Helicobacter pylori (or H. pylori) is a small but mighty bacterium that causes one of the most common bacterial infections worldwide. H. pylori infects approximately two-thirds of the world’s population and is implicated in gastrointestinal (GI) disorders like gastritis and peptic ulcer disease (PUD).
H. pylori has been designated as a carcinogen by the World Health Organization (WHO) and is the primary risk factor leading to gastric cancer.
This article aims to empower healthcare practitioners and their patients by introducing the various non-invasive and invasive testing modalities available to diagnose an H. pylori infection. Precise diagnosis of H. pylori is critical to guide effective treatment strategies and improve health outcomes.
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Understanding H. pylori Infection
H. pylori is a microaerophilic (thrives in environments with low oxygen levels), gram-negative, spiral-shaped bacterium found in the stomach. H. pylori is commonly acquired during childhood and persists throughout life while remaining clinically silent. Transmission occurs through the oral-oral and fecal-oral routes. Its prevalence is highest in developing countries with low socioeconomic status.
H. pylori can withstand the harsh environment of the stomach, where it readily colonizes the gastric mucosa, leading to immune-mediated inflammation.
If left untreated, an active H. pylori infection can quickly progress from mild-moderate chronic or atrophic gastritis and peptic ulcer disease to more serious mucosa-associated lymphoid tissue (MALT) lymphoma and gastric adenocarcinoma. An accurate diagnosis of H. pylori infection is critical in developing an effective treatment strategy and to prevent disease progression.
Non-Invasive Tests for H. pylori
The following testing options are considered non-invasive:
Urea Breath Test (UBT)
The UBT is widely used for the initial diagnosis of an H. pylori infection in the stomach. It is regarded as the most accurate non-invasive test, with a high sensitivity of 95.9% and a specificity of 95.7%. UBT is a convenient and safe test used in an outpatient clinical setting.
Urease is an enzyme unique to H. pylori. H. pylori uses the urease enzyme to break down urea into ammonia and carbon dioxide (CO2). CO2 is exhaled through the lungs. The UBT utilizes a urea solution with a radiolabeled carbon (C).
The patient ingests the solution, and if H. pylori is present in the stomach, the urease enzyme breaks down the urea solution. After 20 to 30 minutes, the CO2 exhaled by the patient is collected, and the presence of radiolabeled C is measured and quantified. A positive UBT indicates the presence of an ongoing H. pylori infection.
Stool Antigen Test (SAT)
Like the UBT, the SAT also has high sensitivity and specificity and is used for the initial diagnosis of an H. pylori infection in the stomach.
The SAT detects H. pylori antigens (proteins produced by bacteria) in the stool. In individuals with an active infection, H. pylori is excreted in the feces.
An immunological method known as enzyme-linked immunosorbent assay (ELISA) containing monoclonal antibodies against the H. pylori antigens is used on the stool sample collected from the patient. A positive SAT indicates an active H. pylori infection in the stomach.
Serology (Blood) Testing
Serology testing detects the presence of antibodies against H. pylori in blood using ELISA. IgG antibodies are produced in our blood as part of an immune response to an H. pylori infection. These antibodies can persist in our bloodstream long after an infection has resolved.
Therefore, unlike the UBT and SAT, this test is unreliable in a clinical setting as it may provide a false negative result. Serology testing is primarily used for epidemiological studies because it is more widely available.
Invasive Tests for H. pylori
The following testing options are more invasive:
Endoscopy with Biopsy
The gold standard to diagnose an H. pylori infection is an esophagogastroduodenoscopy (EGD) (or upper GI endoscopy) with a biopsy of the gastric mucosa followed by a rapid urease test (RUT), histopathology, culture, or polymerase chain reaction (PCR) on biopsy samples.
Rapid Urease Test (RUT)
The RUT involves transferring the biopsy specimen to a medium containing urea and a pH indicator. If H. pylori is present in the biopsy, the urease enzyme metabolizes urea into ammonia and CO2. The ammonia will raise the pH of the medium and change the color of the indicator within 24 hours. If no change in the color of the pH indicator is observed an alternative test must be performed to confirm the results.
Histology
Histopathological examination is sometimes considered the gold standard to detect an active H. pylori infection; a minimum of three biopsies is encouraged for an accurate diagnosis. Specialized stains such as hematoxylin & eosin (H&E) and Giemsa are used to stain the gastric biopsy specimen and directly visualize the bacteria under a microscope.
Visualization of curved bacteria under the microscope confirms the presence of H. pylori. Histology is an excellent tool for observing pathological changes to the surrounding tissue including inflammation or malignant changes.
Culture
A culture includes inoculating the gastric biopsy specimen in a medium that facilitates the growth of H. pylori. It has 100% specificity. A positive culture is adequate to confirm an active H. pylori infection.
Culture is not routinely performed due to its low sensitivity, expense, and time-consuming nature. It is often reserved to characterize antibiotic susceptibility and detect antibiotic resistance if treatment failure is suspected.
Polymerase Chain Reaction (PCR)
PCR is a technique that amplifies two or more target DNA sequences of H. pylori obtained from a gastric biopsy sample to detect an active infection. It is a fast and efficient method with a high sensitivity and specificity (> 95%) for H. pylori. However, PCR is reserved for epidemiological research and identifying mutations associated with antimicrobial resistance.
Table 1 provides a comprehensive overview outlining the advantages and disadvantages of the non-invasive and invasive diagnostic approaches to detect an H. pylori infection in the stomach.
Selecting the Appropriate Lab Test
An H. pylori infection is often asymptomatic. The decision to test for H. pylori should only be made with therapeutic intent for clinically symptomatic individuals.
Non-invasive Methods
Non-invasive diagnostic methods such as UBT and SAT are preferred for the initial diagnosis of H. pylori infection due to their high sensitivity and specificity. UBT and SAT are also used to determine treatment response and eradication of H. pylori infection:
- UBT: 4 weeks post-treatment
- SAT: 3 months post-treatment
Invasive Methods
GI symptoms such as dyspepsia, abdominal pain, nausea, and vomiting may be indicative of an underlying gastrointestinal disorder including gastritis or peptic ulcer disease where H. pylori is implicated. Invasive diagnostic methods are preferred when clinical symptoms suggest an H. pylori infection. Endoscopy allows the concurrent visualization of the gastric mucosa for chronic inflammation, ulceration, bleeding, or cancerous tissue changes.
Challenges in H. pylori Detection
Diagnosing an H. pylori infection can be challenging as each diagnostic test discussed in this article has its sensitivity, specificity, and limitations (see Table 1). Accurate diagnosis is critical in developing a successful treatment regimen to prevent the chronic inflammation of the gastric mucosa.
Treatment with antibiotics (including bismuth-containing antimicrobials) and PPIs (medications that reduce stomach acid secretion) prevents the growth of H. pylori and suppresses its urease activity. The rate of false-negative results with UBT and SAT in patients on PPIs is between 10% and 40%.
Therefore, PPIs, antibiotics, and bismuth compounds should be discontinued at least 2 – 4 weeks before testing for H. pylori infection with UBT and SAT to prevent false-negative results. Similar false-negative results may occur with endoscopic biopsy for RUT, histopathology, and culture due to low bacterial load. Acute GI bleeding can also lead to false-negative results.
False-positive results for diagnosing H. pylori is rare, but may occur if other urease-producing bacteria such as H. heilmannii is present in the stomach.
Emerging Technologies and Future Directions
New research and technological advancements aim to overcome existing challenges in detecting H. pylori with more accurate and patient-friendly methods.
Molecular diagnostic techniques such as PCR-based detection have excellent sensitivity and specificity for H. pylori. Specific target genes, including UreA, glmM, UreC, 16S rRNA, 23S rRNA, HSP60, and VacA genes, have been isolated to accurately detect H. pylori. Selecting two or more target genes increases the specificity. Concurrently, PCR can detect gene mutations leading to antibiotic resistance, thus guiding personalized treatment strategies.
In addition to PCR, the evolution of bioinformatics analysis has helped select more suitable antigens for serological (blood) testing. These new antigens have high immunogenicity and elicit specific antibodies that fade away quickly after eradication of H. pylori.
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Key Takeaways
- Helicobacter pylori (H. pylori) is a bacterium found in the stomach that can lead to chronic inflammation of the gastric mucosa leading to gastritis, peptic ulcer disease, and gastric cancers.
- Accurate diagnosis is vital to the timely initiation of antibiotic treatment and the successful eradication of an underlying H. pylori infection.
- Non-invasive diagnostic tests for H. pylori include urea breath test (UBT), stool antigen test (SAT), and serology (blood) testing.
- Invasive diagnostic tests for H. pylori include endoscopic biopsy followed by rapid urease test (RUT), histology, culture, or PCR.
- Here is a quick guide for selecting an appropriate diagnostic method:some text
- Asymptomatic Patient:some text
- Do not test; diagnostic screening is unwarranted.
- Symptomatic Patient:some text
- < 50 years old: initial diagnosis with UBT or SAT
- > 50 years old: initial diagnosis with UBT or SAT, followed by endoscopic biopsy with RUT or histologic staining
- Confirm the eradication of H. pylori with UBT or SAT
- Asymptomatic Patient:some text
- PPIs, antibiotics, and bismuth compounds should be discontinued at least 2 to 4 weeks before testing for an H. pylori infection.
- Healthcare practitioners are encouraged to stay up-to-date on the current guidelines and advancements in diagnostic approaches for the timely identification of an H. pylori infection to employ effective treatment strategies and prevent disease progression.
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