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A prospective comparison of locally made rapid urease test and histology for the diagnosis of Helicobacter pylori infection
A prospective comparison of locally made rapid urease test and histology for the diagnosis of Helicobacter pylori infection Kent-Man Chu, MB, BS, FRCS(Ed), Ronnie Poon, MB, BS, FRCS(Ed), Henry H. Tuen, MB, BS Simon Y. K. Law, MB, BCh, FRCS(Ed), Frank J. Branicki, DM, FRCS, FRACS John Wong, PhD, FRCS(Ed), FRACS, FACS Hong Kong, China
Background: A number of noncommercial preparations of urease test have been described. The present prospective study evaluated the accuracy of one such preparation for the diagnosis of Helicobacter pylori infection. Methods: From February 1996 to November 1996, all patients undergoing elective upper endoscopy in a single endoscopy facility were included. Three antral biopsy specimens were taken. Two specimens were subjected to histologic examination, and one specimen was placed into a "locally made rapid urease test" (LRUT). Results of histologic examinations were taken as standards for comparison. The final result of LRUT was obtained on scrutiny of color changes at 4 hours after the start of the test. Results: Two thousand three hundred sixteen patients (male/female = 1.5:1) with a mean age of 56.7 -+ 0.4 years were included. Five hundred sixty-two patients (24.3%) had a history of eradication treatment for H. pylori. Nine hundred fifty-three patients (41.1 %) were found to be positive for H. pylori on histologic examination. In patients in whom a history of eradication therapy was absent, the sensitivity, specificity, and positive and negative predictive values of the LRUT were 92.8%, 97.6%, 97.5%, and 93.0%, respectively. In patients with a history of eradication treatment, the corresponding figures were 76.1%, 99.6%, 96.2%, and 96.9%. Conclusions: The locally made rapid urease test provides a simple, safe, rapid, inexpensive, and accurate test for the diagnosis of H. pylori infection. (Gastrointest Endosc 1997;46:503-6.)
It is well accepted that antibiotic treatment is indicated for all patients with Helicobacter pylori infection and peptic ulcer disease. 1 Although a variety of techniques are available for the diagnosis of H. pylori infection, 2 an ideal test needs to be simple, safe, rapid, inexpensive, accurate, and readily available for clinical application. Among patients having diagnostic upper endoscoReceived February 25, 1997. For revision May 13, 1997. Accepted July 30, 1997. From the Division of Upper Gastrointestinal Surgery, Department of Surgery, The University of Hong Kong, Queen Mary Hospital, Hong Kong, China. Reprint requests: Kent-Man Chu, MB, BS, FRCS(Ed), Department of Surgery, The University of Hong Kong, Queen Mary Hospital, Pokfulam Rd., Hong Kong, China. Copyright © 1997 by the American Society for Gastrointestinal Endoscopy 0016-5107/97/$5.00 + 0 37/1/85052 VOLUME 46~ NO. 6, 1997
py, urease testing of gastric mucosal biopsy specimens is the initial test of choice. Urease testing involves a preparation containing urea and a pH sensitive marker. In the presence of urease produced by H. pylori, urea will be converted to ammonia with a resultant change in pH and color. There are several commercial kits available for rapid urease testing. 3 These kits are considered to be relatively inexpensive when compared with histologic and culture studies. 2 However, their cumulative cost will be substantial if a large number of tests are performed. A number of locally made, noncommercial preparations which are considerably cheaper than the commercial kits have been described in the literature.< 5 The present prospective study evaluated the accuracy of one such preparation in a comparison with histologic analysis for the diagnosis of H. pylori infection. GASTROINTESTINAL ENDOSCOPY 503
K-M Chu, R Poon, H Tuen, et al.
Locally made rapid urease test and histology for diagnosis of H. pylori
Table 1. Indications for upper endoscopy in 2316 patients Indications
No. of patients (%)
Epigastric pain History of duodenal ulcer History of gastric ulcer History of gastritis History of gastrointestinal bleeding History of duodenitis History of perforated peptic ulcer History of pyloric stenosis Dysphagia History of stomal ulcer
1326 (57.3) 399 (17.2) 198 (8.5) 155 (6.7) 125 (5.4) 51 (2.2) 43 (1.9) 8 (0.3) 6 (0.3) 5 (0.2)
PATIENTS AND METHODS From February 1996 to November 1996, all patients undergoing elective upper endoscopy by members of the Division of Upper Gastrointestinal Surgery at our hospital were eligible for this study. Patients were excluded if they (1) were receiving a proton pump inhibitor or (2) within the past 6 weeks had received bismuth compounds, antibiotics, or eradication therapy for H. pylori. Patients who had received eradication therapy for H. pylori more than 6 weeks earlier were not excluded. Patients were consecutively enrolled and fasted for at least 8 hours before endoscopic examination. Endoscopic examination was performed under local pharyngeal anesthesia (Cetacaine spray; Cetylite Industries, Pennsauken, N.J.) with the patient lying in a left lateral position. Regardless of the endoscopic findings, three antral mucosal biopsy specimens were taken from within 3 cm of the pylorus and removed from the biopsy forceps (Olympus FB 25K; Olympus, Tokyo, Japan) with a needle. Two biopsy specimens were fixed with 10% formalin for histologic examination under hematoxylin and eosin stain with the result of the rapid urease test being unknown to the pathologist. Giemsa staining was done at the discretion of the pathologist. The presence ofH. pylori was established by its typical appearance on scanning along the mucosal surface and the individual gastric pits. A low density of/-/. pylori on histologic examination was defined as the identification of individual organisms, or small groups, covering less than one third of the gastric mucosal surface. 6 The remaining biopsy specimen was placed immediately, in the endoscopy unit, into a capped tube containing 1 ml of freshly prepared 5% (wt/vol) unbuffered urea in distilled water including two drops of 1% phenol red. The tube was placed in a rack at room temperature and was examined at 1 hour and 4 hours. The tube was labeled with the patient's name and identification number only. A single observer without knowledge of the patient's history and diagnosis read the test. A color change from yellow to pink in this "locally made rapid urease test" (LRUT) was recorded as a positive test. For the last 100 positive LRUTs, the time for color change was measured to the nearest minute. Continuous values were expressed as mean +_ standard error of the mean. Results of histologic examination were 504 GASTROINTESTINAL ENDOSCOPY
Table 2. Endoscopic findings in 2316 patients
Endoscopic findings
No. of patients with eradication therapy
Total No. of patients (%)
Normal Gastritis Duodenal ulcer Gastric ulcer Duodenitis Reflux esophagitis Carcinoma of stomach Stomal ulcer Gastric polyp
542 3 9 5 2 0 0 0 1
1238 (53.4) 337 (14,6) 310 (13.4) 212 (9.2) 135 (5.8) 30 (1.3) 28 (1.2) 16 (0.7) 10 (0.4)
Total
562 (24.3%)
2316 (100)
taken as the standard for comparison. The final result of the LRUT was judged at 4 hours. The sensitivity, specificity, and positive and negative predictive values of the LRUT were determined. The prevalence ofH. pylori infection in Hong Kong was previously reported to be about 55%. 7
RESULTS T h e r e w e r e 2316 p a t i e n t s w i t h a m e a n age of 56.7 _+ 0.4 y e a r s . T h e r e w a s a m a l e p r e p o n d e r a n c e ( m a l e / f e m a l e = 1.5:1). F i v e h u n d r e d sixty-two pat i e n t s (24.3%) h a d a h i s t o r y of e r a d i c a t i o n t h e r a p y for H. pylori. I n d i c a t i o n s for u p p e r e n d o s c o p y a r e s h o w n in T a b l e 1. T h e s e p a t i e n t s h a d u p p e r g a s t r o i n t e s t i n a l s y m p t o m s , k n o w n peptic u l c e r d i s e a s e s w i t h r e c u r r e n t s y m p t o m s or a f t e r t r e a t m e n t , or r e c e n t h i s t o r y of c o m p l i c a t e d peptic ulcer diseases. F i n d i n g s a t u p p e r e n d o s c o p y a r e s h o w n in T a b l e 2. N i n e h u n d r e d fifty-three p a t i e n t s (41.1%) w e r e f o u n d to h a v e b i o p s y s p e c i m e n s positive for H. pylori on histologic e x a m i n a t i o n . T h e d e n s i t y of H. pylori w a s c o n s i d e r e d to be low on histologic e v a l u a t i o n in 73 p a t i e n t s , s e v e n of w h o m h a d received e r a d i c a t i o n t h e r a p y for H. priori (p = N o t significant) (Table 3). T h e r e s u l t s of L R U T as c o m p a r e d w i t h histologic e v a l u a t i o n for H. pylori a r e d o c u m e n t e d in T a b l e 3. It is n o t e w o r t h y t h a t 63.8% (51 of 80) of falsen e g a t i v e t e s t s a t 4 h o u r s w e r e r e l a t e d to a low d e n s i t y of H. pylori. T h e sensitivity, specificity, a n d positive a n d n e g a t i v e p r e d i c t i v e v a l u e s of L R U T are s e e n in T a b l e 4. T h e s e n s i t i v i t y of t h e L R U T w a s l o w e r in p a t i e n t s w h o h a d r e c e i v e d e r a d i c a t i o n t h e r a p y for H. pylori. I n t h e l a s t 100 positive L R U T s , t h e m e d i a n t i m e for color c h a n g e w a s 8.0 m i n u t e s ( r a n g e 1 to 120 m i n u t e s ) . T w e n t y - t h r e e p e r c e n t of t e s t s w e r e positive w i t h i n 1 m i n u t e , w h e r e a s 90% of t e s t s w e r e positive b y 25 m i n u t e s .
VOLUME 46, NO. 6, 1997
Locally made rapid urease test and histology for diagnosis of H. pylori
Table 3. Results of locally made rapid urease testing at 4 hours in comparison with histologic examination Histology negative
Histology positive
Histology scanty positive
Total
Urease test negative Urease test positive
1340(493)
29 (9)
51 (7)
1420
23 (2)
851 (51)
22 (0)
896
Total
1363
880
73
K-M Chu, R Poon, H Tuen, et al.
Table 4. Sensitivity, specificity, and positive and negative predictive values of the locally made rapid urease test Sensitivity Specificity PPV NPV Overall Without previous eradication With eradication
(%)
(%)
(%) (%)
91.6 92.8 76.1
98.3 97.6 99.6
97.4 94.4 97.5 93.0 96.2 96.9
PPV, Positive predictive value; NPV, negative predictive value. 2316
Values in parentheses show history of eradication ofH. pylori.
DISCUSSION Although several noninvasive and invasive tests are available for the diagnosis ofH. pylori infection, histologic examination of biopsy specimens remains the gold standard. 2' s Histologic examination, however, is expensive and labor intensive, and the result is not usually available on the same day. It is highly desirable and cost effective for outpatients to have their result of H. pylori status during the same endoscopy visit so that they do not have to return again for the prescription of appropriate treatment. On the other hand, it is also desirable for inpatients, especially those with peptic ulcer hemorrhage, to have H. pylori status determined and appropriate t r e a t m e n t initiated as soon as possible. Rapid urease testing of gastric biopsy specimens is considered to be the initial test of choice in patients undergoing endoscopy because of its low cost, rapid availability of results, simplicity, and accuracy. 2, 3, 9 It was previously believed that urease was a normal component of gastric mucosal biochemistry. 1° After the first report by Langenberg et al. 11 of the production of urease by H. pylori, this property has formed the basis of several diagnostic tests for H. pylori, including urease testing of biopsy specimens and urea breath testing. The first urease test was described by McNulty and Wise in 198512 and used Christensen's 2% urea broth. Subsequently a number of modifications of this test have been reported. 4,5,13,14 The CLOtest (Delta West Ltd., Perth, Australia), which consists of an agar gel containing urea, phenol red, buffers, and a bacteriostatic agent in a sealed plastic slide, was the first urease test to become commercially available. To date, there are several commercial kits marketed for urease testing. 3 All commercial kits have shown good sensitivity (80% to 98%) and specificity (94% to 100%) for the diagnosis ofH. pylori infection. 3, s, 15 Commercial urease test kits cost about $4 to $7 per test. Although considered relatively low cost in comparison with histologic examination or culture of VOLUME 46, NO. 6, 1997
gastric biopsy specimens, 2, 3 cumulative costs will be substantial if numerous tests are performed. In these days of escalating health care costs, it would be prudent to adopt the use of a cheaper alternative if this can be shown to be accurate, and various locally produced rapid urease tests have been described. 4,5'z2-14 The LRUT described in the present study is similar to the one described by Arvind et al., 4 except for a lower concentration of urea in our preparation. The preparation of LRUT does not require special laboratory skills or equipment. It has to be prepared fresh each day, however, to avoid bacterial contamination with organisms such as Proteus or Pseudomonas which may produce a false-positive result with the production of low levels of urease over time. ~ It took nursing staff about 15 minutes daily to prepare the LRUT, and, in our setting, there was no need to pay additional costs for the labor involved. Excluding any labor for preparation, the LRUT costs about $0.01 per test. Assuming that a commercial kit costs $4 per test, in an endoscopy unit performing 5000 tests annually, for example, the estimated savings would be about $19,950 per year. Two biopsy specimens are adequate for an accurate diagnosis of H. pylori infection by histologic examination. 1~ The final result of the LRUT was read at 4 hours because it was considered to be the optimal time acceptable to an endoscopist seeking a same-day result. 3 Although incubation of the test material at 37 ° C shortens the time required for a positive urease test, 17 for simplicity it was not used in the present study; an incubator adds to the cost and complexity of the test. The LRUT was demonstrated to be highly accurate in the present study. In fact, its sensitivity, specificity, and positive and negative predictive values were comparable with those of commercial kits. 3 Although we have regarded the reading at 4 hours as the final result, 90% of tests were positive after 25 minutes. Consequently, the result could be conveyed to the patient during the same endoscopy visit. A correlation has been shown between the density of GASTROINTESTINAL ENDOSCOPY
505
K-M Chu, R Peon, H Tuen, et al.
H. pylori in the biopsy specimens and the time for a positive urease test. 13 This may serve as an explanation for our findings that 63.8% of false-negative tests at 4 hours were related to low density of H. pylori. The false-negative rate may be reduced by monitoring the test for longer than 4 hours. In the present study, however, it would be impractical for our single observer to monitor the test for longer than 4 hours. In the study we included patients who had a history of eradication therapy for H. pylori. This accounted for the relatively high percentage of patients with normal endoscopic findings. The use of a urease test to confirm successful eradication of H. pylori after treatment is not recommended2 The present study showed a lower sensitivity for urease testing in patients with a history of eradication therapy. For patients undergoing repeat endoscopy after eradication treatment, an additional test such as histologic examination should, therefore, be performed to confirm or refute successful eradication of
H. pylori. The present study confirmed the value of the locally produced rapid urease test in clinical practice. Owing to its high accuracy, albeit with occasional false-negative results in patients with low density H. pylori, one can withhold processing of biopsy specimens taken for histologic examination until the result of the urease test becomes available. Such biopsy specimens could then be discarded if the urease test is positive. Alternatively, the biopsy specimens should be examined histologically if the urease test is negative; this is particularly relevant in patients with history of eradication treatment for
H. pylori. REFERENCES 1. NIH Consensus Development Pane] on Helicobacter pylori in peptic ulcer disease. Helicobacter pylori in peptic ulcer disease. JAMA 1994;272:65-9.
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Locally made rapid urease test and histology for diagnosis of H. pylori 2. Brown KE, Peura DA. Diagnosis ofHelicobacter pylori infection. Gastroenterol Clin North Am 1993;22:105-15. 3. Laine L, Lewin D, Naritoku W, Estrada R, Cohen H. Prospective comparison of commercially available rapid urease tests for the diagnosis of Helicobacter pylori. Gastrointest Endosc 1996;44:523-6. 4. Arvind AS, Cook RS, Tabaqchali S, Farthing MJG. Oneminute endoscopy room test for Campylobacter pylori. Lancet 1988;i:704. 5. Katelaris PH, Lowe DG, Norbu P, Farthing MJ. Field evaluation of a rapid, simple and inexpensive urease test for the detection of Helicobacter pylori. J Gastroenterol Hepatol 1992;7:569-71. 6. Price AB. The Sydney system: histological division. J Gastroenterol HepatoI 1991;6:209-22. 7. Ching CK. Yuen ST. Luk ISC. He J. Lain SK. The prevalence of Helicobacter pylori carrmr rates among the healthy blood donors in Hong Kong. J Hong Kong Med Assoc 1994;46:295-8. 8. Yousfi MM, E1-Zimaity HMT, Genta RM. Graham DY. Evaluation of a new reagent strip rapid urease test for detection of Helicobacter pylori infection. Gastrointest Endosc 1996;44: 519-22. 9. Cutler AF. Testing for Helicobacter pylori in clinical practice. Am J Med 1996:100:35S-41S. 10. Glick D. A histochemical study of urease in the human stomach with respect to acid secretion in ulcer and cancer. J Natl Cancer Inst 1949:10:321-30. 11. Langenberg ML, Tytgat GN, Schipper MEI, Rietra PJGM, Zanen HC. Campylobacter-like orgamsms in the stomach of patients and healthy individuals. Lancet 1984;i:1348. 12. McNulty CAM. Wise R. Rapid diagnosis of Campylobacterassociated gastritis. Lancet 1985;i:1443-4. 13. Hazell SL. Borody TJ, Gal A, Lee A. Campylobacterpyloridis gastritis. I. Detection of urease as a marker of bacterial colonization and gastritis. Am J Gastroenterol 1987;82:292-6. 14. Thillainayagam AV. Arvind AS. Cook RS. Harrison [G, Tabaqchali S. Farthing MJ. Diagnostic efficiency of an ultrarapid endoscopy room test for Helicobacter pylori. Gut 1991; 32:467-9. 15. Young EL, Sharma TK. Cutler AF. Prospective evaluation of a new urea-membrane test for the detection of Helicobacter pylori in gastric antral tissue. Gastrointest Endosc 1996:44: 527-31. 16. Thijs JC, van Zwet AA. Thijs WJ, Oey HB, Karrenbeld A~ Stellaard F, et al. Diagnostic tests for Helicobacter pylori: a prospective evaluation of their accuracy, without selecting a single test as the gold standard. Am J Gastroenterol 1996: 91:2125-9. 17. Laine L Estrada R. Lewin DN. Cohen H. The influence of warming of rapid urease test results: a prospective evaluation. Gastrointest Endosc 1996;44:429-32.
VOLUME 46, NO. 6, 1997
Background: A number of noncommercial preparations of urease test have been described. The present prospective study evaluated the accuracy of one such preparation for the diagnosis of Helicobacter pylori infection. Methods: From February 1996 to November 1996, all patients undergoing elective upper endoscopy in a single endoscopy facility were included. Three antral biopsy specimens were taken. Two specimens were subjected to histologic examination, and one specimen was placed into a "locally made rapid urease test" (LRUT). Results of histologic examinations were taken as standards for comparison. The final result of LRUT was obtained on scrutiny of color changes at 4 hours after the start of the test. Results: Two thousand three hundred sixteen patients (male/female = 1.5:1) with a mean age of 56.7 -+ 0.4 years were included. Five hundred sixty-two patients (24.3%) had a history of eradication treatment for H. pylori. Nine hundred fifty-three patients (41.1 %) were found to be positive for H. pylori on histologic examination. In patients in whom a history of eradication therapy was absent, the sensitivity, specificity, and positive and negative predictive values of the LRUT were 92.8%, 97.6%, 97.5%, and 93.0%, respectively. In patients with a history of eradication treatment, the corresponding figures were 76.1%, 99.6%, 96.2%, and 96.9%. Conclusions: The locally made rapid urease test provides a simple, safe, rapid, inexpensive, and accurate test for the diagnosis of H. pylori infection. (Gastrointest Endosc 1997;46:503-6.)
It is well accepted that antibiotic treatment is indicated for all patients with Helicobacter pylori infection and peptic ulcer disease. 1 Although a variety of techniques are available for the diagnosis of H. pylori infection, 2 an ideal test needs to be simple, safe, rapid, inexpensive, accurate, and readily available for clinical application. Among patients having diagnostic upper endoscoReceived February 25, 1997. For revision May 13, 1997. Accepted July 30, 1997. From the Division of Upper Gastrointestinal Surgery, Department of Surgery, The University of Hong Kong, Queen Mary Hospital, Hong Kong, China. Reprint requests: Kent-Man Chu, MB, BS, FRCS(Ed), Department of Surgery, The University of Hong Kong, Queen Mary Hospital, Pokfulam Rd., Hong Kong, China. Copyright © 1997 by the American Society for Gastrointestinal Endoscopy 0016-5107/97/$5.00 + 0 37/1/85052 VOLUME 46~ NO. 6, 1997
py, urease testing of gastric mucosal biopsy specimens is the initial test of choice. Urease testing involves a preparation containing urea and a pH sensitive marker. In the presence of urease produced by H. pylori, urea will be converted to ammonia with a resultant change in pH and color. There are several commercial kits available for rapid urease testing. 3 These kits are considered to be relatively inexpensive when compared with histologic and culture studies. 2 However, their cumulative cost will be substantial if a large number of tests are performed. A number of locally made, noncommercial preparations which are considerably cheaper than the commercial kits have been described in the literature.< 5 The present prospective study evaluated the accuracy of one such preparation in a comparison with histologic analysis for the diagnosis of H. pylori infection. GASTROINTESTINAL ENDOSCOPY 503
K-M Chu, R Poon, H Tuen, et al.
Locally made rapid urease test and histology for diagnosis of H. pylori
Table 1. Indications for upper endoscopy in 2316 patients Indications
No. of patients (%)
Epigastric pain History of duodenal ulcer History of gastric ulcer History of gastritis History of gastrointestinal bleeding History of duodenitis History of perforated peptic ulcer History of pyloric stenosis Dysphagia History of stomal ulcer
1326 (57.3) 399 (17.2) 198 (8.5) 155 (6.7) 125 (5.4) 51 (2.2) 43 (1.9) 8 (0.3) 6 (0.3) 5 (0.2)
PATIENTS AND METHODS From February 1996 to November 1996, all patients undergoing elective upper endoscopy by members of the Division of Upper Gastrointestinal Surgery at our hospital were eligible for this study. Patients were excluded if they (1) were receiving a proton pump inhibitor or (2) within the past 6 weeks had received bismuth compounds, antibiotics, or eradication therapy for H. pylori. Patients who had received eradication therapy for H. pylori more than 6 weeks earlier were not excluded. Patients were consecutively enrolled and fasted for at least 8 hours before endoscopic examination. Endoscopic examination was performed under local pharyngeal anesthesia (Cetacaine spray; Cetylite Industries, Pennsauken, N.J.) with the patient lying in a left lateral position. Regardless of the endoscopic findings, three antral mucosal biopsy specimens were taken from within 3 cm of the pylorus and removed from the biopsy forceps (Olympus FB 25K; Olympus, Tokyo, Japan) with a needle. Two biopsy specimens were fixed with 10% formalin for histologic examination under hematoxylin and eosin stain with the result of the rapid urease test being unknown to the pathologist. Giemsa staining was done at the discretion of the pathologist. The presence ofH. pylori was established by its typical appearance on scanning along the mucosal surface and the individual gastric pits. A low density of/-/. pylori on histologic examination was defined as the identification of individual organisms, or small groups, covering less than one third of the gastric mucosal surface. 6 The remaining biopsy specimen was placed immediately, in the endoscopy unit, into a capped tube containing 1 ml of freshly prepared 5% (wt/vol) unbuffered urea in distilled water including two drops of 1% phenol red. The tube was placed in a rack at room temperature and was examined at 1 hour and 4 hours. The tube was labeled with the patient's name and identification number only. A single observer without knowledge of the patient's history and diagnosis read the test. A color change from yellow to pink in this "locally made rapid urease test" (LRUT) was recorded as a positive test. For the last 100 positive LRUTs, the time for color change was measured to the nearest minute. Continuous values were expressed as mean +_ standard error of the mean. Results of histologic examination were 504 GASTROINTESTINAL ENDOSCOPY
Table 2. Endoscopic findings in 2316 patients
Endoscopic findings
No. of patients with eradication therapy
Total No. of patients (%)
Normal Gastritis Duodenal ulcer Gastric ulcer Duodenitis Reflux esophagitis Carcinoma of stomach Stomal ulcer Gastric polyp
542 3 9 5 2 0 0 0 1
1238 (53.4) 337 (14,6) 310 (13.4) 212 (9.2) 135 (5.8) 30 (1.3) 28 (1.2) 16 (0.7) 10 (0.4)
Total
562 (24.3%)
2316 (100)
taken as the standard for comparison. The final result of the LRUT was judged at 4 hours. The sensitivity, specificity, and positive and negative predictive values of the LRUT were determined. The prevalence ofH. pylori infection in Hong Kong was previously reported to be about 55%. 7
RESULTS T h e r e w e r e 2316 p a t i e n t s w i t h a m e a n age of 56.7 _+ 0.4 y e a r s . T h e r e w a s a m a l e p r e p o n d e r a n c e ( m a l e / f e m a l e = 1.5:1). F i v e h u n d r e d sixty-two pat i e n t s (24.3%) h a d a h i s t o r y of e r a d i c a t i o n t h e r a p y for H. pylori. I n d i c a t i o n s for u p p e r e n d o s c o p y a r e s h o w n in T a b l e 1. T h e s e p a t i e n t s h a d u p p e r g a s t r o i n t e s t i n a l s y m p t o m s , k n o w n peptic u l c e r d i s e a s e s w i t h r e c u r r e n t s y m p t o m s or a f t e r t r e a t m e n t , or r e c e n t h i s t o r y of c o m p l i c a t e d peptic ulcer diseases. F i n d i n g s a t u p p e r e n d o s c o p y a r e s h o w n in T a b l e 2. N i n e h u n d r e d fifty-three p a t i e n t s (41.1%) w e r e f o u n d to h a v e b i o p s y s p e c i m e n s positive for H. pylori on histologic e x a m i n a t i o n . T h e d e n s i t y of H. pylori w a s c o n s i d e r e d to be low on histologic e v a l u a t i o n in 73 p a t i e n t s , s e v e n of w h o m h a d received e r a d i c a t i o n t h e r a p y for H. priori (p = N o t significant) (Table 3). T h e r e s u l t s of L R U T as c o m p a r e d w i t h histologic e v a l u a t i o n for H. pylori a r e d o c u m e n t e d in T a b l e 3. It is n o t e w o r t h y t h a t 63.8% (51 of 80) of falsen e g a t i v e t e s t s a t 4 h o u r s w e r e r e l a t e d to a low d e n s i t y of H. pylori. T h e sensitivity, specificity, a n d positive a n d n e g a t i v e p r e d i c t i v e v a l u e s of L R U T are s e e n in T a b l e 4. T h e s e n s i t i v i t y of t h e L R U T w a s l o w e r in p a t i e n t s w h o h a d r e c e i v e d e r a d i c a t i o n t h e r a p y for H. pylori. I n t h e l a s t 100 positive L R U T s , t h e m e d i a n t i m e for color c h a n g e w a s 8.0 m i n u t e s ( r a n g e 1 to 120 m i n u t e s ) . T w e n t y - t h r e e p e r c e n t of t e s t s w e r e positive w i t h i n 1 m i n u t e , w h e r e a s 90% of t e s t s w e r e positive b y 25 m i n u t e s .
VOLUME 46, NO. 6, 1997
Locally made rapid urease test and histology for diagnosis of H. pylori
Table 3. Results of locally made rapid urease testing at 4 hours in comparison with histologic examination Histology negative
Histology positive
Histology scanty positive
Total
Urease test negative Urease test positive
1340(493)
29 (9)
51 (7)
1420
23 (2)
851 (51)
22 (0)
896
Total
1363
880
73
K-M Chu, R Poon, H Tuen, et al.
Table 4. Sensitivity, specificity, and positive and negative predictive values of the locally made rapid urease test Sensitivity Specificity PPV NPV Overall Without previous eradication With eradication
(%)
(%)
(%) (%)
91.6 92.8 76.1
98.3 97.6 99.6
97.4 94.4 97.5 93.0 96.2 96.9
PPV, Positive predictive value; NPV, negative predictive value. 2316
Values in parentheses show history of eradication ofH. pylori.
DISCUSSION Although several noninvasive and invasive tests are available for the diagnosis ofH. pylori infection, histologic examination of biopsy specimens remains the gold standard. 2' s Histologic examination, however, is expensive and labor intensive, and the result is not usually available on the same day. It is highly desirable and cost effective for outpatients to have their result of H. pylori status during the same endoscopy visit so that they do not have to return again for the prescription of appropriate treatment. On the other hand, it is also desirable for inpatients, especially those with peptic ulcer hemorrhage, to have H. pylori status determined and appropriate t r e a t m e n t initiated as soon as possible. Rapid urease testing of gastric biopsy specimens is considered to be the initial test of choice in patients undergoing endoscopy because of its low cost, rapid availability of results, simplicity, and accuracy. 2, 3, 9 It was previously believed that urease was a normal component of gastric mucosal biochemistry. 1° After the first report by Langenberg et al. 11 of the production of urease by H. pylori, this property has formed the basis of several diagnostic tests for H. pylori, including urease testing of biopsy specimens and urea breath testing. The first urease test was described by McNulty and Wise in 198512 and used Christensen's 2% urea broth. Subsequently a number of modifications of this test have been reported. 4,5,13,14 The CLOtest (Delta West Ltd., Perth, Australia), which consists of an agar gel containing urea, phenol red, buffers, and a bacteriostatic agent in a sealed plastic slide, was the first urease test to become commercially available. To date, there are several commercial kits marketed for urease testing. 3 All commercial kits have shown good sensitivity (80% to 98%) and specificity (94% to 100%) for the diagnosis ofH. pylori infection. 3, s, 15 Commercial urease test kits cost about $4 to $7 per test. Although considered relatively low cost in comparison with histologic examination or culture of VOLUME 46, NO. 6, 1997
gastric biopsy specimens, 2, 3 cumulative costs will be substantial if numerous tests are performed. In these days of escalating health care costs, it would be prudent to adopt the use of a cheaper alternative if this can be shown to be accurate, and various locally produced rapid urease tests have been described. 4,5'z2-14 The LRUT described in the present study is similar to the one described by Arvind et al., 4 except for a lower concentration of urea in our preparation. The preparation of LRUT does not require special laboratory skills or equipment. It has to be prepared fresh each day, however, to avoid bacterial contamination with organisms such as Proteus or Pseudomonas which may produce a false-positive result with the production of low levels of urease over time. ~ It took nursing staff about 15 minutes daily to prepare the LRUT, and, in our setting, there was no need to pay additional costs for the labor involved. Excluding any labor for preparation, the LRUT costs about $0.01 per test. Assuming that a commercial kit costs $4 per test, in an endoscopy unit performing 5000 tests annually, for example, the estimated savings would be about $19,950 per year. Two biopsy specimens are adequate for an accurate diagnosis of H. pylori infection by histologic examination. 1~ The final result of the LRUT was read at 4 hours because it was considered to be the optimal time acceptable to an endoscopist seeking a same-day result. 3 Although incubation of the test material at 37 ° C shortens the time required for a positive urease test, 17 for simplicity it was not used in the present study; an incubator adds to the cost and complexity of the test. The LRUT was demonstrated to be highly accurate in the present study. In fact, its sensitivity, specificity, and positive and negative predictive values were comparable with those of commercial kits. 3 Although we have regarded the reading at 4 hours as the final result, 90% of tests were positive after 25 minutes. Consequently, the result could be conveyed to the patient during the same endoscopy visit. A correlation has been shown between the density of GASTROINTESTINAL ENDOSCOPY
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H. pylori in the biopsy specimens and the time for a positive urease test. 13 This may serve as an explanation for our findings that 63.8% of false-negative tests at 4 hours were related to low density of H. pylori. The false-negative rate may be reduced by monitoring the test for longer than 4 hours. In the present study, however, it would be impractical for our single observer to monitor the test for longer than 4 hours. In the study we included patients who had a history of eradication therapy for H. pylori. This accounted for the relatively high percentage of patients with normal endoscopic findings. The use of a urease test to confirm successful eradication of H. pylori after treatment is not recommended2 The present study showed a lower sensitivity for urease testing in patients with a history of eradication therapy. For patients undergoing repeat endoscopy after eradication treatment, an additional test such as histologic examination should, therefore, be performed to confirm or refute successful eradication of
H. pylori. The present study confirmed the value of the locally produced rapid urease test in clinical practice. Owing to its high accuracy, albeit with occasional false-negative results in patients with low density H. pylori, one can withhold processing of biopsy specimens taken for histologic examination until the result of the urease test becomes available. Such biopsy specimens could then be discarded if the urease test is positive. Alternatively, the biopsy specimens should be examined histologically if the urease test is negative; this is particularly relevant in patients with history of eradication treatment for
H. pylori. REFERENCES 1. NIH Consensus Development Pane] on Helicobacter pylori in peptic ulcer disease. Helicobacter pylori in peptic ulcer disease. JAMA 1994;272:65-9.
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Locally made rapid urease test and histology for diagnosis of H. pylori 2. Brown KE, Peura DA. Diagnosis ofHelicobacter pylori infection. Gastroenterol Clin North Am 1993;22:105-15. 3. Laine L, Lewin D, Naritoku W, Estrada R, Cohen H. Prospective comparison of commercially available rapid urease tests for the diagnosis of Helicobacter pylori. Gastrointest Endosc 1996;44:523-6. 4. Arvind AS, Cook RS, Tabaqchali S, Farthing MJG. Oneminute endoscopy room test for Campylobacter pylori. Lancet 1988;i:704. 5. Katelaris PH, Lowe DG, Norbu P, Farthing MJ. Field evaluation of a rapid, simple and inexpensive urease test for the detection of Helicobacter pylori. J Gastroenterol Hepatol 1992;7:569-71. 6. Price AB. The Sydney system: histological division. J Gastroenterol HepatoI 1991;6:209-22. 7. Ching CK. Yuen ST. Luk ISC. He J. Lain SK. The prevalence of Helicobacter pylori carrmr rates among the healthy blood donors in Hong Kong. J Hong Kong Med Assoc 1994;46:295-8. 8. Yousfi MM, E1-Zimaity HMT, Genta RM. Graham DY. Evaluation of a new reagent strip rapid urease test for detection of Helicobacter pylori infection. Gastrointest Endosc 1996;44: 519-22. 9. Cutler AF. Testing for Helicobacter pylori in clinical practice. Am J Med 1996:100:35S-41S. 10. Glick D. A histochemical study of urease in the human stomach with respect to acid secretion in ulcer and cancer. J Natl Cancer Inst 1949:10:321-30. 11. Langenberg ML, Tytgat GN, Schipper MEI, Rietra PJGM, Zanen HC. Campylobacter-like orgamsms in the stomach of patients and healthy individuals. Lancet 1984;i:1348. 12. McNulty CAM. Wise R. Rapid diagnosis of Campylobacterassociated gastritis. Lancet 1985;i:1443-4. 13. Hazell SL. Borody TJ, Gal A, Lee A. Campylobacterpyloridis gastritis. I. Detection of urease as a marker of bacterial colonization and gastritis. Am J Gastroenterol 1987;82:292-6. 14. Thillainayagam AV. Arvind AS. Cook RS. Harrison [G, Tabaqchali S. Farthing MJ. Diagnostic efficiency of an ultrarapid endoscopy room test for Helicobacter pylori. Gut 1991; 32:467-9. 15. Young EL, Sharma TK. Cutler AF. Prospective evaluation of a new urea-membrane test for the detection of Helicobacter pylori in gastric antral tissue. Gastrointest Endosc 1996:44: 527-31. 16. Thijs JC, van Zwet AA. Thijs WJ, Oey HB, Karrenbeld A~ Stellaard F, et al. Diagnostic tests for Helicobacter pylori: a prospective evaluation of their accuracy, without selecting a single test as the gold standard. Am J Gastroenterol 1996: 91:2125-9. 17. Laine L Estrada R. Lewin DN. Cohen H. The influence of warming of rapid urease test results: a prospective evaluation. Gastrointest Endosc 1996;44:429-32.
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