Antibodies to Helicobacter pylori CagA, IgG

A comprehensive analysis designed to detect H. pylori in patients with suspected gastritis, gastric ulcer, or duodenal ulcer, including the main serological tests and the RT-PCR method.

H. pylori is a Gram-negative, facultative anaerobic microorganism capable of infecting the mucosa of the stomach and duodenum. In most cases, H. pylori infection (helicobacteriosis) is persistent and chronic. Helicobacteriosis is very common: H. pylori can be detected in approximately 50% of the world’s population. However, H. pylori-associated diseases (gastritis, gastric or duodenal ulcer, gastric adenocarcinoma, MALT lymphoma) develop in only 15–20% of infected individuals. A key feature of these diseases is their favorable prognosis when early diagnosis and complete eradication of H. pylori are achieved. Laboratory diagnostic methods play a leading role in the diagnosis of helicobacteriosis.

There are several methods for detecting H. pylori. Direct methods allow the microorganism itself to be identified. Most direct methods require a sample of the mucosal tissue (biopsy) and/or gastric or duodenal contents (aspirate), which are usually obtained during endoscopic examination. Therefore, direct diagnostic methods are generally invasive. In contrast, indirect methods detect not the microorganism itself but indirect signs of infection, such as specific antibodies in blood serum (serological tests) or the presence of labeled carbon in exhaled air (urea breath test). Since indirect tests do not require endoscopic examination, they are considered non-invasive. Both direct and indirect tests for H. pylori have their advantages and limitations. Accurate diagnosis of helicobacteriosis requires the use of several tests simultaneously. For this reason, a comprehensive analysis that includes all necessary H. pylori tests is particularly convenient for both physicians and patients.

One of the most sensitive methods for detecting H. pylori is real-time polymerase chain reaction (RT-PCR). RT-PCR is a molecular diagnostic method that allows detection of fragments of the pathogen’s genetic material (DNA) in biological samples (for example, tissue specimens). Because the analysis is based on the detection of genetic material, RT-PCR can identify the presence of any form of H. pylori (not only active spiral forms but also inactive coccoid, non-cultivable forms), resulting in very high sensitivity that exceeds that of bacteriological culture. Theoretically, the presence of a single DNA molecule is sufficient for RT-PCR detection. In practice, the pathogen concentration in the sample should be approximately 10–100 CFU/mL. Such high sensitivity means that a negative test result allows H. pylori to be excluded as the cause of disease, which is particularly important in the differential diagnosis of NSAID-associated, stress-related, and ischemic gastritis and ulcers.

It should be noted that despite the very high sensitivity of the test (85–98%), false-negative results are still possible. For example, a false-negative result may occur when the bacterial load is very low, such as during treatment with certain antibiotics. Diagnostic errors can be avoided by combining this direct test with serological studies.

H. pylori infection is accompanied by a significant increase in IgG and IgA immunoglobulins in blood serum. These immunoglobulins (antibodies) are detected using indirect tests. IgG antibodies are found in 95–100% of helicobacteriosis cases, while IgA antibodies are detected in 68–80%. The test allows determination of antibody titers and is therefore quantitative. As a rule, high antibody titers are more characteristic of active, ongoing infection. However, there is no clear correlation between antibody titer levels and the severity of infection.

Serological tests, like RT-PCR, also have certain limitations. Test results depend on the patient’s immune response. Patients receiving cytostatic therapy and elderly individuals often have a reduced production of specific antibodies (including antibodies to H. pylori). For this reason, to avoid diagnostic errors, serological tests should be supplemented with direct diagnostic methods. This feature was taken into account when designing the comprehensive H. pylori analysis.

Thus, the comprehensive H. pylori analysis represents a combination of necessary and sufficient tests for detecting this microorganism. This comprehensive test is not intended for treatment monitoring. The results of both RT-PCR and IgG/IgA immunoglobulin testing may remain positive even after complete eradication of H. pylori. False-positive RT-PCR results in this case are due to the ability of the method to detect DNA from any microorganisms, including destroyed ones, while false-positive serological results are explained by the characteristics of immune response dynamics.

Recommendations: We recommend avoiding physical exertion before sample collection. During the 10–20 minutes of sample collection, try to remain relaxed. Postpone testing immediately after paraclinical examinations (X-ray, CT, MRI) and physiotherapy procedures, as they may affect test results.