumatic diseases

OBJECTIVE: Sj?gren's syndrome (SS) has been reported in up to 15% of patients with biopsy proven celiac disease (CD). The diagnosis of CD in the setting of SS and other systemic rheumatic diseases can be difficult because they are often associated with a number of gastrointestinal symptoms and diseases. Although the diagnosis of CD is often confirmed by a small bowel biopsy, marker autoantibodies directed against the endomysium of transitional epithelium (EMA) and tissue transglutaminase (tTG) are highly correlated with biopsy-proven disease and serve as a valuable screening test. We used an IgA-anti-tissue transglutaminase antibody (anti-tTG) ELISA to assess the prevalence of anti-tTG in an unselected cohort of patients with SS and other systemic rheumatic diseases. METHODS: Sera from 50 patients with SS, 50 with systemic lupus erythematosus (SLE), 50 with rheumatoid arthritis (RA), 30 with systemic sclerosis (SSc), and 50 healthy controls were tested for autoantibodies to tTG. A comparison group of 40 sera from patients with biopsy-confirmed CD was also included. IgA anti-tTG was measured by a commercially available ELISA kit (Inova, San Diego, CA) that employs purified tTG. RESULTS: Six of the 50 (12%) IgA sufficient SS patients had anti-tTG compared to 2 (4%) normal sera, 3 (6%) SLE, 2 (7%) SSc, and 1 (2%) RA. By comparison, in the CD cohort, 33 (83%) had anti-tTG. Five of 6 SS patients with anti-tTG had symptoms, signs, or small bowel biopsy findings consistent with a diagnosis of CD. IgA anti-tTG and EMA were accompanied by other IgA autoantibodies in SS sera. CONCLUSION: Anti-tTG ELISA is a reliable method to indicate a coexisting diagnosis of CD in patients with SS. Interestingly, the frequency of false positive tTG tests in any of the systemic rheumatic diseases is not significantly greater than in controls. Further, our study shows that anti-tTG is more prevalent in SS than in other systemic rheumatic diseases. The tTG ELISA may be used as a screening test to identify patients with SS who are at risk and require further evaluation for the presence of CD.     

High rate of positive anti-tissue transglutaminase antibodies in chronic liver disease. Role of liver decompensation and of the antigen source

BACKGROUND: Since the recognition of tissue transglutaminase (tTG) as the target antigen of anti-endomysium antibodies, several ELISA assays using either guinea pig or human recombinant tTG have been developed. The aim of the study was to compare the behaviour of anti-tTG and anti-endomysium antibodies assays in coeliacs and in patients with chronic liver disease. METHODS: 34 patients (24 women, 34.9 +/- 12.5 years) with coeliac disease and 41 with chronic liver disease (14 women, 57 +/- 11.2 years), including 19 cirrhotics, were evaluated for anti-endomysium antibodies by indirect immunofluorescence and for anti-tTG IgA antibodies by ELISA, using guinea pig liver or human recombinant transglutaminase. RESULTS: The prevalences of anti-tTG and anti-endomysium antibodies were 100% in patients with coeliac disease at diagnosis, 75% and 64.3% in patients on a gluten-free diet. All liver disease patients were negative for anti-endomysium antibodies, while 11 (26.8%) were positive for anti-tTG. All these patients had liver cirrhosis and represented 57.9% of all cirrhotics. The presence of anti-tTG was associated with higher Child-Pugh scores. The use of human transglutaminase determined a reduction in the rate of positive results; however, the rate of positive anti-tTG was still 17.1% in all liver disease patients and 31.6% in cirrhotics. CONCLUSIONS: Our data confirm that anti-tTG have a similar sensitivity compared with anti-endomysium antibodies assay in coeliacs. However, a high prevalence of positive anti-tTG results is observed in cirrhotic patients, even when human recombinant tTG is used. The high prevalence of positive results among cirrhotic patients is associated with more advanced liver disease.     

High Rate of Positive Anti-Tissue Transglutaminase Antibodies in Chronic Liver Disease

Background: Since the recognition of tissue transglutaminase (tTG) as the target antigen of anti-endomysium antibodies, several ELISA assays using either guinea pig or human recombinant tTG have been developed. The aim of the study was to compare the behaviour of anti-tTG and anti-endomysium antibodies assays in coeliacs and in patients with chronic liver disease. Methods: 34 patients (24 women, 34.9 ± 12.5 years) with coeliac disease and 41 with chronic liver disease (14 women, 57 ± 11.2 years), including 19 cirrhotics, were evaluated for anti-endomysium antibodies by indirect immunofluorescence and for anti-tTG IgA antibodies by ELISA, using guinea pig liver or human recombinant transglutaminase. Results: The prevalences of anti-tTG and anti-endomysium antibodies were 100% in patients with coeliac disease at diagnosis, 75% and 64.3% in patients on a gluten-free diet. All liver disease patients were negative for anti-endomysium antibodies, while 11 (26.8%) were positive for anti-tTG. All these patients had liver cirrhosis and represented 57.9% of all cirrhotics. The presence of anti-tTG was associated with higher Child-Pugh scores. The use of human transglutaminase determined a reduction in the rate of positive results; however, the rate of positive anti-tTG was still 17.1% in all liver disease patients and 31.6% in cirrhotics. Conclusions: Our data confirm that anti-tTG have a similar sensitivity compared with anti-endomysium antibodies assay in coeliacs. However, a high prevalence of positive anti-tTG results is observed in cirrhotic patients, even when human recombinant tTG is used. The high prevalence of positive results among cirrhotic patients is associated with more advanced liver disease.     

Predictive value of serological tests in the diagnosis of celiac disease

In the diagnostic work-up of celiac disease (CD) the simpler enzyme-linked immunosorbent assay (ELISA) for the identification of serum anti-transglutaminase (tTG) autoantibodies could substitute the immunofluorescence technique used for the detection of anti-endomysial antibodies (EmA). However, most of the studies on anti-tTG assay have considered pre-selected groups of patients and not consecutive subjects with suspected CD. The aim of this study was to compare the sensitivity, specificity and predictive value of anti-gliadin antibodies (AGA), EmA and two anti-tTG ELISAs, one based on guinea pig (gp)-tTG and the other on human (h)-tTG as antigens, in consecutive patients investigated for suspected CD. The study included 130 consecutive patients (age range 16-84 years), who underwent intestinal biopsy for suspected CD. They presented with one or more of the following symptoms: weight loss, anemia, chronic diarrhea, abdominal pain, dyspepsia, alternating bowel habits and constipation. At the time of admission in the study, an intestinal biopsy was performed and a serum sample was taken for immunoglobulin (Ig) G and IgA AGA, IgA EmA, anti-gp-tTG and anti-h-TG determination. Intestinal histology revealed that 15 patients had partial or total villous atrophy. In these patients the diagnosis of CD was confirmed at subsequent follow-up. The remaining 115 patients included in the study had an intestinal histology characterized by a normal villi/crypts ratio and were considered as controls. Serum EmA, anti-gp-tTG, and anti-h-tTG were positive in all the 15 CD subjects, whereas IgG and IgA AGA were positive in 10/15; in the control group, none were positive for serum EmA, but 11/115 (10%) were positive for anti-gp-tTG and 6/115 (5%) were positive for anti-h-tTG. The sensitivity was 100% for EmA, gp-tTG and h-tTG and 66% for IgA and IgG AGA. The specificity was 100% for EmA, 90% for anti-gp-tTG, 95% for anti-h-tTG, 74% for IgG AGA and 87% for IgA AGA. The negative predictive value was 100% for EmA, anti-h-tTG and anti-gp-tTG, 94% for IgG AGA and 95% for IgA AGA. The positive predictive value was 100% for EmA, 71% for anti-h-tTG (p = 0.03 vs EmA) and 58% for anti-gp-tTG (p = 0.003 vs EmA). Most of the patients who were false positive for anti-tTG had Crohn's disease or chronic liver disease. In conclusion, although both the anti-tTG ELISAs evaluated in the present study showed an optimum sensitivity, their low specificity determined positive predictive values which were significantly lower than those of EmA assay. Besides, the positive predictive value of gp-tTG was too low to warrant submitting a patient to intestinal biopsy for suspected CD.     

Anti-tissue transglutaminase antibodies in inflammatory and degenerative arthropathies

Recent studies identified tissue transglutaminase (tTG) as the antigen eliciting antiendomysial antibodies (EMA) in celiac disease (CD). Anti-tTG antibodies have therefore been proposed as a serological test for CD. Nevertheless, IgA anti-tTG but not EMA have also been found in inflammatory bowel disease patients, suggesting that these antibodies are linked to a tissue lesion rather than to an auto-immune component of CD. To confirm this hypothesis, we evaluated the presence of IgA anti-tTG in patients with inflammatory and degenerative diseases, in whom tissue lesions presented far away from the intestinal mucosa. The study was carried out on the serum and synovial fluid (SF) of 68 patients with rheumatoid arthritis (RA=33), psoriatic arthritis (PsA=26) and osteoarthritis (OA=9). In RA, PsA and OA sera, IgA anti-tTG were positive in 33%, 42% and 11% of patients, respectively. Serum anti-tTG levels were significantly higher in RA (p<0.0001), PsA (p<0.0001) and OA (p<0.02) with respect to healthy controls. SF anti-tTG levels were significantly higher in PsA (p<0.018) than in OA. A good correlation between serum and synovial fluid anti-tTG levels was found in all arthropathies This study suggests that tTG is not the only antigen of EMA and, furthermore, that IgA anti-tTG antibodies represent a general lesion-associated event. Moreover, the significant correlation between serum and synovial fluid anti-tTG levels allow us to hypothesise that these antibodies could be synthesized in the site of arthritic lesions.     

IgA and IgG Tissue Transglutaminase Antibody Prevalence and Clinical Significance in Connective Tissue Diseases, Inflammatory Bowel Disease, and Primary Biliary Cirrhosis

An association between celiac disease (CD) and other autoimmune diseases such as connective tissue diseases (CTD), inflammatory bowel diseases (IBD), and primary biliary cirrhosis (PBC) has been reported in several studies. However, a high rate of false positives in autoantibody testing was noted, especially when tissue transglutaminase (tTG) from guinea pig liver was used. Thus, the real prevalence of CD in CTD, IBD, and PBC is unclear. In a case-control study, 400 patients with CTD, 170 with IBD, 48 with PBC, and 120 healthy subjects were investigated for CD by the analysis of IgA and IgG tTG antibodies using the more specific human recombinant tTG immunoenzymatic assay. Patients and controls with positive findings were further tested for antiendomysial antibodies by indirect immunofluorescence and HLA typing, and those found positive by either of these tests underwent duodenal biopsy to confirm a possible diagnosis of CD. Twelve patients were positive for IgA or IgG tTG antibodies, showing an overall prevalence of 1.9%. Only 1 healthy subject (0.8%) had a low level positive reaction for IgA anti-tTG. Among the 12 patients and the healthy subject, only 2 (1 SLE and 1 ulcerative colitis patient) were subsequently confirmed to be affected with CD by positive EMA, HLA, and small bowel biopsy findings. The highest rate of false positives was found in PBC patients (10.4%). For these reasons, serological screening testing for CD is not recommended in CTD patients or in subjects affected with IBD or PBC, unless there is a relevant clinical suspicion of CD.     

Elevation of IgG antibodies against tissue transglutaminase as a diagnostic tool for coeliac disease in selective IgA deficiency

BACKGROUND: IgA serum autoantibodies against tissue transglutaminase (tTG) have an established diagnostic value in coeliac disease, and high efficacy tests are widely available for their detection. However, serological evaluation of IgA deficient subjects is still difficult. AIMS: To evaluate the diagnostic potential of IgG class anti-tTG autoantibodies measured quantitatively using an enzyme linked immunosorbent assay (ELISA) compared with immunofluorescent detection of coeliac autoantibodies. PATIENTS: We tested serum samples from 325 IgA deficient subjects, including 78 patients with coeliac disease, 73 disease controls, and 174 blood donors. METHODS: IgG antibodies against human recombinant tTG were measured with an ELISA. IgG antiendomysium antibodies (EMA) were assayed by indirect immunofluorescence on human jejunum and appendix sections. RESULTS: The IgG anti-tTG ELISA had a sensitivity of 98.7% and a specificity of 98.6%, and the correlation with IgG EMA titres was high (r(s)=0.91). One coeliac patient, initially negative in all autoantibody tests, displayed both IgG anti-tTG antibodies and IgG EMA during later gluten exposure. IgG anti-tTG antibodies and EMA titres showed significant decreases (p<0.001) in treated patients. The frequency of IgG anti-tTG autoantibody positivity was 9.8% among IgA deficient blood donors and 11 of the 12 positive subjects with known HLA-DQ haplotypes carried DQ2 or DQ8 alleles. CONCLUSIONS: IgG anti-tTG and IgG EMA autoantibody tests are highly efficient in detecting coeliac disease in IgA deficient patients. The high prevalence of coeliac antibodies among symptom free IgA deficient blood donors who also carry coeliac-type HLA-DQ genes indicates that all IgA deficient persons should be evaluated for coeliac disease.     

Antibodies Against Human Tissue Transglutaminase and Endomysium in Diagnosing and Monitoring Coeliac Disease

Background: Coeliac disease (CD) patients often present a variety of uncharacteristic symptoms and therefore sensitive and specific screening tests are needed as an aid in making an accurate diagnosis. A recently developed ELISA, using human recombinant tissue transglutaminase (tTG) as antigen, was evaluated for its significance in the diagnosis of CD. The patient's compliance to a gluten-free diet and the serological reaction during gluten challenge were also monitored. The results were compared with IgA-endomysium antibody (EMA) results. Methods: Sera previously collected from 365 patients (0.4-76 years) with jejunal biopsy on a gluten-containing diet and from 41 patients on a gluten-free diet or challenge were tested for IgA anti-human tTG antibodies (IgA tTG ab) with Celikey ® (Pharmacia Diagnostics). The study population comprised 208 CD patients and 157 controls. The diagnostic performance and cut-off for the assay were estimated with ROC analysis. EMA was analysed by indirect immunofluorescence microscopy on cryostat sections of monkey oesophagus. Results: 200/208 patients with CD had positive IgA tTG ab (median >100 U/ml), while only 1/157 of the control patients were positive (median 1.67 U/ml). The area under the ROC curve was 98.3% and the sensitivity and specificity of the test were 96% and 99% for the study population. Only 4/365 patients (1%) presented discordant IgA tTG ab and EMA results, 2 of them had only IgA tTG ab and 2 only EMA. The IgA tTG ab levels and the EMA titres were closely correlated to the duration of gluten-free diet and gluten challenge, respectively. Conclusion: IgA tTG ab can be used as an accurate observer-independent alternative to EMA in diagnosing or monitoring CD.     

Population screening for coeliac disease in a low prevalence area in Italy

Objective. A screening program was proposed for the village of Carcare (population 5700), located in a region of Italy with an apparently low prevalence of coeliac disease (CD): only 1 patient diagnosed out of 2557 inhabitants. The study group comprised 1002 individuals (568?F, 434?M, age range 13–90 years) recruited from blood donors, secondary school pupils and people referred to the local outpatient facilities for routine blood chemistry. Material and methods. Total IgA, IgA anti-tissue transglutaminase (tTG) (ELISA, recombinant human antigen) and IgA antiendomysium (EMA) (IFI, umbilical cord substrate) antibodies were measured in the serum of all participants. All patients with IgA deficiency were investigated for IgG tTG antibodies, and in the case of disagreement between tTG and EMA, they were typed for HLA DQ2-DQ8 haplotypes. Results. Thirteen subjects were positive and 988 negative for autoantibodies (3/988 had IgA deficiency). One serum sample was positive for tTG antibodies but negative for EMA. Ten out of 13 positive subjects consented to undergo duodenal biopsy, which invariably produced evidence of CD despite the absence of clinical signs/symptoms. A post-diagnostic clinical investigation provided evidence showing mild iron deficiency (4 subjects) and osteoporosis (2 subjects). After counselling, all subjects accepted a gluten-free diet. Conclusions. The prevalence of CD in the study group was 1:100 (1.0%; 95% CI: 0.5–1.8%): this indicates that CD is largely underdiagnosed in Carcare. Our results suggest that the low prevalence of CD observed in some regions is likely to be due to underdiagnosis.     

Antibody testing in Indian children with celiac disease.

BACKGROUND: We prospectively evaluated the usefulness of IgA tissue transglutaminase antibodies (IgA tTG) in the initial diagnosis of celiac disease (CD) and compared its diagnostic potential with that of IgA anti-endomysial antibodies (IgA EMA) and anti-IgA and IgG gliadin antibodies (AGA and AGG, respectively). METHODS: Sera of 23 untreated children fulfilling the revised ESPGHAN criteria for diagnosis of CD (Group I; mean age 10.8 y); 19 disease controls (Group II; mean age 8.5 y) presenting with chronic diarrhea, short stature or both; and 22 healthy children (Group III; mean age 8.8 y) were studied. These were tested in a blinded manner for AGA, AGG, IgA tTG (guinea pig as antigen) and IgA EMA. RESULTS: In Group I, IgA EMA was positive in 19, IgA tTG in 17, AGA in 14 and AGG in 17 patients. In Group II, these tests were positive in 1, 0, 2 and 14 patients, respectively and in Group III, in 0, 0, 0 and 1 child, respectively. Analyzing data from Group I and II, IgA EMA, IgA tTG, AGA and AGG had sensitivity rates of 83%, 74%, 61% and 74%, respectively; the specificity rates were 95%, 100%, 89% and 26%; positive predictive values were 95%, 100%, 88% and 55% and negative predictive values were 82%, 74%, 65% and 45%, respectively. CONCLUSION: IgA tTG is useful for the diagnosis of CD, with sensitivity and specificity rates comparable to those of EMA and this test is well suited for use in tropical countries like India.     

Coeliac disease in Iraqi type 1 diabetic patients

Background and study aimsHigh prevalence rates of coeliac disease (CD) in patients with type 1 diabetes mellitus (T1DM) have been reported. The aim of this study was to evaluate the frequency of silent CD in a sample of Iraqi patients with T1DM.Patients and methodsThis is a cross-sectional study done in Baghdad Teaching Hospital, Baghdad Medical City, Baghdad, Iraq, on 62 patients with T1DM. For all patients, immunoglobulin A (IgA) anti-tissue transglutaminase antibodies (IgA tTG), IgG anti-tissue transglutaminase antibodies (IgG tTG), IgA endomysial antibody (IgA EMA), IgA antigliadin antibodies (IgA AGA) and IgG antigliadin antibodies (IgG AGA) tests were done, with duodenoscopy, and at least four biopsies were taken from the second part of the duodenum.ResultsA total of 27 patients (43.5%) had normal small-intestinal histopathology (Marsh 0), one of them had a positive result for all serological markers used in the study, and another patient was positive for IgA tTG only. Ten patients (16.1%) had Marsh grade I, one of them was positive for IgA tTG, IgG tTG and IgA EMA, another patient was IgA deficient and had positive IgG tTG only and another patient with Marsh I had positive IgA tTG and IgG tTG only. Two patients (3.2%) had Marsh IIIA; three patients (4.8%) had Marsh IIIB histopathology, two of them were positive for all tests and one had positive IgA tTG and IgA EMA only. Two patients (3.2%) had Marsh IIIC histopathological features; they were positive for all serological tests, hence, the frequency of CD was 11.2%.ConclusionThe frequency of silent CD in Iraqi patients with T1DM is not rare, reaching up to 11.2%. Both EMA and tTG antibodies are useful as screening tests.     

Antibodies against human tissue transglutaminase and endomysium in diagnosing and monitoring coeliac disease

BACKGROUND: Coeliac disease (CD) patients often present a variety of uncharacteristic symptoms and therefore sensitive and specific screening tests are needed as an aid in making an accurate diagnosis. A recently developed ELISA, using human recombinant tissue transglutaminase (tTG) as antigen, was evaluated for its significance in the diagnosis of CD. The patient's compliance to a gluten-free diet and the serological reaction during gluten challenge were also monitored. The results were compared with IgA-endomysium antibody (EMA) results. METHODS: Sera previously collected from 365 patients (0.4-76 years) with jejunal biopsy on a gluten-containing diet and from 41 patients on a gluten-free diet or challenge were tested for IgA anti-human tTG antibodies (IgA tTG ab) with Celikey (Pharmacia Diagnostics). The study population comprised 208 CD patients and 157 controls. The diagnostic performance and cut-off for the assay were estimated with ROC analysis. EMA was analysed by indirect immunofluorescence microscopy on cryostat sections of monkey oesophagus. RESULTS: 200/208 patients with CD had positive IgA tTG ab (median >100 U/ml), while only 1/157 of the control patients were positive (median 1.67 U/ml). The area under the ROC curve was 98.3% and the sensitivity and specificity of the test were 96% and 99% for the study population. Only 4/365 patients (1%) presented discordant IgA tTG ab and EMA results, 2 of them had only IgA tTG ab and 2 only EMA. The IgA tTG ab levels and the EMA titres were closely correlated to the duration of gluten-free diet and gluten challenge, respectively. CONCLUSION: IgA tTG ab can be used as an accurate observer-independent alternative to EMA in diagnosing or monitoring CD.     

A reliable screening procedure for coeliac disease in clinical practice

BACKGROUND: The main autoantigen recognized by the sera of patients with coeliac disease (CD) is tissue transglutaminase (tTG). A human-recombinant form of tTG was used to develop an ELISA to measure anti-tTG serum antibodies for the diagnosis of CD. Preliminary retrospective reports suggest that the human tTG-based ELISA could identify coeliac patients missed by the IgA-anti-endomysium antibody test (AEA). Whether the human recombinant tTG ELISA is sufficiently accurate to become the main diagnostic CD tool in everyday clinical practice is unknown. The objective was to determine, in a prospective study, the sensitivity and specificity of an ELISA test based on the use of human tTG compared with AEA, to analyse the discordant cases for HLA DQ2-8 and for clinical and intestinal biopsy characteristics. METHODS: 1106 patients referred to a gastrointestinal outpatient clinic for symptoms attributable to CD, 52 first-degree relatives of CD patients and 200 healthy controls were tested for both anti-human tTG and AEA antibodies. RESULTS: Out of 1158 subjects, 146 were tested positive for anti-tTG antibodies and 140 were biopsy-proven coeliacs. The AEA test identified 126/1158 coeliacs who also tested positive for anti-tTG antibodies. The 14 patients missed by the AEA test carried the typical HLA-DQ for CD; they had normal levels of total serum IgA and had milder pathology than those with both anti-tTG and AEA positivity (P < 0001). CONCLUSIONS: These results prove that human tTG-based ELISA is an excellent diagnostic tool for CD, for mass screening by both the specialist and the general clinic.     

Screening for celiac disease in non-Hodgkin's lymphoma patients: a serum anti-transglutaminase-based approach

Several studies have shown the existence of an association between celiac disease (CD) and non-Hodgkin's lymphoma (NHL). Our aim was to evaluate the usefulness of the serum anti-tissue transglutaminase (anti-tTG) antibody assay in screening for CD in consecutive NHL patients. In all, 80 consecutive patients (median age 61 years) with a new diagnosis of NHL were included. To compare the frequency of CD and of positive results for the anti-tTG assay, we enrolled 500 blood donors. In all patients serum anti-tTG was determined with two different ELISA: one based on tTG from guinea pig (gp-tTG) and the other based on human recombinant t-TG (h-tTG) as the antigens. Serum anti-endomysial antibodies (EmA) were also assayed. Subjects with positive serum EmA and/or anti-tTG underwent intestinal biopsy for histology study, HLA-DQ phenotype determination, and serum anti-gliadin (AGA) assay. Eight of 80 (10%) NHL patients were positive for anti-tTG ELISA—two of these exclusively for anti-gp-tTG and six for anti-h-tTG (7.5%). None of the 80 NHL patients were positive for serum EmA. The frequency of anti-tTG positivity in the blood donor controls was 2/500 (0.4%), significantly lower than that observed in the NHL patients (P < 0.0001). Both these blood donors were found to have CD. Only in one anti-h-tTG-positive NHL patient was there intestinal mucosa atrophy, and follow-up confirmed a CD diagnosis (CD frequency in NHL patients is 1.2%; versus blood donors: P = 0.4). In all the other seven anti-tTG-positive NHL patients a normal intestinal architecture was found, although, inflammatory infiltration of the lamina propria was observed in four patients. No anti-tTG-positive NHL patients, including the subject diagnosed as having CD, had a family history of CD, and all had normal weight and no signs of malabsorption. Anti-tTG false positive results were associated with a higher frequency of serum autoantibody positivity and T-cell type NHL. In conclusion, NHL patients the anti-tTG assay often gives discordant data with the EmA assay, with a high frequency of anti-tTG false positive results for CD diagnosis.     

IgA and IgG tissue transglutaminase antibodies in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) and coeliac disease (CD) are diseases of an autoimmune origin that share the human leukocyte HLA-B8 and HLA-DR3 histocompatibility antigens, yet the co-association of CD with SLE is mainly based on case reports. Thus, the real prevalence of CD in SLE is unclear. The aim of this study was to determine the prevalence of antitissue transglutaminase (anti-tTG) in SLE and the relation between SLE and CD. In this case-control study, 100 patients with SLE, and 120 healthy subjects were studied. Sera from all participants were analysed for the presence of IgA and IgG anti-tTG antibodies using a human recombinant tissue transglutaminase (tTG) immuno-enzymatic assay. Anti-tTG positive patients and controls were further tested for antiendomysial (EMA) antibodies by an indirect immunofluorescence and HLA typing (DQalpha1*0501-DQbeta1*0201 allele determination). Subjects who had EMA or the mentioned allele, underwent duodenal biopsy to confirm a possible diagnosis of CD. Anti-tTG antibodies (IgA or IgG isotypes) were found in three of the 100 SLE patients (overall prevalence of 3%): one had the IgA and two the IgG isotypes. Only 1 of 120 healthy subjects (0.8%) had a low positive reaction for IgA anti-tTG. Only the IgA anti-tTG positive SLE patient was diagnosed as having CD based on a positive IgA-EMA and small bowel biopsy findings. The two IgG anti-tTG positive SLE patients and the IgA anti-tTG positive healthy subject were classified as false positives (EMA negative and HLA DQalpha1*0501-DQbeta1*0201 allele negative). In conclusion, anti-tTG antibodies were found at a low rate in SLE patients and mostly did not indicate the presence of CD. Thus, serological screening for CD is not recommended in SLE, unless a clinical suspicion of CD is present.