Helicobacter pylori is a common, spiral-shaped bacterium that colonizes the lining of the stomach. While it causes no symptoms for many individuals, it can lead to chronic inflammation. The H. pylori Immunoglobulin G (IgG) test is a blood-based method used to determine if a person has been exposed to this bacterium. This serological test detects the specific antibodies the body produces in response to H. pylori.
The Bacterium and the Antibody Response
When the body encounters H. pylori, the immune system produces several types of antibodies. Immunoglobulin G (IgG) is the most abundant antibody in the blood and plays a role in long-term immune memory. Detecting IgG indicates the body has mounted a sustained immune response to the bacterium’s antigens, such as urease, CagA, and VacA.
IgG antibodies are produced after the initial, acute phase of infection and can persist in the bloodstream for a long time. This makes the IgG test a reliable indicator of past or current exposure to H. pylori. While other antibodies, like Immunoglobulin M (IgM), are transient and produced early in an infection, IgG is a better marker for chronic infections, which is typical of H. pylori.
Clinical Reasons for H. pylori IgG Testing
A physician may order an H. pylori IgG test when a patient presents with symptoms suggesting gastrointestinal irritation or disease. The test is often used in the initial investigation of chronic dyspepsia, which includes recurrent symptoms like upper abdominal pain, bloating, and nausea.
Testing is also indicated for patients with a history of peptic ulcers, as H. pylori is a major cause of these sores. The test is sometimes used for patients with unexplained iron deficiency anemia or those with a family history of gastric cancer. Since the serology test is non-invasive, requiring only a blood draw, it is a convenient tool for initial screening.
Interpreting Your IgG Test Results
The result of an H. pylori IgG test is reported as negative, positive, or sometimes indeterminate (equivocal). A negative result suggests the patient has not been infected with the bacterium. A positive result indicates that IgG antibodies were detected, confirming the immune system has encountered H. pylori at some point.
The primary limitation of the IgG test is its inability to distinguish between a current, active infection and a resolved, past infection. Since IgG antibodies can remain elevated for months or years after the bacterium has been eliminated, a positive result does not confirm the presence of live bacteria. Therefore, a positive IgG test is interpreted as evidence of exposure, not definitive proof of an active infection causing symptoms.
If a patient tests positive for IgG and has current symptoms, a physician will often order a follow-up test to confirm an active infection. Due to the long-term persistence of the antibody, the IgG test is not recommended for confirming eradication after treatment. For this purpose, other non-invasive diagnostic tools are preferred, such as the urea breath test or the stool antigen test, as these detect the presence of the living bacterium.
Treatment and Follow-Up for H. pylori Infection
When an active H. pylori infection is confirmed, standard treatment involves a combination of medications designed to eradicate the bacteria. This approach, often called triple therapy, commonly consists of two antibiotics and a proton pump inhibitor (PPI). The antibiotics kill the bacteria, while the PPI reduces stomach acid production, aiding in stomach lining healing and enhancing antibiotic effectiveness.
Adherence to the full medication course, which typically lasts 10 to 14 days, is important for treatment success. After the antibiotic regimen is complete, follow-up testing is necessary to ensure the infection has been eradicated. This follow-up is conducted at least four to six weeks after finishing the antibiotics to allow the body time to clear the remaining bacteria. The preferred methods for confirming eradication are the urea breath test or the stool antigen test, which reliably indicate the absence of active bacteria.