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Urea C 14 (Systemic)

Primary: DX202

Commonly used brand name(s): PYtest.

Note: For a listing of dosage forms and brand names by country availability, see Dosage Forms section(s).

Not commercially available in Canada.


Diagnostic aid (Helicobacter pylori infection)—



Ulcer, gastric, Helicobacter pylori –associated (diagnosis)—Urea C 14 is indicated for use in the detection of gastric urease as an aid in the diagnosis of Helicobacter pylori (H. pylori ) infection in the stomach, by using a scintillation counter to measure 14CO 2 in breath samples {01}.

Note: The oral capsules are meant to be used when analysis is planned at the site where the sample is taken {01}.
The test has been evaluated in outpatients attending for elective endoscopy {01}.
The test has not been evaluated for monitoring the efficacy of antimicrobial therapies for H. pylori infection {01}.

Physical Properties

Radionuclide (half-life)  Mode of decay  Principal photon emissions (keV) 
C 14 (5730 years)  Beta emission  Beta (mean): 49 keV 
Beta (max): 156 keV 


Mechanism of action/Effect:

Urease is present in mammalian cells only when bacteria are present. Presence of urease is not a specific indicator for presence of H. pylori bacteria, but other bacteria are not usually found in the stomach. If gastric urease is present, the ingested urea is split to form CO 2 and NH 3 at the interface between the gastric epithelium and lumen; CO 2 is absorbed into the blood and exhaled in the breath. Therefore, urea C 14 split by urease will be exhaled as 14C-labeled CO 2, which can be measured with a liquid scintillation counter. {01}


Gastric, by hydrolysis, by urease associated with the presence of bacteria {01}.



For 14CO 2: For portion of urea C 14 hydrolyzed by H. pylori urease—15 minutes {01}.

For urea C 14: Portion not hydrolyzed by H. pylori urease—12 hours {01}. About 10% of the C 14 remains in the body at 72 hours and is gradually eliminated with a biological half-life of 40 days {01}.

Time to peak concentration:

14CO 2 in breath—10 to 15 minutes {01}.

    Respiratory— 14CO 2 produced by hydrolysis of urea by H. pylori urease {01}.
    Renal—Portion of urea C 14 not hydrolyzed by H. pylori urease (unchanged) {01}.

Note: Maximum excretion of urea (in case of overdose) occurs at a urine output of ³ 2 mL per minute {01}.

Precautions to Consider


Studies have not been done {01}.


Studies have not been done {01}.

Studies have not been done {01}.

Studies have not been done in humans or animals {01}.

It is recommended that risk-benefit be considered before use of urea C 14 in pregnant women {01}.

FDA Pregnancy Category C {01}.


It is not known whether urea C 14 is distributed into human breast milk {01}. Caution is recommended in using urea C 14 in women who are breast-feeding {01}.


Appropriate studies on the relationship of age to the effects of urea C 14 have not been performed in the pediatric population {01}. However, pediatrics-specific problems that would limit the usefulness of this agent in children are not expected {01}. No dosage adjustment is necessary {01}. The child must be able to swallow the intact capsule and to blow into a straw {01}.

Drug interactions and/or related problems
See Diagnostic interference.

Diagnostic interference
The following have been selected on the basis of their potential clinical significance (possible effect in parentheses where appropriate)—not necessarily inclusive (» = major clinical significance):

With results of this test

Due to other medications:
» Antibiotics and
» Bismuth-containing preparations    (ingestion within 4 weeks prior to performing the test may lead to false negative results {01})

» Proton pump inhibitors (e.g., omeprazole) and
» Sucralfate    (ingestion within 2 weeks prior to performing the test may lead to false negative results {01})

Due to medical problems or conditions:
» Achlorhydria (e.g., after resective gastric surgery)    (false positive results may occur due to bacterial overgrowth {01})

Bezoar or
Food in the stomach or
Gastroparesis    (may prevent contact of the isotope with the gastric mucosa; in addition patient may be achlorhydric and/or have bacterial overgrowth [non–H. pylori urease]; effect on test results unknown {01})

Infection with Helicobacter other than H. pylori (e.g., H. heilmanni )    (false positive results may occur; very rare {01})

Resective gastric surgery    (rapid emptying of the isotope from the stomach may lead to false negative results {01})

Medical considerations/Contraindications
The medical considerations/contraindications included have been selected on the basis of their potential clinical significance (reasons given in parentheses where appropriate)— not necessarily inclusive (» = major clinical significance).

See also Diagnostic interference.

Risk-benefit should be considered when the following medical problem exists
Sensitivity to urea C 14

Side/Adverse Effects

Note: No side/adverse effects were reported in clinical trials with this agent {01}.
The estimated radiation dose equivalent from administration of a single 1-microcurie capsule of urea C 14 is about 0.3 mrem (milli-roentgen-equivalent-man). According to the Nuclear Regulatory Commission, any dose below 5 to 10 mrem is below regulatory concern. {01}

For more information on the management of overdose or unintentional ingestion, contact a Poison Control Center (see Poison Control Center Listing ).

Clinical effects of overdose
Risk from radiation is negligible even with ingestion of 1000 capsules (0.3 rem [roentgen-equivalent-man]) {01}.

Treatment of overdose
To enhance elimination—The patient should drink one glass of water (150 mL) every hour to speed elimination of the isotope {01}. (Maximum elimination of urea occurs at a urine output of ³ 2 mL per minute {01}.)

Patient Consultation
As an aid to patient consultation, refer to Advice for the Patient, Urea C 14 (Diagnostic) .

In providing consultation, consider emphasizing the following selected information (» = major clinical significance):

Description of use
Action in the body: Amount of enzyme associated with bacteria in the stomach is determined by measurement of radioactivity in the breath

Small amounts used in diagnosis; radiation exposure is low

Before having this test
»   Conditions affecting use, especially:
Sensitivity to urea C 14
Other medications, especially antibiotics, bismuth-containing preparations, proton pump inhibitors, and sucralfate

Other medical problems, especially achlorhydria due to resective gastric surgery

Preparation for this test
» Not eating or drinking for 6 hours before the test

» Not handling the capsule directly, which could interfere with test results; tipping the capsule directly into the mouth from a cup

» Swallowing the capsule whole, without chewing (to avoid contamination by bacteria in the mouth)

General Dosing Information
It is recommended that test results be evaluated in conjunction with clinical signs and patient history when diagnosing H. pylori infection. An indeterminate or negative test result does not completely rule out the possibility of H. pylori infection; repetition of the test or use of an alternative diagnostic method is recommended if clinical signs and patient history suggest H. pylori infection. {01}

See the manufacturer's package insert for list of materials needed but not provided in the test kit {01}.

The manufacturer's package insert should be consulted for specific test procedure {01}.

It is necessary for the patient to fast for six hours prior to the test {01}.

The patient should be seated at rest while the test is conducted {01}. The capsule is swallowed whole with 20 mL of lukewarm water; this is followed by another 20 mL of lukewarm water (to ensure that the capsule has not lodged in the esophagus and has reached the gastric mucosa) {01}.

An accurate test result depends on production of a minimum of 1 millimole (mmol) of CO 2. While the amount of breath required to provide 1 mmol of CO 2 varies depending on the amount of CO 2 a patient is producing, and because a full balloon typically contains at least 1 mmol of CO 2, it is recommended that the balloon be completely filled. {01}

The recommended method of breath sample collection is to breathe into a balloon and not into a vial, since with the latter method patients may come into direct contact with the hyamine reagent. (Although hyamine will not cause serious poisoning, it can cause local irritation to the skin or mucous membranes.) If the vial collection method is used and some collection fluid splashes onto the skin or eyes, those areas should be washed immediately with water. If the collection fluid is accidentally ingested, it is recommended that the mouth be washed with water and that the patient drink 250 mL of water immediately. A poison information center may be consulted for additional facts on hyamine. {01}

Scintillation fluid comes in many formulations, usually consisting of a mixture of toluene and various cyclic hydrocarbons, and is flammable. Biodegradable formulations do not exist. {01}

Oral Dosage Forms


Usual adult and adolescent administered activity
Diagnosis of Helicobacter pylori –associated gastric ulcer
Oral, 0.037 megabecquerel (1 microcurie), followed by collection of breath sample after 10 minutes {01}.

Note: The sample is read repeatedly until values 10 minutes apart are similar. Results are interpreted according to the following criteria {01}:    • < 50 disintegrations per minute (DPM)—Negative for H. pylori .
   • 50 to 199 DPM—Indeterminate for H. pylori .
   • ³ 200 DPM—Positive for H. pylori .

Usual pediatric administered activity
See Usual adult and adolescent administered activity {01}.

Strength(s) usually available

0.037 megabecquerel (1 microcurie) (Rx) [PYtest (urea is adsorbed on sugar spheres and colored yellow with fluorescein)]

Packaging and storage:
Store between 15 and 30 °C (59 and 86 °F), in a tight container, in an area designated by each individual institution's regulations {01}.

Auxiliary labeling:
   • Swallow capsule whole.

Note: Caution—Radioactive material.

Developed: 09/30/1998

  1. PYtest package insert (Tri-Med Specialties—U.S.), Rev 8/11/97.