Biochemistry/ Immunology

Hello to all of you. For this week, I shall talk about a very special test called the Urea Breath Test (UBT). Firstly, we have to know that this is not a commonly requested test. It is unique in the sense that detection of an illness can be done using the patient's breath sample instead of common samples like blood or urine.



Purpose of UBT

To identify infections by Helicobacter pylori, a spiral bacterium implicated in gastritis, gastric ulcer, and peptic ulcer disease.


Helicobacter pylori is a helical shaped, gram-negative bacterium. It infects various area of stomach and duodenum. Its helical shape is thought to have evolved to penetrate and favour its motility in the mucus gel layer.

Helicobacter pylori

Principle of UBT

Patient will swallow urea labelled with an uncommon isotope, either radioactive carbon-14 or non-radioactive carbon-13. For the two different forms of urea, different instrumentation is required; carbon-14 is normally measured by scintillation, whereas carbon-13 by isotope ratio mass spectrometry (IRMS). For carbon-13, a baseline sample is taken before taking the urea tablet and used to compare with the post urea sample. In this case, my lab uses the carbon-13 method and so 2 samples are collected from each patient.

UBIT-IR300 is an infrared spectral analyzer that measures the change in the carbon isotope (13CO2/12CO2) in carbon dioxide in breath air gas.

During the resting period after taking of the tablet, the bacterium (if present in the stomach) will metabolize the labelled urea and produce labelled carbon dioxide that can be detected in the breath. Detection of isotope-labelled CO2 in exhaled breath indicates that urea in the breath is split. This also means that urease (enzyme used by H. pylori to metabolize urea) is present in the stomach, hence the bacteria are present. Refer to top.

Procedure of test

1. Patient has to breathe into the first sample bag (before taking the UBIT tablet). This bag will be labelled as 'Baseline'.


2. Immediately (within 5 secs), swallow one UBIT tablet on an empty stomach with 100 ml of water. Do not chew, crush or dissolve the tablet.


3. After taking the UBIT tablet, lie down on your left side for 5 min.


4. Remain seated for a further 15 min.


5. 20 min after taking the UBIT tablet, collect breath again using the 2nd sample bag which will be labelled as 'Sample'. The two sample bags will be analysed uisng the machine UBIT-IR300.

Interpretation of results

This is also the reason why a 'pre' and 'post' breath are collected from the patient so that the difference between the pre and post urea measurements can be compared to a cut-off value. Results below the value are assumed to be negative, those above is positive.

That's all.

Sally

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