Generality
Gastric mucosa infection by Helicobacter pylori results in a systemic (IgM, IgG) and local (IgA) immune response .
The antibody response to infection is greater the higher the bacterial load; consequently, it is possible to measure specific antibodies, in the patient's blood, to identify any colonization with Helicobacter pylori.
Anti-Helicobacter pylori antibodies
The serological research of anti-Helicobacter pylori antibodies can now be considered the preferred method for the search for infection; it is, in fact, a first-level investigation, simple and more economical than other invasive methods - such as histology or rapid urease test on bioptic samples of gastric mucosa - and non-invasive, such as urea breath test and the detection of Helicobacter pylori antigens in faeces.
The serological test for anti-Helicobacter pylori antibodies is therefore indicated for the rapid screening of very large populations, also useful for the early diagnosis of infection, since the antibody titers tend to positivize even before the clinical manifestation of the disease.
What's this
Helicobacter pylori is a Gram-negative, spiral-shaped bacterium with flagella. This organism colonizes the mucous membrane of the stomach, irritating its walls.
In addition to evoking a local immunological reaction (IgA), the antigenic components of Helicobacter pylori induce a humoral systemic response, producing specific antibodies (IgM, IgG). The concentration of the latter is much higher, the greater the bacterial load and tends to disappear or reduce after the eradication of the infection.
Why do you measure
Serological research of anti-Helicobacter pylori antibodies helps to diagnose the presence of this bacterium in the stomach. The doctor may indicate this examination in the face of disorders such as acidity and difficulty in digestion.
This is a fairly rapid test, but it does have some limitations: if the person has the infection, it can be positive even if the infection has been treated and eradicated. Furthermore, the antibody titre tends to decrease very slowly after the eradication of the bacterium, so the IgG dosage is of limited utility in assessing the result of the eradicating treatment immediately after the end of the therapy.
Practically:
- If the test result is negative, there is a reasonable certainty that the patient will NOT have an infection with Helicobacter pylori;
- If the result is positive, it is not possible to make a distinction between an existing or previous infection.
For this reason, the research in the blood of antibodies against Helicobacter pylori is a little used analysis.
Associated examinations
Non-invasive laboratory tests that can certainly diagnose the presence of Helicobacter pylori in the stomach are the urea breath test and the search for bacterium antigens in the faeces.
These investigations can be associated with invasive methods, such as histology after gastroscopy or rapid urease test on biopsy specimens of gastric mucosa.
Normal values
Normally, the outcome of the search for anti-Helicobacter pylori antibodies must be negative.
REFERENCE VALUES:
- Negative result: antibody titre less than 0.90 U / ml;
- Border-line result: antibody titer between 0.90 and 1.09 U / ml;
- Positive result: antibody titer equal to or greater than 1.10 U / ml.
In any case, it is important that the results of the analyzes are assessed as a whole by the medical doctor, who knows the patient's medical history.
Antibodies High - Causes
When the research in the blood of antibodies against Helicobacter pylori gives a positive result, it means that the person has contracted the infection. The quantity of antibodies is much higher, the greater the bacterial load and tends to disappear or reduce (albeit slowly) after the eradication of the bacterium.
Low antibodies - Causes
The absence of antibodies against Helicobacter Pylori is not usually associated with medical problems and / or pathological consequences; therefore, it is not considered clinically relevant.
How to measure it
The search for anti-Helicobacter pylori antibodies is carried out through a simple blood sample.
Preparation
To perform blood sampling for the detection of anti-Helicobacter pylori antibodies, no special preparation is required and fasting is not necessary.
Interpretation of Results
The serological research of anti-Helicobacter pylori antibodies can be considered a first-level investigation, simple and inexpensive compared to other methods used to diagnose an infection of the gastric mucosa by the bacterium.
The detection in the blood of anti-Helicobacter pylori antibodies is not indicative of an ongoing infection, as it could also be due to previous infections.
If the analysis is negative, it is unlikely that the patient has been infected; in case of a positive result, it is still necessary to carry out a confirmation test by means of the breath test or the search for fecal antigen.
Reliability and limits of the test
Unfortunately the search for anti-Helicobacter pylori antibodies in serum has some important limitations, given by the fact that the antibody titers remain high until about three years after the eradication of the infection; consequently, a positive blood test does not allow us to establish whether the infection is still in progress or whether it has been in the past. On the other hand, when the test is negative, there is a reasonable certainty that the patient is not a carrier of a Helicobacter pylori infection.
Despite the excellent levels of sensitivity and specificity, the main limitation of serological research tests for anti-Helicobacter pylori antibodies lies in the inability to distinguish a current infection from a previous one.
For the same reason the titer of anti-Helicobacter pylori serum antibodies cannot be used to evaluate the efficacy of the medical therapy undertaken; as a matter of fact, the antibody titer is slowly reduced and can remain high even for a long time after the Helicobacter has been eradicated. For this clinical application the aforementioned breath tests and the search for faecal antigens of Helicobacter pylori are much more suitable.
