1. Introduction

Celiac disease (CD) is an autoimmune inflammatory disorder of the small intestine, triggered by the ingestion of prolamins contained in wheat, barley or rye, in genetically susceptible individuals. The prevalence of “suspected” celiac disease varies from 1 in 87 to 1 in 500 individuals in western countries. The majority of patients are undiagnosed since diagnosed cases of CD have a much lower prevalence being somewhere between 1 in 500 to 1 in 9000 individuals. In high risk populations, the average risk of CD can reach 5-10%.

There is an increased risk of complications such as hematological and gastrointestinal malignancies, osteoporosis/penia and other extraintestinal manifestations, decreased height, malnutrition and nutritional deficiencies, fertility impairment, stillbirth, dismaturity, psychosocial retardation, impairment of quality of life, increased mortality and additional autoimmune conditions, if left untreated. Thus early diagnosis and subsequent adherence to a gluten-free diet is highly recommended. The epidemiology and phenotype of CD are constantly changing. It has been shown that the classic intestinal clinical picture of malnutrition, chronic diarrhea and nutritional deficiencies are disappearing and extraintestinal presentations are emerging. Skin, endocrine, skeletal, hepatic, hematological, thrombophylic, gynecological, fertility, dental and behavioral abnormalities are often described. Nowadays, we are witnessing an epidemiological shift in the disease phenotype toward a more advanced age, and increased prevalence of latent, hyposymptomatic or asymptomatic behavior ^{[1, 2]}. All these changes make the diagnosis of the disease more difficult and the reliance on symptomatology more remote ^[3]. These are some of the reasons why serological screening and diagnosis of CD have achieved prime importance.

2.General or Case-Finding Screening

CD fulfills most of the major criteria for mass screening: it has a high prevalence, sensitive and specific biomarkers are available, it responds to a gluten-free diet, untreated it leads to morbidity/mortality, early detection is problematic and there are latent and early symptomatic stages. Despite this, mass screening for CD, as a public health intervention is controversial and data concerning the cost-effectiveness of case detection are sparse ^{[4, 5]}. The main arguments against screening are: low compliance to a gluten-free diet in screen-detected patients, unacceptably low positive predictive values of current serological tests (given the pretest prevalence of less than 1%), poor understanding of the natural course of CD, conflicting mortality data with regard to undiagnosed CD and the above mentioned lack of data regarding cost-effectiveness. The general consensus is that there are insufficient data to justify mass screening of CD in the general population ^{[4, 5]}.

In contrast, screening targeted to high-prevalence groups may prove to have a favorable cost-benefit ratio, prevent or ameliorate associated autoimmune diseases and decrease complications including the risk of malignancy. Arguments against screening high-prevalence groups include low adherence to a gluten-free diet and the lack of any improvement in quality of life ^[4]. The high-prevalence asymptomatic groups that are recommended for CD screening in children and adults are shown in Table 1.

Table 1. Asymptomatic, high risk groups who should be screened for celiac disease

Download as

PowerPoint Slide

Larger image(png format)

Tables index

Veiw figure

View current table in a new window

View next table

3. Diagnostic Autoantibodies in CD

The specificity and sensitivity of the serological markers is very wide-ranging from 29-100%. No single marker is 100% sensitive and specific. It appears that the combination tests perform better, and are capable of detecting close to 100% of all celiac cases ^{[4, 5, 9, 10, 14, 17, 18, 23, 24, 25, 26]}.

Despite the fact that the market for serological biomarkers is very dynamic and future studies can change the reported performance, looking at Table 1, at the present time, the following conclusions can be drawn: In children, the best single tests are IgA-tTG and EMA and the best combination test is Celicheck (antibodies against neo-epitope of the GDP-tTG complex). However, in adults, the best single tests is IgA-tTG and the best combination tests are IgA-tTG and EMA, and IgG-DGP/IgA-tTG. Our own experience ^{[17, 18, 19]} and that of many others ^{[4, 5, 9, 10, 14, 17, 18, 22, 23, 24, 25, 26]} favors combination tests to screen for CD. The main ELISA kit candidates are anti tTG-IgA and anti-DGP IgG competing with the new Celicheck combination of IgA and IgG antibodies against the neo-epitope of the GDP-tTG complex, thus omitting screening for IgA deficiency ^{[17, 18, 19, 27, 28]}.

Table 2. summarizes the sensitivity and specificity of the current serological biomarkers in CD patients

Download as

PowerPoint Slide

Larger image(png format)

Tables index

Veiw figure

View current table in a new window

View previous table

Formation of the tTG-DGP complex is known to involve epitope spreading from gliadin to tTG ^[28].The antibodies against neo-epitopes of the tTG-DGP complex provide a new screening and diagnostic test in CD. Multiple studies have exhibited diagnostic sensitivities of 95% and specificities of 97% or more, when compared with those of traditional antibody assays ^{[16, 29]}. The neo-epitope tTG/DGP is able to drive the development of 3 different autoantibodies: against DGPs, against tTG and against newly formed epitopes derived from the cross-linkage between the enzyme and the substrate. It was suggested that these neo-epitope directed antibodies appear early during the development of CD, preceding the formation of anti DGP and anti tTG, through a mechanism of epitope spreading, imitating the appearance of autoantibodies in SLE. It is foreseeable that the autoantibodies generated against the neo-epitope complex may represent the best means for screening populations and for diagnosing high-risk groups for identification of the silent or latent patients. In fact, several studies have shown the superiority of screening for CD using the tTG/DGPs complex strategy in the general population ^{[29, 30]} or in groups of at-risk subjects ^{[17, 18, 19, 31, 32, 33]}. Most recently, neo-epitope DGP/tTG autoantibodies were shown to present a new and sensitive serological marker of dermatitis herpetiformis, a disease closely related to CD ^[34].

4. Summary

Since only the tip of the CD iceberg is above the waterline and the much larger portion of the CD iceberg remains undetected underwater, it can be expected that the prevalence of the disease will continue to increase and that the presenting symptoms of the disease will continue to change towards a/hyposymptomatic ones, supporting the need to screen and diagnose the disease. At present, there is insufficient information to demonstrate that screening the general population definitely results in clinical benefit. However, asymptomatic individuals in high-prevalence groups should be screened. Multiple serological tests exist on the market and the most frequently used one is IgA-tTG. This is not sensitive enough to be used alone, and is better combined with other tests. Several combinations have been studied but not accurately compared with each other. The most frequently used is anti IgG-DGP and IgA-tTG, however, the new generation anti neo-epitope DGP+tTG IgG+IgA is increasingly being used.

References

[1]	Lerner A. Factors affecting the clinical presentation and time diagnosis of celiac disease: The Jerusalem and the West Bank-Gaza experience. Isr J Med Sci. 1994; 11: 294-295.
	In article
[2]	Lerner A, Agmon-Levin N, Shapira Y, Gilburd B, Reuter S, Lavi I, Shoenfeld Y. The thrombophilic network of autoantibodies in celiac disease. BMC Med. 2013; 11: 89.
	In article		CrossRef
[3]	Katz KD, Rashtak S, Lahr BD et al. Screening for celiac disease in a North American population: sequential serology and gastrointestinal symptoms. Amer J Gastroentrol 2011; 106: 1333-1339.
	In article		CrossRef
[4]	Aggarwal S, Lebwohl B, Green PH. Screening for celiac disease in average-risk and high-risk populations. Therap Adv Gastroenterol. 2012; 5: 37-47.
	In article		CrossRef
[5]	Schuppan D, Zimmer K-P The diagnosis and treatment of celiac disease. Dtsch Arztebl Int. 2013; 110: 835-46.
	In article
[6]	Guandalini S, Assiri A. Celiac disease: a review. JAMA Pediatr. 2014; 168: 272-8.
	In article		CrossRef
[7]	Kocna P, Vanickova Z, Zima T. Laboratory screening markers in gastroenterology--state of the art. Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub. 2013; 157: 91-7.
	In article
[8]	Gujral N1, Freeman HJ, Thomson AB. Celiac disease: prevalence, diagnosis, pathogenesis and treatment. World J Gastroenterol. 2012; 18: 6036-59.
	In article		CrossRef
[9]	Giersiepen K, Lelgemann M, Stuhldreher N, Ronfani L, Husby S, Koletzko S, Korponay-Szabó IR; ESPGHAN Working Group on Coeliac Disease Diagnosis. Accuracy of diagnostic antibody tests for coeliac disease in children: summary of an evidence report. J Pediatr Gastroenterol Nutr. 2012; 54: 229-41.
	In article		CrossRef
[10]	Lewis NR, Scott BB. Meta-analysis: deamidated gliadin peptide antibody and tissue transglutaminase antibody compared as screening tests for coeliac disease. Aliment Pharmacol Ther. 2010; 31: 73-81.
	In article		CrossRef
[11]	Vermeersch P, Geboes K, Mariën G, Hoffman I, Hiele M, Bossuyt X. Diagnostic performance of IgG anti-deamidated gliadin peptide antibody assays is comparable to IgA anti-tTG in celiac disease. Clin Chim Acta.2010; 411: 931-5.
	In article		CrossRef
[12]	Villalta D, Alessio MG, Tampoia M, Tonutti E, Brusca I, Bagnasco M, Pesce G, Stella S, Bizzaro N. Testing for IgG class antibodies in celiac disease patients with selective IgA deficiency. A comparison of the diagnostic accuracy of 9 IgG anti-tissue transglutaminase, 1 IgG anti-gliadin and 1 IgG anti-deaminated gliadin peptide antibody assays. Clin Chim Acta.2007; 382: 95-9.
	In article		CrossRef
[13]	Villalta D, Alessio MG, Tampoia M, Tonutti E, Brusca I, Bagnasco M, Pesce G, Bizzaro N. Diagnostic accuracy of IgA anti-tissue transglutaminase antibody assays in celiac disease patients with selective IgA deficiency. Ann N Y Acad Sci. 2007; 1109: 212-20.
	In article		CrossRef
[14]	Reeves GE, Squance ML, Duggan AE, Murugasu RR, Wilson RJ, Wong RC, Gibson RA, Steele RH, Pollock WK. Diagnostic accuracy of coeliac serological tests: a prospective study. Eur J Gastroenterol Hepatol. 2006; 18: 493-501.
	In article		CrossRef
[15]	Volta U, Granito A, Parisi C, Fabbri A, Fiorini E, Piscaglia M, Tovoli F, Grasso V, Muratori P, Pappas G, De Giorgio R. J Deamidated gliadin peptide antibodies as a routine test for celiac disease: a prospective analysis. Clin Gastroenterol. 2010; 44: 186-90.
	In article		CrossRef
[16]	Bizzaro N1, Tozzoli R, Villalta D, Fabris M, Tonutti E. Cutting-edge issues in celiac disease and in gluten intolerance. Clin Rev Allergy Immunol. 2012; 42: 279-87.
	In article		CrossRef
[17]	Rozenberg O, Lerner A, Pacht A, Grinberg M, Reginashvili D, Henig C, Barak M. A novel algorithm for the diagnosis of celiac disease and a comprehensive review of celiac disease diagnostics. Clin Rev Allergy Immunol. 2012; 42: 331-41.
	In article		CrossRef
[18]	Rozenberg O, Lerner A, Pacht A, Grinberg M, Reginashvili D, Henig C, Barak M.A new algorithm for the diagnosis of celiac disease. Cell Mol Immunol.2011; 8: 146-9.
	In article		CrossRef
[19]	Barak M, Rozenberg O, Froom P, Grinberg M, Reginashvili D, Henig C, Pacht A, Lerner A. Challenging our serological algorithm for celiac disease (CD) diagnosis by the ESPGHAN guidelines. Clin Chem Lab Med. 2013; 51; e257-259.
	In article		CrossRef
[20]	Agardh D. Antibodies against synthetic deamidated gliadin peptides and tissue transglutaminase for the identification of childhood celiac disease. Clin Gastroenterol Hepatol. 2007; 5: 1276-81.
	In article		CrossRef
[21]	Niveloni S, Sugai E, Cabanne A, Vazquez H, Argonz J, Smecuol E, Moreno ML, Nachman F, Mazure R, et al. Antibodies against Synthetic Deamidated Gliadin Peptides as Predictors of Celiac Disease: Prospective Assessment in an Adult Population with a High Pretest Probability of Disease. Lin Chem 2007; 53: 2186-2192.
	In article
[22]	Holding S, Wilson F, Spradbery D. Clinical evaluation of the BioPlex 2200 Celiac IgA and IgG Kits - A novel multiplex screen incorporating an integral check for IgA deficiency. J Immunol Methods. 2014; 405: 29-34.
	In article		CrossRef
[23]	Kocna P1, Vanícková Z, Perusicová J, Dvorák M. Tissue transglutaminase-serology markers for coeliac disease. Clin Chem Lab Med. 2002; 40: 485-92.
	In article
[24]	Tonutti E, Bizzaro N. Diagnosis and classification of celiac disease and gluten sensitivity. Autoimmun Rev. 2014; 13: 472-476.
	In article		CrossRef
[25]	Vermeersch P, Geboes K, Mariën G, Hoffman I, Hiele M, Bossuyt X. Serologicaldiagnosis of celiac disease: comparative analysis of different strategies. Clin Chim Acta. 2012; 413: 1761-7.
	In article		CrossRef
[26]	Swallow K, Wild G, Sargur R, Sanders DS, Aziz I, Hopper AD, Egner W. Quality not quantity for transglutaminase antibody 2: the performance of an endomysial and tissue transglutaminase test in screening coeliac disease remains stable over time. Clinical and Experimental Immunology, 2012; 171: 100-106.
	In article		CrossRef
[27]	Matthias T, Neidhöfer S, Pfeiffer S, Prager K, Reuter S, Gershwin ME. Novel trends in celiac disease. Cell Mol Immunol. 2011; 8: 121-5.
	In article		CrossRef
[28]	Matthias T, Pfeiffer S, Selmi C, Eric Gershwin M. Diagnostic challenges in celiac disease and the role of the tissue transglutaminase-neo-epitope. Clin Rev Allergy Immunol.2010; 38: 298-301.
	In article		CrossRef
[29]	Tozzoli R, Kodermaz G, Tampoia M, Visentini D, Tonutti E, bizzaro N. [detection of autoantibodies specific for transglutaminase-gliadin peptides complex: a new way to explore the celiac iceberg.] It J Lab Med. 2010; 6; 28-35.
	In article
[30]	Remes-Troche JM, Ramírez-Iglesias MT, Rubio-Tapia A, Alonso-Ramos A, Velazquez A, Uscanga LF. Celiac disease could be a frequent disease in Mexico: prevalence of tissue transglutaminase antibody in healthy blood donors. J Clin Gastroenterol. 2006; 40: 697-700.
	In article		CrossRef
[31]	Remes-Troche JM, Rios-Vaca A, Ramírez-Iglesias MT, Rubio-Tapia A, Andrade-Zarate V, Rodríguez-Vallejo F, López-Maldonado F, Gomez-Perez FJ, Uscanga LF. High prevalence of celiac disease in Mexican Mestizo adults with type 1 diabetes mellitus. J Clin Gastroenterol. 2008; 42: 460-5.
	In article		CrossRef
[32]	Tozzoli R, Kodermaz G, Porcelli B et al. Clinical relevance and diagnostic accuracy of new ELISA method for the detection of autoantibodies to gliadin-transglutaminase complex. Proceedings of the 7thInternational Congress on autoimmunity, Ljubljana, 5-9 May, 2010.
	In article
[33]	Tonutti E, Visentini D, Fabris M et al. Antibodies to the transglutaminase-deamidated gliadin complex: a new serological approach to the diagnosis of celiac disease.Proceedings of the 7thInternational Congress on autoimmunity, Ljubljana, 5-9 May, 2010.
	In article
[34]	Lytton SD, Antiga E, Pfeiffer S, Matthias T, Szaflarska-Poplawska A, Ulaganathan VK, Placek W, Fabbri P, Hall R, Caproni M.Neo-epitope tissue transglutaminase autoantibodies as a biomarker of the gluten sensitive skin disease-dermatitis herpetiformis. Clin Chim Acta. 2013; 415: 346-349.
	In article		CrossRef