UREASE TEST: RATIONALE, PREPARATION, PROCEDURE - MEDICINE - 2025

The urease test or breath test is a specific test to indirectly detect the presence of Helicobacter pylori in the gastric mucosa. This microorganism is characterized by being a strong producer of urease, for this reason this test has a great sensitivity.

In addition, the test is considered to be highly specific because Helicobacter pylori is so far the only known bacterium that can lodge, survive and cause pathology in the gastric mucosa.

Graphic representation of the microorganism Helicobacter pylori and breath test or urease test. Source: Pixabay.com

On the other hand, urease is not an enzyme that can be found in the stomach physiologically or for different causes. So if the breath or urease test is positive there is no question that H. pylori is present.

Taking into account that Helicobacter pylori has a high prevalence in the world population and that it represents a risk factor in suffering from gastric cancer, it is important that an early diagnosis be made.

For this, there are various diagnostic methods that detect the presence of Helicobacter pylori, some are invasive and others are non-invasive.

There is no doubt that gastric mucosa biopsy is one of the most reliable techniques, but its disadvantage is that it is an invasive technique, making it difficult to perform. Also, it only tests a small portion of the total stomach.

On the other hand, it must be considered that this infection usually begins in childhood and therefore it is necessary that there are non-invasive diagnostic techniques. Non-invasive techniques with great specificity and sensitivity include the urease test or the breath test.

Basis

This technique is an indirect method to diagnose the presence of Helicobacter pylori. This is based on the detection of urease production by the microorganism. To do this, the patient is given a dose of 14-C-labeled urea.

If the microorganism is present it will rapidly break down urea into ammonia and CO ₂. The CO ₂ generated passes into the blood and from there to the lungs, being eliminated by breathing (exhaled air). The breath test is based on collecting that exhaled air and detecting or measuring radioactivity.

If radioactivity is detected, the urease test for Helicobacter pylori is positive. This technique has 97-100% sensitivity and specificity.

Preparing the patient to perform the breath test or urease test

To perform this test, the patient must prepare 2 weeks to 4 weeks in advance and must meet certain requirements:

-The patient must not have been on antibiotic treatment for at least 1 month prior to the study.

-On the other hand, the patient may not have been or be under treatment with certain medications, such as: proton pump inhibitors (gastric protectors), medications that contain bismuth or sucralfate. The presence of these drugs provides false negatives.

-The day of the test you must go completely fasting.

Urease test procedure

Test with C14

The patient is given a 1 mg 14 C-urea capsule with 20 ml of water. It can also be done with C13-labeled urea but the procedure is more complicated and expensive. For this reason the most widely used is the C14 isotope.

When ingesting the capsule the patient should avoid touching the lips or cheeks. After 3 minutes the patient should drink 20 ml more of water.

From this moment they wait 7 minutes. Once the time has elapsed, the patient is asked to exhale air through the mouth through a hollow cannula, the opposite end of which will be immersed in 2.5 ml of breath container liquid.

This liquid is blue in color and is designed to become crystalline when it receives 2 mmol of carbon dioxide. The next step consists of adding 10 ml of the scintillation liquid, mixing it and leaving it to rest for 1 hour.

It is then taken to specialized equipment called a beta scintillation counter. Finally, to calculate the disintegration per minute, the following formula is used:

Source: 2. Aguilar C, Saavedra P, Mendoza G, Bussalleu A, Cok J, Martínez F and et al. Study of the urease test or breath test (TA) and correlation with gastric biopsy for the detection of Helicobacter pylori (Hp) in dyspeptic patients of the Hospital Nacional Cayetano Heredia - Lima. Rev. gastroenterol. Peru, 2007; 27 (2): 172-176. Available at: http: //www.scielo

Test with C13

The procedure is similar but has some changes. In this case, two breath samples should be taken, one at the beginning and one after 20 minutes of consuming the 13-C-labeled urea.

The samples are passed through an apparatus that detects the C13 concentration by colorimetry. The measuring instrument is called a spectrophotometer.

A low baseline C13 value with a significant increase in C13 in the second sample demonstrates a positive result.

Utility

Gastric infection by Helicobacter pylori reaches alarming figures worldwide; statistics express that almost 50% of the population may be infected by this bacterium.

Helicobacter pylori causes chronic gastritis and peptic ulcers. In addition, there are studies that show that this bacterium is a risk factor for later suffering from gastric cancer in a proportion of 2-6%. These figures are important, since it is known that this neoplasm is the second oncological pathology that causes more deaths worldwide.

It should be noted that people are susceptible to being infected with this bacteria from an early age. Due to all this, it is important to have diagnostic methods that are easy to use, accessible and at the same time highly sensitive and specific.

Gastric mucosa biopsy along with rapid urease testing has long been considered the “Gold Standard” tests for the detection of Helicobacter pylori, but they have the disadvantage that they are both invasive tests.

In this sense, Aguilar et al. Demonstrated that the urease test or breath test offers results comparable to those obtained with the gastric biopsy and the rapid urease test. In addition, it also serves to evaluate the follow-up of treatment.

That is why some countries use the breath test as a routine test for the diagnosis of this bacterium. Although it should be noted that the breath test is not the only option, there are other non-invasive, inexpensive and reliable methods that are also useful, such as the detection of H. pylori antigen in stool.

Serology, on the other hand, despite being useful, is not good for monitoring.

Advantage

-Method with high sensitivity and specificity

-Non-invasive

-Easy to perform in the case of using C14 isotope

-Economic if done with C14 isotope.

-The C13 isotope is not radioactive and is suitable for children and pregnant women.

-Evaluate the entire stomach.

Disadvantages

-The method that uses the C14 isotope cannot be used in pregnant women and children because it is radioactive. In these cases it is preferable to use the C13 isotope, however the latter has the drawback that the technique is more laborious and expensive.

References

1. Silva R, Casanova G, Albarracín Z, García M, Torres R. Breath test and histopathological findings associated with Helicobacter pylori infection. Gen 2012; 66 (2): 93-99. Available at: scielo.org
2. León-Barúa R. Meaning of the positive serology test for the detection of Helicobacter pylori. Rev Med Hered, 2004; 15 (3): 123-124
3. Nguyen Thi H, Falcón Márquez R, Vázquez Ramudo S, Almaguer Rodríguez T, Tamayo Brito C, Corrales Sánchez R and et al. Evaluation of the performance of two tests for the detection of Helicobacter pylori antigen in feces. Rev Cubana Med Trop; 2017; 69 (1): 1-7. Available at: scielo.sld.
4. Rodríguez A, Alvarado J, Sandler R, Hani A, Sanmiguel C, Gómez G. Association between Helicobacter pylori infection and gastric cancer in Colombia. Acta Med Colomb 2000; 25 (3): 112-116). Available at: actamedicacolombiana.com
5. Espinoza V, Tabori H, Meza C, Bussalleu A, Vásquez L, Aguilar V, et al. Validation of the rapid urease test for the detection of Helicobacter pylori at the Cayetano Heredia National Hospital, Lima, Peru. Rev. gastroenterol. Peru 2017; 37 (1): 53-57. Available at: scielo.org.