Validity and cost comparison of ¹⁴carbon urea breath test for diagnosis of H Pylori in dyspeptic patients

Abstract

AIM: To validate and compare the cost of microdose ¹⁴C urea breath test (UBT) with histology and rapid urease test for the diagnosis of H Pylori.

METHODS: Ninety-four consecutive patients with dyspeptic symptoms undergoing gastroscopy were enrolled. Gastric biopsies were taken for histology and rapid urease test. UBT was performed after gastroscopy by microdose ¹⁴C urea capsules. Sensitivity, specificity and accuracy of UBT were calculated and compared with histology and rapid urease test. Cost comparison of these tests was also performed.

RESULTS: H pylori was diagnosed by histology and rapid urease test in 66 (70%) and 61 (65%) patients, while ¹⁴C UBT detected infection in 63 (67%). Accuracy of UBT was 93% in comparison with histology while its positive and negative predictive values were 97% and 84%, respectively. Comparison of ¹⁴C UBT with rapid urease test gives an accuracy of 96%, with positive and negative predictive values of 95% and 97%, respectively. These results were highly reproducible with a Kappa test (P value < 0.001). Cost of histology or rapid urease test with gastroscopy was 110 USD or 95 USD respectively while the cost of UBT was 15 USD.

CONCLUSION: Microdose ¹⁴C UBT was comparable to histology and rapid urease test. ¹⁴C UBT is an economical, self sufficient and suitable test to diagnose active H pylori infection in less developed countries.

INTRODUCTION

H Pylori is a gram negative, microaerophilic human pathogen which is prevalent worldwide. H Pylori infection causes gastritis and is associated with development of peptic ulcer disease, gastric carcinoma, lymphoma, micronutrient deficiencies and ischemic heart disease[1,2]. The International Agency for Research on Cancer classified H Pylori as group 1 carcinogen (a definite cause of cancer in humans)[3].

H Pylori can be diagnosed by invasive techniques requiring endoscopy and biopsy such as histology, tissue culture and detection of H Pylori by polymerase chain reaction. The non-invasive techniques for the diagnosis of H Pylori include serum H Pylori antibody titer, urea breath test (UBT) and H Pylori stool antigen test. A reliable, non-invasive and economical diagnosis is a best choice for the management of H Pylori in both test and treatment.

Among the non-invasive tests, UBT is supposed to be a gold standard test for the diagnosis of H Pylori infection. UBT is based on enzymatic hydrolysis of labeled urea in the stomach by urease, an enzyme produced in abundance by H Pylori. In the presence of H Pylori infection, urea is hydrolyzed to ammonia and carbon dioxide (CO₂). This labeled CO₂ is exhaled and measured for radioactivity. Bacteria other than H Pylori that produce urease in a small amount cannot survive in the gastric mucosa.

There are two types of UBT, ¹³C UBT and ¹⁴C UBT. The former is difficult to analyze because it requires sophisticated infrastructure such as a mass spectrometer, technical expertise and therefore costly while ¹⁴C UBT is an easily available technique that uses ¹⁴C urea capsules with a 5, 3 or 1 uCi dose. The microdose 1 uCi (Helicap) utilizes a very low dose of radiation[4,5]. Considering these facts, in 1997 the Nuclear Regulatory Commission permitted in vivo diagnostic use of capsules containing 1 uCi of ¹⁴C urea without a license[6]. The equipment is small, portable and can be placed on a desktop. Microdose ¹⁴C UBT is claimed to be a reliable and economical diagnostic test for H Pylori infection, which may be used even in remote areas with limited resources.

This prospective study was done to determine the validity and cost of microdose ¹⁴C UBT in comparison with histology and rapid urease test for the diagnosis of H Pylori.

MATERIALS AND METHODS

All consecutive men and non-pregnant women with dyspeptic symptoms undergoing gastroscopy were considered for enrollment.

Dyspepsia was defined as the presence of one or more of the postprandial fullness, early satiation, or epigastric pain or burning for the last three months with symptom onset at least six months before diagnosis according to the latest Rome III criteria[7].

Inclusion criteria

Patients of both genders with dyspepsia were 18-70 years in age. Patients with a history of recent intake of proton pump inhibitor and antibiotics were enrolled only if four weeks have passed since last systemic antibacterial or bismuth medication therapy and 1 wk since last use of proton pump inhibitor or H2-receptor antagonist.

Exclusion criteria

Pregnant women, patients who had gastric surgery, patients with a history of H Pylori eradication therapy in the past six months and patients with active gastrointestinal bleeding were excluded from the study.

Ethical clearance

Study protocol was approved by the institutional ethical review committee. Written informed consent was obtained from all patients before enrollment.

Endoscopy and biopsy sampling

After overnight fast, esophago-gastro-duodenoscopy was performed with Olympus or Pentax videoscope. Six biopsies were taken, three from antrum and other three from the body of stomach from each patient. Two biopsies, one from the antrum and the other from the body were used for rapid urease test and the other four (two from antrum and two from body) for histology.

Rapid urease test

Rapid urease test kit (Pronto Dry, Medical Instrument Corp., France) was used to detect the presence of H Pylori urease[8]. Result was read in 30 min and 1 h after sampling. The color change from yellow to pink was considered positive and no color change as a negative result. Results were interpreted by either endoscopist or his assistant who were blinded about the results of UBT and histology.

Histology

Four biopsy specimens (two from corpus and two from antrum) were processed separately for histological examination according to standard procedure. Hematoxylin and eosin (HE) and Giemsa staining was performed on these samples. Results were interpreted by a pathologist who was blinded about the results of UBT and rapid urease test. Pathologist commented on the active and chronic H Pylori infection based on the presence of H Pylori along with neutrophils, eosinophils, lymphocytes, lymphoid follicles, and intestinal metaplasia according to the classification by Genta RM et al[9].

¹⁴C UBT

Patients swallowed 37 kBq (1 uCi) of an encapsulated form of ¹⁴C-urea/citric acid composition (Helicap, Noster System AB Stockholm, Sweden) with water after endoscopy. Breath samples were collected with a special dry cartridge system (Heliprobe Breath Card, Noster System AB Stockholm, Sweden) after 10 min. Patients exhaled gently into the cartridge mouthpiece until the indicator membrane changed in color from orange to yellow. Breath card was inserted into a β-scintillation counter (Heliprobe-analyser, Noster System AB Stockholm, Sweden) and activity was counted for 250 s. This is a portable machine that can be placed on a desktop. Results were expressed both as counts per minute (HCPM) and as grade (0: not infected, CPM < 25; 1: equivocal, CPM 25-50; 2: infected, CPM > 50), which was suggested by the producer according to the counts obtained from the cartridges[10]. Grades 0 and 1 were considered negative for the detection of H Pylori.

Statistical analysis

The statistical package for social science SPSS (release 11.5, standard version, copyright © SPSS) was used for data analysis. The descriptive analysis was done for demographic features. Results were presented as mean ± SD in number (percentage).

Sensitivity, specificity, positive and negative predictive values of UBT with 95% confidence intervals were calculated against histology and rapid urease test. Kappa test was applied to check the reproducibility of the results. Cost comparison of these diagnostic methods was also performed.

RESULTS

Ninety-four consecutive patients with dyspeptic symptoms undergoing gastroscopy were enrolled for the validity of microdose ¹⁴C UBT. There were 60 (64%) men and the mean age of study group was 40.8 ± 12.8 years. H Pylori infection was diagnosed by histology in 66 (70%) patients and by rapid urease test in 61 (65%) patients. UBT detected active H Pylori infection in 63 (67%) patients. Demographic characteristics of the patients and results of these diagnostic tests are summarized in Table 1.

Table 1.

Patient demographics and results of H Pylori detection by various tests (n = 94), mean ± SD

Parameters	n (%)
Gender
Male	60 (64)
Female	34 (36)
Age (yr)	40.8 + 12.8
Histopathology
Positive	66 (70)
Negative	28 (30)
UBT
Positive	63 (67)
Negative	31 (33)
Rapid urease test
Positive	61 (65)
Negative	33 (35)

¹⁴C UBT vs histology

In comparison with histology, UBT has a sensitivity and specificity of 92% (95% CI: 87%-95%) and 93% (95% CI: 79%-99%), respectively. The positive predictive value (PPV) of ¹⁴C UBT was found to be 97% (95% CI: 91%-99%) and negative predictive value (NPV) was 84% (95% CI: 72%-89%) compared with histology. These results show that UBT has an accuracy of 93% as compared with histology. Kappa test result was 0.805 with P value < 0.001, indicating that these results were reproducible (Table 2).

Table 2.

Sensitivity and specificity of ¹⁴C UBT against histopathology and rapid urease test for H Pylori diagnosis (n = 94)

UBT compared to:	Sensitivity (95% CI)	Specificity (95% CI)	PPV (95% CI)	NPV (95% CI)	Accuracy
Histopathology	92% (87-95)	93% (79-99)	97% (91-99)	84% (72-89)	93%
Rapid urease test	98% (93-99)	91% (80-94)	95% (89-97)	97% (86-99)	96%

UBT: urea breath test; PPV: positive predictive value; NPV: negative predictive value; CI: confidence interval.

¹⁴C UBT vs rapid urease test

In comparison of UBT and rapid urease test, the sensitivity and specificity of UBT were 98% (95% CI: 93%-99%) and 91% (95% CI: 80%-94%). The PPV and NPV were 95% (95% CI: 89%-97%) and 97% (95% CI: 86%-99%), respectively. UBT has an accuracy of 96% in comparison with rapid urease test. Result of Kappa test was 0.881 (P ≤ 0.001) which showed a good response (Table 2).

Four patients with histological evidence of H Pylori infection had negative results with UBT and rapid urease test. The discordant results between histology, UBT and rapid urease test are shown in Table 3.

Table 3.

Discordant results between histopathology, ¹⁴C UBT and rapid urease test for H Pylori diagnosis (n = 94)

Groups	Patients (n)	Histopathology	UBT	RUT
Group 1	59	+	+	+
	2	+	+	-
	1	+	-	+
	4	+	-	-
Group 2	1	-	+	+
	1	-	+	-
	26	-	-	-

UBT: urea breath test; RUT: rapid urease test; +: positive; -: negative.

Cost analysis

At the time of this study, the cost of gastroscopy was 90 USD while the cost of histology and rapid urease test was 20 USD and 5 USD in our institute. Therefore, the overall cost of H Pylori diagnosis by histology was 110 USD and 95 USD by rapid urease test. The cost of UBT was only 15 USD in our institute.

DISCUSSION

Current guidelines for the management of H Pylori infection recommend eradication treatment without performing endoscopy in patients under 45 years of age who have no remarkable symptoms[11-13]. The use of non-invasive tests has been advocated in different strategies for management of dyspeptic patients in the primary care based on clinical and economical analyses[14,15].

Invasive diagnostic tests for H Pylori diagnosis need gastroscopy that requires sedation and monitoring during the procedure by trained staff and expertise. These diagnostic tests are costly and require an established healthcare infrastructure.

In practical terms, invasive tests for the diagnosis of H Pylori are not feasible, especially in less developed countries. An economical, reliable and office based diagnostic test is therefore, more appropriate in settings of under privileged and cost constraint societies.

Other factors that determine choice of diagnostic tests apart from accuracy, in primary care setting include the availability of test, ease to perform, cost, self-sufficiency and acceptance by the patients. Present study has shown that microdose ¹⁴C UBT has all these features.

Our study has demonstrated a high accuracy of microdose ¹⁴C UBT for the detection of H Pylori infection comparable to histological diagnosis of H Pylori. The results of present study are comparable to other studies, with a sensitivity and specificity of more than 90% for the diagnosis of H pylori infection[16-18].

The sensitivity and specificity of ¹⁴C UBT were 98% and 91% while PPV and NVP were 95% and 97% respectively, compared with rapid urease test. The overall accuracy was 96%. These results are similar to another study that found a 93% sensitivity, 96% specificity and 95% accuracy in comparison with rapid urease test[19]. Moreover, studies using a combination of histopathology and rapid urease test as a gold standard has also reported a comparable sensitivity and specificity of ¹⁴C UBT above 90%[20,21].

H Pylori Stool Antigen (HpSA) test is a promising non-invasive test. This test seems to be equivalent to the UBT in terms of its yield of diagnosing H Pylori[22]. However, collection of stools may be a disagreeable task for many patients and it is difficult to manage in office based settings. H Pylori serum antibody test is another non-invasive test. It has a low sensitivity and specificity and it does not indicate active H Pylori infection because antibody titers can remain high for a long period despite adequate treatment[23]. It is one of the best tests for estimation of sero-prevalence of H Pylori, unfortunately it is not an ideal test for the diagnosis of active H Pylori infection.

It has been shown that UBT becomes false negative during treatment with proton pump inhibitors and H-2 blockers[24,25]. However, it has been observed recently that addition of citric acid in the urea capsule may diminish the negative effect of acid inhibitory drugs on the accuracy of ¹⁴C UBT[26]. Although we used an acidified ¹⁴C urea capsule (Helicap), we preferred to discontinue anti-acid medications for at least seven days before the test. Controversies exist regarding the best diagnostic test for H Pylori among patients with active upper GI bleeding. ¹³C UBT was found better than histology and rapid urease test by a few studies in patients with active upper GI bleeding[27,28]. However, validity of ¹⁴C UBT in patients with active upper GI bleeding has never been assessed.

Concerns about the radiation hazard can be raised against ¹⁴C UBT. However, it has been found in practice that by using microdose ¹⁴C UBT, only a small amount of isotope was used and the test actually entailed low radiation exposure (3 mSv)[29,30].

Nearly the entire ingested isotope is rapidly excreted in urine or breath within 72 h. Recently safety of microdose ¹⁴C UBT has been established even in young children[31].

In conclusion, microdose ¹⁴C UBT is a highly sensitive and specific non-invasive test comparable to the invasive methods such as histology and rapid urease test used for H Pylori diagnosis. This test requires no sophisticated infrastructure. ¹⁴C UBT is self-sufficient and easy to perform with readily available results. In our opinion, this is one of the best options for detection of H Pylori infection in office based settings, especially in less developed countries.

ACKNOWLEDGMENTS

The authors want to thank Mr. Mohammad Islam for his statistical advice and Ms. Rozina Wasaya for her support in endoscopy.

COMMENTS

Background

H pylori is one of the most prevalent infection organisms, especially in low socio-economic societies. It is associated with intestinal and extra-intestinal manifestations including malignancy. There is a need to establish cost-effective eradication strategies especially in less developed countries.

Research frontiers

Microdose ¹⁴C Urea Breath Test (UBT) is carried out without the use of sophisticated equipment and specialized trained personnel. There is a need to compare the diagnostic usefulness of ¹⁴C UBT with other diagnostic modalities such as histopathology and rapid urease test for H pylori detection. This comparison will help establish the value of ¹⁴C UBT in resource constraint settings.

Innovations and breakthrough

¹⁴C UBT is not a commonly used diagnostic method and there are only few studies about the accuracy of ¹⁴C UBT for H pylori diagnosis. This study concluded that the sensitivity and specificity of microdose ¹⁴C UBT is comparable to mostly used invasive diagnostic tests, such as histopathology and rapid urease test.

Application

Microdose ¹⁴C UBT may be utilized for the non-invasive diagnosis of H pylori especially in the areas lacking an established health care structure. It can be used in accordance with the “test and treatment” policy in patients with dyspepsia without remarkable features.

Terminology

Dyspepsia is defined as the presence of one or more symptoms of the postprandial fullness, early satiation, epigastric pain or burning for the past three months with symptom onset at least six months before the diagnosis according to the latest Rome III criteria. ¹⁴C UBT is available in 5, 3 and 1 uCi dose. The microdose 1 uCi (Helicap) utilizes a very low dose of radiation.

Peer review

This is an interesting paper which addresses an important issue in the diagnosis of H pylori infection. Authors reported that the microdose ¹⁴C UBT is a simple, less expensive and accurate test to diagnose H pylori infection. The paper is well written and conclusions are supported by results.