Digestive Diseases and Sciences, Vol. 50, No. 3 (March 2005), pp. 449–452 (C2005) DOI: 10.1007/s10620-005-2456-5
Comparison of the Clinical Feasibility
of Three Rapid Urease Tests in the Diagnosis
of Helicobacter pylori Infection
CHANG-AN TSENG, MD,* WEN-MING WANG, MD,† and DENG-CHYANG WU, MD, PhD†
Rapid urease tests (RUTs) are a fast, accurate, and inexpensive method to diagnose H. pylori infection in the endoscopy suite. Of these, the CLO test is both common and widely used. The aim of our study was to evaluate the accuracy and positive reaction times of two new rapid urease tests (ProntoDry and HpONE) in comparison with the CLO test. Fifty-one patients (26 men, 25 women; mean age, 52.4 years) were included in this study, and all underwent esophagogastroduodenoscopy (EGD). None of the patients had received any prior H. pylori eradication therapy. H. pylori infection status was evaluated by histology, culture,13C–UBT, and RUT. H. pylori infection was considered to be
positive if the culture was positive or if two of the other three tests (histology, RUT, and13C–UBT)
were positive. If culture was negative and only one of the other three tests was positive, or if all four tests were negative, the result was interpreted as negative. Of these 51 patients, 2 were excluded and 29 (59.1%) were infected with H. pylori. The sensitivities, specificities, positive predictive values, and negative predictive values of the three RUTs were not significantly different. The mean positive reaction times of the three RUTs (CLO test, ProntoDry, and HpONE) were 67.8± 12.0, 16.5 ± 2.2, and 17.8± 2.1 min, respectively. ProntoDry (P < 0.001) and HpONE (P < 0.001) had significantly faster reaction times than the CLO test, but there was no significant difference between ProntoDry and HpONE. Different media of RUTs may influence the rapidity of a positive reaction time. Both ProntoDry and HpONE were superior to the CLO test in terms of accuracy, reaction time, and cost-effectiveness.
KEY WORDS: Helicobacter pylori; diagnosis; rapid urease test.
Helicobacter pylori is one of the most common causes of
chronic bacterial infection in humans and has been asso-ciated with gastritis, peptic ulcer, gastric cancer, and other gastrointestinal disorders (1). Many diagnostic methods have been developed to detect H. pylori infection, includ-ing invasive (rapid urease test [RUT], histology, culture,
Manuscript received July 5, 2004; accepted September 9, 2004. From the *Division of Gastroenterology, Department of Internal Medicine, Buddhist Tzu Chi General Hospital, Dalin, Chia-Yi, and †Division of Gastroenterology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung city, Taiwan.
Address for reprint requests: Dr. Deng-Chyang Wu, Division of Gastroenterology, Department of Internal Medicine, Kaohsiung Medical University Hospital, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan; [email protected].
and polymerase chain reaction) and noninvasive (serology, urea breath test [UBT], and, more recently, H. pylori anti-gen determination on feces) (2–6). The current concepts (as seen in the Maastricht 2-2000 Consensus Report) in the management of H. pylori infection recommend a “test and treat” approach (7). Consequently, rapid and accurate diagnostic methods are necessary for patients to receive appropriate therapy immediately after endoscopy.
Endoscopy is an important tool for primary diagnosis in dyspeptic patients, and biopsy-based tests are appropriate for H. pylori detection. However, in biopsy-based tests, the accuracy of histological tests depends to a large degree on the expertise of the pathologist, while the accuracy of cultures depends on the conditions in which the specimens
Digestive Diseases and Sciences, Vol. 50, No. 3 (March 2005)
449
TSENG ET AL. are transported and processed, and obtaining the results of
both culture and histology is time-consuming. In contrast, RUT is a simple, inexpensive, rapid, and reliable method for detecting urease activity in gastric specimens and is considered by clinicians to be the initial test of choice for diagnosis of H. pylori.
The CLO test (Delta West Bentley, WA, Australia), an agar gel test, is the most widely used and best-studied RUT, but the reading time of up to 6 hr does not satisfy the criterion of “rapidity.” Two new modified RUT kits are now commercially available with different test media: a dry filter-paper test, ProntoDry (Medical Instruments Corp., Solothurn, Switzerland); and a liquid test, HpONE (GI Supply, Camp Hill, PA).
Our present prospective study compares the clinical ap-plication of these three RUTs (CLO test, ProntoDry, and HpONE).
MATERIALS AND METHODS Patients
Between October 2002 and December 2002, 51 consecutive patients (26 men and 25 women; mean age, 52.4 years; range, 30–72 years) were enrolled in the study. All patients received upper GI endoscopy at Kaohsiung Medical University Hospital. Five sets of biopsies were obtained: two sets of biopsies (each containing one specimen from the lesser curvature side of the antrum and another from the greater curvature side of the gastric body) for histology and H. pylori culture and the other three sets (each containing two antral specimens) for the three different RUTs. All patients also received13C-UBT. The exclusion
cri-teria were as follows: use of proton pump inhibitor, antibiotics, or bismuth within the previous 1 month, prior anti-H. pylori treatment, presence of a bleeding peptic ulcer, previous gastric surgery, chronic use of immunosuppressant drugs or corticos-teroids, and pregnancy or lactation.
Diagnostic Tests for H. pylori Infection
Histological Examination. One set of biopsy specimens was
fixed with formalin, embedded in paraffin, and stained with hematoxylin and eosin. The result of H&E stain was considered to be positive if the characteristic spiral organism was visible under the microscope.
Culture. One set of biopsy specimens was rubbed on the
sur-face of a Campy-BAP agar plate (Brucella agar [Difco]+ Iso-Vitalex [Gibco]+ 10% whole sheep blood) and then incubated at 35◦C under microaerobic conditions (5% O2, 10% CO2, and
85% N2) for 4–5 days. The culture of H. pylori was considered
positive if one or more colonies of gram-negative, oxidase(+), catalase(+), and urease(+) spiral or curved rods were present.
13C-UBT. The13C-urea was 50 mg 99%13C-labeled urea
produced by the Institute of Nuclear Energy Research (INER), Taiwan. One hundred milliliters of fresh milk was used as the test meal. This procedure was modified from our previous study (8). All samples were sent to INER, where a continuous-flow isotope ratio mass spectrometer (CF-IRMS) (Europa Scientific Ltd, Crewe, UK) was used for analysis.
Values are expressed as excessδ13CO
2excretion per mil units.
Theδ13CO
2is the ratio of13C to12C in the sample, compared
with that in the PDB standard, and is expressed by the following equation:δ13CO
2= (Rsamp− Rstd)/Rstd× 1000. Rsampand Rstd
represent the ratios of13C to12C in the test and baseline samples,
respectively. Excessδ13CO
2is the value ofδ13CO2detected at
15 min minus that at baseline. According to our previous study, the cutoff value was 3.5 per mil at 15 min after taking13C-urea.
A value greater than or equal to 3.5 per mil was interpreted as indicating a H. pylori-positive status.
Rapid Urease Test. The results of CLO test (Delta West
Bentley) were interpreted as positive if the color of the gel changed from yellow to pink or red within 24 hr at room tem-perature. The results of ProntoDry (Medical Instruments Corp., Solothurn, Switzerland) were considered to be positive if an ex-panding pink-color external ring was noted around the biopsy specimens. The results of HpONE (GI Supply, Camp Hill, PA) were considered to be positive if the color of the reagent changed to a light-blue or blue color. The reaction time was recorded in minutes. The final reading of ProntoDry and HpONE, as rec-ommended by the manufacturer, was 1 hr. Results of the urease tests were read every 5 min until positive or at 1 hr for Pron-toDry and HpONE and for up to 24 hr for CLO test by the same technician.
Confirmation of H. pylori Infection
H. pylori infection was considered to be positive when the
culture was positive or two of the other three tests (histology, RUT, or13C-UBT) were positive. Patients with negative results
on all four tests (culture, RUT,13C-UBT, and histology), or a
positive result on only one of the three tests (histology, RUT, and13C-UBT), were assessed as noninfected.
Statistical Analysis
Chi-square test and Fisher’s exact test were used for statistical analysis.
RESULTS
Among the 51 patients, endoscopic diagnosis revealed gastric ulcer (n= 8), duodenal ulcer (n = 33), gastritis (n= 3), gastroduodenal ulcer (n = 4), and others (n = 3; 1 leiomyoma, 1 gastric polyp, and 1 gastric cancer). Two patients (one duodenal ulcer and one gastric ulcer) were excluded because of their having taken PPI within 1 month of endoscopic examination. Twenty-nine patients (59.1%) were H. pylori positive and 20 patients (40.9%) were
H. pylori negative. The sensitivity, specificity, positive
predictive value (PPV), negative predictive value (NPV), mean positive reaction time (PRT), and median posi-tive reaction time of the three different RUTs (CLO test, ProntoDry, and HpONE) are shown in Table 1. The data revealed that the three RUTs (CLO test, ProntoDry, and HpONE) had similar specificities (100, 100, and 100%) and PPVs (100, 100, and 100%). However, the ProntoDry test and the HpONE had greater sensitivity (93 and 93%) and NPVs (90.3 and 90.3%) than the CLO test (sensitiv-ity; 86%; NPV, 83.3%). In addition, the ProntoDry test
CLINICAL FEASIBILITY OF THREE RUT TESTS
TABLE1. VALIDITY OFTHREECOMMERCIALLYAVAILABLERAPIDUREASETESTS
Sensitivity Specificity PPV NPV Mean PRT Median PRT
(%) (%) (%) (%) (min) (min) Price
CLO test 86.2 100 100 83.3 67.8± 12*† 46 $4.41
ProntoDry 93 100 100 90.3 16.5± 2.2* 15 $2.94
HpONE 93 100 100 90.3 17.8± 2.1† 15 $3.52
Note. PPV, positive predictive value; NPV, negative predictive value; PRT, positive reaction time.
*P< 0.001, †P < 0.001.
(P < 0.001) and the HpONE test (P < 0.001) had sig-nificantly faster mean PRTs than the CLO test (16.5± 2.2, 17.8± 2.1, and 67.8 ± 12.0 min, respectively), but there was no significant difference between the ProntoDry test and the HpONE test. As indicated in Figure 1, 50% of
H. pylori–positive patients showed positive results in both
ProntoDry and HpONE tests within 15 min, and more than 90% showed positive results within 30 min. On the other hand, the CLO test required much more time (>167 min) to yield the same percentage (90%).
DISCUSSION
The RUT is based on the ability of H. pylori to pro-duce urease, which is not usually present in the stomach. Urease produced by the organism converts urea to ammo-nia, resulting in a rise in pH values and a change in the color of the medium. RUTs are quite useful for diagnosing
H. pylori, with the advantage of providing quick and
reli-able results after endoscopy. In addition, RUTs are inex-pensive and can easily be performed in a local laboratory. This is in contrast to the time required to obtain the re-sults of culture and histology, which is usually several days. The rapid diagnostic ability of RUTs enables clini-cians to initiate therapy for patients immediately and re-duces medical expenses incurred by repeat visits to the clinic. RUTs may also improve the success rate of H.
pylori eradication, because patient compliance is
consid-Fig 1. Comparison of the H. positive percentage rates in H. pylori-infected patients at different reaction times among the three different rapid urease tests.
ered to play an important role in the successful treat-ment of H. pylori, and early diagnosis may improve compliance (9).
The first commercial RUT was the CLO test, which was made into an agar gel form with urea, phenol red, and buffers in a sealed plastic slide. The medium’s color change to dark pink or magenta was interpreted as a posi-tive result. In our study, the CLO test had a specificity and positive predictive value of 100%. Although some previ-ous data showed that sensitivities of CLO test were in the range of 90–99% (10–12), the sensitivity of the CLO test in our study was 86.2%. The ProntoDry test consists of a dry filter paper containing urea, phenol red, buffers, and a bacteriostatic agent in a sealed plastic slide and has the advantage that, unlike the other two tests, it need not be re-frigerated. HpONE consists of a liquid reagent containing urea. The appearance of any blue color, even a light blue, of the reagent is considered positive. This may reduce the number of misinterpretations caused by specimens con-taminated with blood. Both ProntoDry and HpONE had greater sensitivity and negative predictive values (NPVs) than CLO test.
In this study, the mean PRT of CLO test was 67.8± 12.0 min, which is similar to findings of previous reports (11). ProntoDry and HpONE had significantly faster mean PRTs than the CLO test. Many published data have re-ported that the urease testing process (jumbo vs. ordi-nary forceps and warmed vs. room temperature), location (antrum vs. body), and number of specimens might influ-ence the results of RUTs (13–17). Because the specimens were taken from the antrum and side by side, the use of different kinds of media may explain the better results of ProntoDry and HpONE than the CLO test, in that the diffusion of urea in agar gel medium is slower.
In conclusion, the two new RUTs (ProntoDry and HpONE) show greater accuracy and shorter reaction times than the CLO test. Both are superior to the CLO test and may be more suitable for clinical practice.
ACKNOWLEDGMENTS
This work was supported by a grant from the National Science Council of the ROC (NSC-90-2314-B-037-104). The authors
TSENG ET AL. thank the Statistics Unit of the Department of Clinical Research
at KMUH for its support and assistance.
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