Dr. Kenneth Fine Comments on this Study:
Dont Throw the Baby Out With the Bath Water!
Letter to the Editor BMJ
Kamran Rostami, M.D., Ph.D. Department of Medicine, Gloucestershire Royal Hospital Gloucester, UK
Kenneth Fine, M.D. The Intestinal Health Institute, Dallas, Texas, USA
We have read with interest the article by Kappler et al recently published in your journal (1) and feel several issues deserve mention. This article is very timely in light of the growing worldwide awareness of immunologic sensitivity to dietary gluten and celiac disease, as well as appreciation of its high prevalence; these facts are driving the need for more widely available, low cost, non-invasive screening tests. Stool testing for these disorders holds great promise for screening because it does not require any invasion of body tissues, is of relatively low cost, and could be widely available combining medical care delivery of such tests with home testing.
While our first criticism of this study is its small cohort size (20 patients), the results are intriguing, but in our opinion have been misinterpreted by the authors. First, there is a potential methodological flaw in this study whereby a serologic method was apparently transferred intact to analyze stool. The aspects of a serologic ELISA method possibly requiring modification for use in stool include but are not limited to: degree to which the sample is diluted prior to analysis; technique and amount of washing of plates during ELISA analysis (because of greater solid contaminant of fecal fluid vs. serum); mathematical conversion of detected optical density to a Unit; and how that calculated Unit is interpreted relative to a normal vs. abnormal cutoff. Utilizing fecal antigliadin and antitissuetransglutaminase IgA antibody testing in this way were reported to be very insensitive (6-10%) but highly specific (97-98%) for celiac disease. Such results should be interpreted as possibly possessing either a misassigned cutoff value (i.e., one that was too high), or possibly introduction of an artificial element that drove fecal antibody concentrations down (such as over-diluting the stool, improper handling or storage of specimens allowing ex vivo destruction of antibody, or centrifuging the stool at the wrong speed driving antibody into the pellet; the authors mentioned destruction of antibody during transit within the GI tract, but antibody is very stable within the GI tract, and has been detected in stool by many authors). Nevertheless, as performed in this study, such a highly specific stool test for celiac disease could be used as a pre-screening test of sorts, able to specifically and non-invasively detect celiac disease, perhaps with a home collected stool specimen. At the worst, 6-10% of celiac patients could be identified even before presenting to a medical institution.
The authors went on to correct a potential cutoff error, using optimization of cut-off limits by receiver operating characteristic analysis, and found that resetting the cut-off value and combining the tests could possess an 82% sensitivity and 58% specificity. Again the authors discounted these findings, in our opinion failing to grasp their importance. Although they did not report the corrected accuracy results of antigliadin test alone, their stool test may have outperformed serum antigliadin antibody, the serologic test in longest use in screening for celiac disease. Many investigators have lost confidence in the presumed lack of specificity of antigliadin antibody alone as a screening test for celiac disease because of the paradigm within which it has been applied, that is, villous atrophic celiac disease. It is also known that its sensitivity is highly dependent on the degree of small intestinal villous atrophy present (2). Most importantly today however, in our opinion, with the wealth of expanding knowledge on the broadening clinical spectrum of gluten-sensitive disorders (3), it should at least have been considered and/or discussed by Kappler et al that in their optimized cut-off analysis, a positive fecal antigliadin antibody may have been a true sign of immunologic sensitivity to gluten either in an evolutionary phase before the onset of villous atrophic celiac disease (4), or in gluten sensitive individuals who may never develop classic celiac disease but who suffer symptoms and associated autoimmune disorders nevertheless. When interpreted in this context, the authors results may have been clinically important. We feel further study of this method with improved attention to methodological issues pertaining to stool, and broader clinical application beyond classic celiac disease is warranted.
1. Kappler M, Krauss-Etschmann S, Diehl V, Zeilhofer H, Koletzko S. Detection of secretory IgA antibodies against gliadin and human tissue transglutaminase in stool to screen for celiac disease in children: validation study. BMJ. 2006 January 28; 332(7535): 213-14.
2. Rostami K, Kerckhaert J, Tiemessen R, von Blomberg BM, Meijer JW, Mulder CJ. Sensitivity of antiendomysium and antigliadin antibodies in untreated celiac disease: disappointing in clinical practice. Am J Gastroenterol. 1999 Apr;94(4):888-94.
3. Ferguson A, Arranz E, OMahony S. Clinical and pathological spectrum of celiac disease--active, silent, latent, potential. Gut. 1993 Feb;34(2):150-1.
4. Arranz E, Ferguson A. Jejunal fluid antibodies and mucosal gamma/delta IEL in latent and potential celiac disease. Adv Exp Med Biol. 1995;371B:1345-8.