Detection of antibodies against Helicobacter pylori

Sensitivity and specificity of the H. pylori test

Antibodies against Helicobacter pylori in the serum can be detected by various immunological and serological techniques such as immunoblotting, immunofluorescence, hemagglutination, complement fixation, latex agglutination test and others. However the most common method is indisputably ELISA – it is a simple, fast, cheap and reliable technique. However, the specificity and sensitivity of the method is highly dependent on the antigen used – from the whole cells, through the ultrasound sonicate, glycine extract to protein purification. In 1989, HM-CAP, high molecular weight cell-associated protein, were isolated with a sensitivity and specificity of 95 %.

Serological detection of antibodies to Helicobacter pylori is of clinical importance especially for for long term observation after treatment and for monitoring the success of Helicobacter pylori eradication. The decrease of the IgG to < 50 % after 6 months of the treatment shows specificity of 95 % and sensitivity 97 %. Indications include screening patients who are at risk, such as kidney transplant patients , where helicobacter infection increases the risk of peptic ulcer and bleeding.

Antibodies against Helicobacter pylori can be also detected in saliva and urine samples by immunological methods. There are many rapid tests which detect antibodies against Helicobacter. For example, by performing capillary blood sampling of whole blood, and with the use of immunoaffinity chromatography, we get the result after a couple of minutes. Sensitivity and specificity of these tests are relatively low – 70-85 %.

The serological diagnosis of antibodies to Helicobacter pylori also includes the detection of cagA, vacA and iceA antigens, the presence of which specifies Helicobacter pylori strains with higher pathogenicity. These antigens are detected with help of classic ELISA tests on the microtiter plates or PCR techniques. Demonstration of Helicobacter pylori and its strains by PCR methods is in the phase of clinical testing, it is not used in routine diagnostics yet. The diagnostic significance of the determination of antibodies to Helicobacter pylori is still the subject of research, it is not suitable for screening programs.

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References

• with permission of the author adapted from KOCNA, Petr. GastroLab : MiniEncyklopedie laboratorních metod v gastroenterologii [online]. ©2002. The last revision 2011-01-08, [cit. 2011-03-04]. <http://www1.lf1.cuni.cz/~kocna/glab/glency1.htm>.

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