**4.** *H. pylori* **diagnostic tests in FD**

Tests to diagnosis *H pylori* infection are divided into those that are invasive requiring endos‐ copy versus those that are noninvasive, not requiring endoscopy. The choice of test depends on issues such as cost (variable in each country), availability, clinical situation, prevalence of infection, pretest probability of infection, and presence of confounding factors (eg, the use of PPI and antibiotics) that may influence test results.

**a.** Noninvasive tests for *H. pylori*

The noninvasive tests available in clinical practice include serologic tests, urea breath tests, and stool antigen tests. The choice of test is important in terms of validity

**1.** Serological tests

survey of 2,488 adult subjects identified an overall *H. pylori* infection at 40.2% that was no different in dyspeptic subjects compared to asymptomatic persons. Differences amongst geographic regions likely related to differences in socioeconomic status and community hygiene during childhood period. [8] The frequency of functional dyspepsia is common in Asia, varying between 8-23% in most reported studies. [10] In fact, given the common frequency of *H. pylori* infection and challenges in obtaining endoscopy to eliminate organic causes of dyspepsia, it is difficult to discern the extent this microorganism is the basis for

There are many FD patients in Asian as well as Western countries. The reported prevalence of *H. pylori* infection in patients with FD varies from 39% to 87%. [14] Several epidemiological studies have shown that *H. pylori* infection occurs more frequently in FD than in matched control populations. A meta-analysis published in 1999 reported a summary odds ratio for *H.*

**3. Pathogenesis of functional dyspepsia associated with** *H. pylori* **infection**

The pathophysiological disturbances generally responsible for the dyspepsia focus on hyperacidity, impaired gastric accommodation (the "stiff fundus") and delayed gastric emptying. FD patients who are infected with *H. pylori* have higher stimulated gastric acid secretion than *H. pylori*-negative healthy volunteers. [16] Impaired accommodation to a meal may be common in functional dyspepsia and early satiety, but is not particularly associated with *H. pylori* positivity or delayed gastric emptying. There is no constituent disturbance of sensory or motor function yet reported in H. pylori-infected persons. Another factor possibly responsible for the dyspepsia associated with H. pylori infection is the gut hormone, ghrelin. Secreted from oxyntic cells, ghrelin normally stimulates gastric motility and food intake. Patients with *H. pylori* may have reduction in ghrelin secretion that might lead to impaired

Recent study demonstrated that metronidazole resistant strains of *H. pylori* infection were significantly higher in PDS than those of EPS patients. This study also indicated more specific of *cagA* genotype that presence of *cagA 2a* gene of *H. pylori* infection was significantly higher in metronidazole resistant than those of metronidazole sensitive strains especially in EPS patients. This finding might be helpful to identify metronidazole resistant by using *cagA*

*CagA* is a highly immunogenic protein encoded by the *cagA* gene, located at end of the *cag* pathogenicity island (PAI). Infection with *cagA*-positive strains was associated with a greater inflammatory response and an increased risk of adverse clinical outcomes than with *cagA*negative strains. [7, 18-20] Taneike et al recently reported that the metronidazole resistant rate in *cagA* negative group was significantly higher than in *cagA* positive group and suggested that absence of *cagA* might be a risk factor in development of metronidazole resistance. [21] Unlike many countries such as European countries and United State of America, nearly all of *H. pylori* strains in Thailand possess *cagA*-positive strains. [16] These different results might be

dyspepsia in Asia. [10, 11]

58 Dyspepsia - Advances in Understanding and Management

*pylori* infection in FD of 1.6 (95% CI, 1.4 to 1.8). [15]

gastric emptying and symptoms of postprandial dyspepsia.

genotype in dyspeptic patients. [17]

IgM and IgA antibody tests have not proven to be useful clinically, whereas anti–*H pylori* IgG has a better result. anti–*H pylori* IgG usually can be detected by 3-4 weeks after infection. The three mains methods of commercial kits are ELISA (\$90–\$95/correct diagnosis),, immunochro‐ matography, and Western blotting.

Most serologic tests carries a high sensitivity (~90 to 100%), but variable specificity (under 85-90%). Their positive and negative predicative values depend upon the background prevalence of *H. pylori* infection in the population at risk. In areas where infection is common, a negative test is likely to be a false negative. Conversely, a positive test amongst those in whom *H pylori* is infrequent is more likely to be a false positive. In developed countries with low prevalence of *H. pylori* infection (<20%), for example, a positive serological test signals active infection only about half the time. Hence, serology should be validated locally. Further, antibody tests can remain positive for years after *H pylori* eradication and have limited value to confirm eradication of *H pylori* infection4.

**2.** Urea breath test (UBT)

The urea breath test provides a reliable noninvasive method for *H pylori* detection with sensitivity and specificity of 88-95% and 95%-100% respectively. [33] Urea breath testing is not only sensitive and specific but has an important advantage to confirm *H pylori* eradication. Following ingestion of 13C- or 14C-urea, *H pylori*-produced urease enzyme that is resident in the stomach hydrolyzes this labeled urea to 14CO2 or 13CO2, which can be detected in breath samples [34] (fig. 1). The nonradioactive13C (a stable label) test and the radioactive 14C test have received US Food and Drug Administration (FDA) approval for *H pylori* diagnosis. The dose of radiation in the 14C-urea test however is not approved for use in children and pregnant women [4].

(A) (B)

Functional Dyspepsia and *Helicobacter pylori* Infection

http://dx.doi.org/10.5772/56652

61

**Figure 3.** A.) *H pylori* detected by histology; (B.) *H pylori* detected by rapid urease test

Histological examination has an advantage over other diagnostic tests by providing morpho‐ logical information such as severity of gastritis, and evidence for dysplasia. The accuracy of histological examination however may be variable due to density of *H. pylori* and sampling error, and is dependent upon histopathogical interpretation. The accuracy of histological diagnosis of *H pylori* infection can be improved by adequate biopsies from the antrum and

Rapid urease tests contain a solution or gel with urea and a pH indicator reagent. The presence of urease from *H pylori* results in hydrolysis of neutral urea to alkaline ammonia, which is then visualized by a change in color of the pH indicator. The rapid urease test has a high sensitivity

Any concomitant use of antibiotics or PPI however will reduces bacterial load, and may lead

Proposed strategies based on the noninvasive diagnosis of H. pylori infection so-called ''testand-treat'' strategy. This strategy has been proposed for clinical practice in developed countries which has low prevalence of H. pylori infection. Test-and-treat is based on the test of the presence of H. pylori and its subsequent eradication when detected.13 The test-andscope strategy performing a test to detect H. pylori in all patients and endoscopy only in those who are shown to be infected has been considered useful in clinical practice in some developing

body and by special staining such as a silver staining and the Diff-Quik stain [35].

(95%) and specificity (95%), [36] making it an excellent primary diagnostic test.

to false negative tests such as rapid urease tests, urea breath test and histology. [4]

countries which has high prevalence of H. pylori infection such as Asia.

**4. Test-and-Treat Strategy for** *H. pylori*

#### **3.** Fecal *H. pylori* detection

*H. pylori* in the stomach also appears in the stool, allowing the development of fecal assays: *H pylori* culture, DNA detected by polymerase chain reaction (PCR), or *H pylori* antigen testing. Only stool antigen has proven to be clinical useful with sensitivities and specificities of more than 90%. Stool antigen assay is advantageous to confirm eradication. To avoid false negative results, it is generally recommended that post-treatment testing with the UBT, histology, stool antigen test or culture be delayed for 4 weeks and the patients should discontinue proton pump inhibitors (PPI) and antibiotic such as amoxicillin, clarithromycin and quinolone groups to ensure that any remaining organisms can repopulate the stomach [4].

#### **b.** Invasive tests

Invasive testing which requires endoscopy should be limited to patients who require endos‐ copy for diagnostic or therapeutic evaluation. Invasive tests available in clinical practice include: gastric biopsies for culture (fig. 2A), gram stain (fig. 2B), histology (fig. 3A), or rapid urease testing (fig. 3B). Rapid urease test such as CLO test plus upper GI endoscopy usually cost between 276-502 (average 389) US dollars*. H pylori* culture is the absolute gold standard to diagnose *H. pylori* but culture generally is not available in most hospitals. Good quality laboratories are capable to culture *H. pylori* from gastric biopsies in more than 80% of instances and also offer susceptibility testing such as E-test.

**Figure 3.** A.) *H pylori* detected by histology; (B.) *H pylori* detected by rapid urease test

three mains methods of commercial kits are ELISA (\$90–\$95/correct diagnosis),, immunochro‐

Most serologic tests carries a high sensitivity (~90 to 100%), but variable specificity (under 85-90%). Their positive and negative predicative values depend upon the background prevalence of *H. pylori* infection in the population at risk. In areas where infection is common, a negative test is likely to be a false negative. Conversely, a positive test amongst those in whom *H pylori* is infrequent is more likely to be a false positive. In developed countries with low prevalence of *H. pylori* infection (<20%), for example, a positive serological test signals active infection only about half the time. Hence, serology should be validated locally. Further, antibody tests can remain positive for years after *H pylori* eradication and have limited value

The urea breath test provides a reliable noninvasive method for *H pylori* detection with sensitivity and specificity of 88-95% and 95%-100% respectively. [33] Urea breath testing is not only sensitive and specific but has an important advantage to confirm *H pylori* eradication. Following ingestion of 13C- or 14C-urea, *H pylori*-produced urease enzyme that is resident in the stomach hydrolyzes this labeled urea to 14CO2 or 13CO2, which can be detected in breath samples [34] (fig. 1). The nonradioactive13C (a stable label) test and the radioactive 14C test have received US Food and Drug Administration (FDA) approval for *H pylori* diagnosis. The dose of radiation in the 14C-urea test however is not approved for use in children and pregnant

*H. pylori* in the stomach also appears in the stool, allowing the development of fecal assays: *H pylori* culture, DNA detected by polymerase chain reaction (PCR), or *H pylori* antigen testing. Only stool antigen has proven to be clinical useful with sensitivities and specificities of more than 90%. Stool antigen assay is advantageous to confirm eradication. To avoid false negative results, it is generally recommended that post-treatment testing with the UBT, histology, stool antigen test or culture be delayed for 4 weeks and the patients should discontinue proton pump inhibitors (PPI) and antibiotic such as amoxicillin, clarithromycin and quinolone groups to

Invasive testing which requires endoscopy should be limited to patients who require endos‐ copy for diagnostic or therapeutic evaluation. Invasive tests available in clinical practice include: gastric biopsies for culture (fig. 2A), gram stain (fig. 2B), histology (fig. 3A), or rapid urease testing (fig. 3B). Rapid urease test such as CLO test plus upper GI endoscopy usually cost between 276-502 (average 389) US dollars*. H pylori* culture is the absolute gold standard to diagnose *H. pylori* but culture generally is not available in most hospitals. Good quality laboratories are capable to culture *H. pylori* from gastric biopsies in more than 80% of instances

ensure that any remaining organisms can repopulate the stomach [4].

and also offer susceptibility testing such as E-test.

matography, and Western blotting.

60 Dyspepsia - Advances in Understanding and Management

to confirm eradication of *H pylori* infection4.

**2.** Urea breath test (UBT)

**3.** Fecal *H. pylori* detection

women [4].

**b.** Invasive tests

Histological examination has an advantage over other diagnostic tests by providing morpho‐ logical information such as severity of gastritis, and evidence for dysplasia. The accuracy of histological examination however may be variable due to density of *H. pylori* and sampling error, and is dependent upon histopathogical interpretation. The accuracy of histological diagnosis of *H pylori* infection can be improved by adequate biopsies from the antrum and body and by special staining such as a silver staining and the Diff-Quik stain [35].

Rapid urease tests contain a solution or gel with urea and a pH indicator reagent. The presence of urease from *H pylori* results in hydrolysis of neutral urea to alkaline ammonia, which is then visualized by a change in color of the pH indicator. The rapid urease test has a high sensitivity (95%) and specificity (95%), [36] making it an excellent primary diagnostic test.

Any concomitant use of antibiotics or PPI however will reduces bacterial load, and may lead to false negative tests such as rapid urease tests, urea breath test and histology. [4]
