interference with the [14C]carbon urea breath test for the
detection of Helicobacter pylori infection
received March 21st, 2000, Revised May 3rd, 2000; Accepted June 26th,
Department of Radiology, Health Sciences Centre, Winnipeg, Manitoba, Canada
Medicine, Diagnostic Imaging, Foothills
Medical Centre, Calgary, Alberta, Canada
Medicine, Dept. of Diagnostic Radiology, Queen Elizabeth
II Health Sciences
Centre, Victoria General Site, Halifax, Nova Scotia, Canada
Helicobacter pylori bacteria reside in the mucosal
lining of the stomach where, due to a variety of factors, the infection
predisposes patients to peptic ulcer disease. Detection of H. pylori
is important in the treatment and follow-up of patients with peptic ulcer
disease and the urea breath test is the method of choice. This article
will briefly review the methods for diagnosing H. pylori,
emphasizing the [14C]urea breath test. The agents which can
interfere with the results of the breath test will be reviewed and the
role of the consulting pharmacist will be discussed.
The diagnosis and treatment of
ulcers has changed considerably during the last two decades since Warren
and Marshall implicated Helicobacter pylori in the genesis of
peptic ulcer disease (1). Subsequently, there has been
general agreement in the medical community that bacterial infection with
H. pylori is causally related to cases of duodenal and gastric
ulceration and to chronic gastritis (2-4). While approximately 30 to 50
% of asymptomatic controls culture positive for H. pylori, more
than 90 % of patients presenting with duodenal or gastric ulcer are
positive (5). Infected adults are at a 3.2 to 5.5 fold increased risk of
developing peptic ulcer disease compared to the uninfected population,
but the development of clinically significant sequelae seems to depend
on the pathogenicity of the H pylori strain (5, 6). Eradicating
H. pylori heals ulcers independent of other therapy and the addition
of antibiotics to the therapeutic regimen has been shown to dramatically
reduce the rate of ulcer recurrence. The Consensus Development Panel of
the National Institutes of Health now recommends that all patients
diagnosed with peptic or duodenal ulcers that are infected with H.
pylori receive antimicrobial therapy (7).
Although most ulcer therapy
provides excellent initial healing, the relapse rate between various
regimens can differ significantly. The most effective therapy of H.
pylori requires multiple drug treatment involving various
combinations of antibiotics, histamine blockers, proton pump inhibitors
and bismuth salt preparations (8, 9). In addition to potential classical
drug interactions, the diagnostic tests used to confirm eradication are
also subject to interference from many drugs. Therefore, the pharmacist
has an important role in both the treatment and diagnosis of peptic
colonize the gastric epithelium in the stomach, causing acute
inflammation progressing to superficial gastritis then to chronic
atrophic gastritis. Acute infection leads to parietal cell dysfunction
and acute hypochlorhydria, which increases gastrin and acid secretion.
However the gastric pH soon returns to normal due to the release of
bacterial urease which neutralizes the increased acid. This urease,
which shows little difference between bacterial strains, is important in
establishing chronic infection. The bacteria also induce a local
inflammatory response attracting neutrophils, T cells, plasma cells and
macrophages, but the bacteria, in their niche in the gastric mucosa, are
not readily accessible to the antibodies produced. The H. pylori strains
most involved in peptic ulcer also produce cytotoxins which promote the
inflammatory response and reduce duodenal bicarbonate secretion (5).
The presence of H. pylori
can be diagnosed by different modalities which exploit various
properties of the bacteria. These include endoscopy followed by
histologic analysis, bacterial culture or urease testing of the biopsied
sample, serologic detection of the antibody response, or detection of
urease production by the carbon urea breath test (10).
Endoscopy with biopsy is the gold
standard for detection of H. pylori, however, it is a relatively
expensive and invasive procedure that is dependent on an experienced
observer (10). Detection of the bacteria in a culture of the biopsy
material is comparable to the precision of histologic examination of the
specimen (specificity is 100 % for both procedures), but is more
difficult to perform. The sensitivity (80 to 95 %) of histology is
somewhat higher than tissue culture (sensitivity 60 to 90 %) but the
need for multiple specimens to be examined by an experienced pathologist
adds to the cost of endoscopy. Testing the biopsy sample for the
presence of urease is a much simpler, quicker and less expensive test
than either culture or histology and has high sensitivity (90 to 95 %)
and specificity (98 to 100%). However, a biopsy sample is still
Serology tests detect the
antibodies (determined by using radioimmunoassay techniques) produced in
response to the infection and are useful to determine whether the
patient has been exposed to H. pylori. The test has good
specificity (98 to 100 %) and is the only procedure which is not
influenced by prior antibiotic, bismuth compound, or omeprazole therapy.
Unfortunately, a positive serology test can only presume current
infection since the serum antibody titres to the bacteria decline slowly
after eradication therapy (11). Therefore, long term follow up is
required to ascertain the magnitude of this reduction limiting the use
of serology in patient follow up post antibiotic treatment.
The [14C]carbon urea
breath test is a sensitive, non-invasive test which can be used to
determine the presence of H. pylori prior to initial treatment
and for follow up after antibiotic therapy (12-15). The test is based on
the detection of the enzyme urease, which is secreted by the bacteria
to convert urea to ammonia. This produces an alkaline environment
which facilitates their survival in the mucosal layer of the stomach. In
the presence of urease, the [14C]urea
is converted into [14C]bicarbonate and ammonium ions. The [14C]bicarbonate
anion is absorbed into the blood stream, transported to the lungs, and
subsequently exhaled as [14C]CO2.
Detection of radioactive [14C]CO2
in the breath samples indicates an H. pylori infection, as
other urease producing bacteria do not colonize the stomach (16).
The urea breath test can also be
performed using non-radioactive 13C enriched urea (17). The
disadvantage of using the 13C
isotope is that a mass spectrometer is required for its detection. As
this equipment is expensive and not readily available in most centres, 13C
breath samples must typically be transported to another facility for
analysis. Recent advances in laser (18) and infrared (19) spectroscopy
show promise as lower cost replacements for mass spectroscopy.
In contrast, 14C
can be readily detected using a liquid scintillation counter which is
relatively inexpensive and not uncommon in hospital centres. In
addition, the results can be available on the same day that the test is
The urea breath test is a
sensitive, specific, noninvasive and more cost effective test than
endoscopy, and is the preferred method to check for eradication after
Patients should not be evaluated
too soon following anti-ulcer therapy to avoid false negative test
results. The bacterial load can be greatly reduced immediately following
treatment with antibiotics, cytoprotectives and proton pump inhibitors
(PPI’s). If the test for eradication is performed too soon,
surviving bacteria that could re-colonize the stomach may not be
Patients must fast for 4 to 6
hours prior to ingestion of the [14C]urea
capsule or liquid. Any food in the stomach will dilute the product and
delay excretion of the [14C]carbon
dioxide. If the [14C]urea
is administered as a liquid, the patients must rinse their mouths prior
to ingestion to remove any urease producing commensal flora that may be
present. Dentures should also be removed to avoid trapping of the fluid
between the gums and dentures, which could result in a false positive
Prior to ingestion of [14C]urea,
the patients provide a 'baseline' sample by blowing into a
precisely titrated basic solution of benzethonium hydroxide
(Hyamine hydroxide in methanol) containing an acid/base indicator such
as phenolphthalein, bromothymol or thymolphthalein blue (Figure
solution 'traps' the exhaled carbon dioxide by the formation of a
carbamate and the liberation of hydrogen ions into the basic solution.
When sufficient CO2 has been exhaled to convert all the
benzethonium hydroxide to the carbamate, the solution becomes acidic and
the indicator changes color. A capsule or liquid containing the [14C]urea
is then swallowed and a series of breath samples are obtained at
intervals up to 30 minutes after ingestion. The amount of radioactivity
present in each sample represents the amount of [14C]CO2 exhaled which is
proportional to the amount of [14C]urea metabolized by the bacteria. An
alternative protocol can be performed by having the patient blow into a
mylar balloon 10 minutes after swallowing a capsule containing the [14C]urea.
The contents of the balloon are transferred via a pump into the trapping
solution which is then processed as explained above (21).
Many protocols require multiple
sampling to calculate the total amount of [14C]CO2 produced as described
by Henze et al (13) who preferred the multiple sampling technique
to generate a curve describing the fraction of the dose excreted as a
function of time.(21).
1: Schematic representation of the detection of H. pylori
infection using the [14C] Urea Breath Test.
The area under the curve was
evaluated to calculate the total amount of [14C]CO2 excreted. The accuracy
of a single sample taken at 10 or 20 minutes after ingestion of the
radiolabelled urea (14,15) has recently been validated. Desroches et
al (15) suggested using a 2 mmol solution of benzethonium hydroxide
and a single breath sample obtained 20 minutes after ingestion of 5 mCi
Excretion of more than 0.33 % of the
ingested dose was considered positive for the presence of H.
pylori. The sensitivity and specificity of the single breath
protocol was 98 % and 100 % respectively.
The ingested [14C]urea
is rapidly excreted from the body as either [14C]CO2
in the breath or as intact [14C]urea
in the urine (12). In uninfected individuals, it is estimated that up to
30 % of the radioactivity is excreted in the breath as
with the remaining 70 % excreted by the kidneys unchanged.
Respiratory excretion of [14C]CO2
is increased to 60 % in patients infected with H. pylori, with
the remainder excreted in the urine as [14C]urea
(12). The radiation exposure from a 1 mCi
dose of 14C is estimated to be equivalent to the amount of
radiation received by the patient from the natural environment over a
period of 11 hours (22).
Interference with the Urea Breath Test
breath test is dependent on the concentration of H. pylori
present in the gut. Therefore any drug which suppresses the growth of
bacteria can theoretically affect the results of the urea breath test.
As well, other drugs
commonly used in the treatment of ulcers can potentially interact with
the test. Some of these drug-test interactions are well documented while
others remain speculative. A summary of these interactions is provided
in Table 1.
1. Pharmaceuticals Interfering with the 14C Urea Breath
classes except: Vancomycin, Nalidixic
Acid, Trimethoprim, Amphotericin
or bactericidal activity
medication 30 days prior to test
medication 30 days prior to test
or bacteriostatic activity.
medication 7-14 days prior to test
Famotidine, Nizatidine, Ranitidine
promote urease producing oral flora. May promote H. pylori
medication 12-24 hours prior to test
in urease activity. May erroneously decrease result values.
contraindicated but should be reduced if possible
studies have shown that a wide range of antibiotics possess varying
inhibitory or bactericidal activity against H. pylori including
beta-lactams, macrolides, nitrofurans, and quinolines, with the exception
of vancomycin, nalidixic acid, trimethoprim, and amphotericin B (23, 24). In order to ensure that complete eradication of H.
pylori has occurred, it is essential that antibiotic treatment for any
disorder has been completed at least 30 days prior to testing for H.
Bismuth salts must also be
discontinued for 30 days prior to the urea breath test. Bismuth has also
been shown to inhibit H. pylori activity due to both its
bactericidal activity and its cytoprotective effect (24-26). Electron
microscopy of gastric biopsy specimens following treatment with bismuth
demonstrated coating of the
bacteria with the bismuth compound followed by swelling and lysis of the
organism. It is also possible that bismuth inhibits bacterial enzymes
which could disrupt cell metabolism, rendering the bacteria susceptible to
the body's normal defenses (26).
Proton pump inhibitors such as
omeprazole, lansoprazole, or pantoprazole have bactericidal activity
against H. pylori in the early stages of infection, when the number
of bacteria colonizing the gut is low. A bacteriostatic effect has been
observed when bacterial densities are very large (27). Procedure
guidelines for the urea breath test typically suggest discontinuing PPIs
two weeks prior to testing (28). A one week hiatus from the drug may be
appropriate considering that many patients rely on the use of PPIs to
relieve the symptoms of gastritis or ulcer.
H2 receptor antagonists and
sucralfate were found ineffective in the suppression of H. pylori (2,24).
H2 receptor antagonists were found to heal the gastric wall, but left the
bacteria adhering closely to the gastric mucosa. They are used sometimes
to reduce the painful gastric symptoms experienced by
patients who must stop PPIs prior to the urea breath test. However,
H2 receptor antagonists have been implicated in the proliferation of H.
pylori (23) and in the growth of urease producing commensal oral flora
due to an increase in gastric pH (12). For these reasons, patients are
often requested to stop taking H2 receptor antagonists for 12 to 24 hours
prior to the urea breath test.
Antacids have also been shown to
suppress bacterial growth for a short period of time after administration.
Berstad et al reported a 30% decrease in urease activity
immediately following treatment with antacids (29) but the urease activity
rebounded to pretreatment levels within 2 weeks. Despite the reduction,
the urease activity immediately
post antacid treatment was still significantly higher than in those
individuals with no evidence of H. pylori infection. Consequently,
antacids are not typically contraindicated prior to performing the [14C]carbon
urea breath test.
Treatment to eradicate H. pylori
has dramatically changed the natural history of peptic ulcer disease from
a chronic, relapsing disorder to a simple, one treatment cure. The [14C]carbon
urea breath test is a easy, non-invasive test that accurately predicts the
presence of H. pylori in
affected patients. In addition to counselling for standard potential
adverse medication effects and interactions, physicians, pharmacists, and
patients should also be aware that any medication that temporarily
suppresses these bacteria should be discontinued prior to performing the
urea breath test in order to increase the reliability of the results.
The authors would like to thank Ms.
Rosina Kanerva, Foothills Medical Centre for illustrating Figure
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Copyright © 1998 by the Canadian Society for Pharmaceutical Sciences.