Uses For Pytest
Urea C 14 is a radiopharmaceutical. It is used to diagnose stomach ulcers caused by a certain kind of bacteria known as Helicobacter pylori or H. pylori.
This agent is taken by mouth. If any H. pylori bacteria are present in the stomach, they will cause the urea C 14 to be broken down into radioactive carbon dioxide gas. When you breathe out by the mouth, the amount of radioactive carbon dioxide can be measured to see whether the bacteria are in your stomach.
This agent is a radioactive agent. However, with the small amounts in the capsule that is used for the test, the radiation your body receives is very low and is considered safe.
This agent is to be given only by or under the direct supervision of a doctor with specialized training in nuclear medicine.
Pytest Side Effects
Along with its needed effects, a medicine may cause some unwanted effects. This agent does not usually cause any side effects. However, if you notice any unusual effects, check with your doctor.
The urease enzyme is not present in mammalian cells, so the presence of urease in the stomach is evidence that bacteria are present. The presence of urease is not specific for H.pylori, but other bacteria are not usually found in the stomach. The principle of the breath test is shown in Figure 1.
Figure 1: Principle of Breath Test
To detect H.pylori, urea labeled with 14C is swallowed by the patient. If gastric urease from H.pylori is present, urea is split to form CO2 and NH3 at the interface between the gastric epithelium and lumen and 14CO2 is absorbed into the blood and exhaled in the breath.
Following ingestion of the capsule by a patient with H.pylori, 14CO2 excretion in the breath peaks between 10 and 15 minutes and declines thereafter with a biological half-life of about 15 minutes. 14C-urea that is not hydrolyzed by H.pylori is excreted in the urine with a half-life of approximately 12 hours. About 10% of the 14C remains in the body at 72 hours and is gradually excreted with a biological half-life of 40 days.
Indications and Usage
PYtest1 (14C-Urea Breath Test) is indicated for use in the detection of gastric urease as an aid in the diagnosis of H.pylori infection in the human stomach. The test utilizes a liquid scintillation counter for the measurement of 14CO2 in breath samples.
Dosage and Administration
As shown in Figure 2, the PYtest1 Kit contains:
- PYtest1 capsule
- Two 30 mL disposable cups
- One drinking straw
- One mylar collection balloon
- One report form
- One mailing box with labels2
Figure 2: PYtest1 Kit2 The kit includes analysis by Kimberly-Clark of one balloon from one patient at one time point.
Materials Needed but not Provided
- Stopwatch/Timer capable of timing an interval up to 10 minutes.
- Water (40mL)
One PYtest1 capsule.
- Inform the patient to fast for 6 hours prior to the test.
- The patient should be off antibiotics and bismuth for 1 month, and proton pump inhibitors and sucralfate for 2 weeks prior to the test.
- Have patient sitting at rest while doing the test.
- The capsule should not be handled directly as this may interfere with the test result.
- To avoid contamination by bacteria in the mouth, the capsule should be swallowed intact. Do not chew capsule.
Step by Step Procedure for Balloon
|Before the test|| |
|Minus 1|| |
|0 minute|| |
|3 minutes||Ask the patient to drink another 20 mL of lukewarm water (in case the capsule may have lodged in the esophagus and not yet reached the gastric mucosa).|
|10 minutes|| |
|After the test||Place the filled balloon and breath test report in the box and forward to Kimberly-Clark for analysis.|
A minimum of 1 mM of CO2 is required to perform analysis of a breath sample. The amount of breath required to provide 1 mM of CO2 varies depending on the amount of CO2 the patient is producing. Since a full balloon typically contains at least 1 mM of CO2, the balloon should be completely filled.
|Interpretation of results (10 minute sample)|
|<50 DPM||Negative for H.pylori|
|50-199 DPM||Indeterminate for H.pylori|
|≥200 DPM||Positive for H.pylori|
The indeterminate result should be evaluated by repeating the PYtest1 or using an alternative diagnostic method. If repeat breath testing is undertaken, careful history to exclude confounding factors should be obtained. If confounding factors are present, wait an appropriate time (refer to Table 4) before repeating the PYtest1.
The cutoff point of 50 DPM was determined to be the mean + 3SD of results obtained in patients who did not have H.pylori.
DPM = Disintegrations per minute
|Recent antibiotic or bismuth (Pepto-Bismol, etc.)||false neg.||Relapse of partially treated Hp may take 1-4 weeks.|
|Omeprazole (or other proton pump inhibitors)||false neg.||These agents suppress Hp in 40% of patients. Discontinue for at least 2 weeks before performing the PYtest1.|
|Resective gastric surgery||false neg.||Isotope may empty rapidly from the stomach.|
|Resective gastric surgery||false pos.||Patient may be achlorhydric and have bacterial overgrowth (non-Hp urease).|
|Food in stomach (also bezoar, gastroparesis)||unknown||Isotope may not come into contact with gastric mucosa. Patient may be achlorhydric and/or have bacterial overgrowth (non-Hp urease).|
As shown in Figure 3 approximately 30% of patients tested will be positive for H.pylori.
Figure 3: Histogram showing DPM distribution for the PYtest1.
Note: DPM groupings were calculated on a logarithmic scale. Empty DPM groupings were not included. Chart includes all patients from Studies 1 and 2.
Frequency of DPM group includes samples with DPM < Group Name.
DPM = Disintegrations per minute
Gold Standard = Agreement between histology and CLOtest1
If the capsule is damaged or appears abnormal in any way, it may give inaccurate results.
PYtest1 Kit (14C-Urea Breath Test) is supplied as a kit containing a PYtest1 Capsule, a clear gelatin capsule containing 1µCi of 14C-urea and breath collection equipment.
PYtest1 Capsules are also supplied separately in unit dose packages of 1,10 and 100.
The PYtest1 Capsule has a shelf life of two years. The expiration date is printed on the capsule label.
PYtest1 Capsules and Kit should be stored at 15°-30°C (59°-86°F) in an area designated by each individual institution's regulations.
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