Saturday, September 15, 2007

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

0503315D

9 comments:

ALsubs said...

hello,sally!!
thanks for your sharing.i have one question. how the sample is stored or send to the lab cos it so special. it is easily gone.

LIU QIAN

we are the XiaoBianTai-7! said...

hi sally,

can i enquire wad will happen if the patient move and not remain seated after the UBIT tablet? besides why do the patient nid to lie on the left side after swallowing the UBIT tablet?

Ai tee
0503160D
TG 01

royal physicians said...

heya girl....wanna ask u...the urea thingy tt person is supposed to swallow is labelled wif uncommon isotope??will it cause any harmful effect 4 the person???coz i thought isotope are pretty dangerous??....

hope u njoy ur SIP girl:).....


nur zahirah tg02

VASTYJ said...

hey.. juz wondering.. why not do a culture or sth.. wun this be a better indicator compared to this test?

Jia Hao

royal physicians said...

Hello!!

Very interesting test indeed =))

Anyway, why cant the patient chew the tablet?

Kangting
0503331A
TG02

BloodBank.MedMic.Haematology said...

Hello

Can i know is there anything contains in the sample bag that will keep the breath in good condition? (e.g blood tube contain anticoagulant to prevent clotting). Thanks

Ci Liang
TG01

ALsubs said...

hey gal..
why muz the patient lie down first then change into sitting position after 5 mins ah?

Shu Hui
TG02

Vino said...

HEY hi SALLy

I think most of us have the same question.. why issit that the patient must lie down on the left side and then sit uprite for another 15 mins?? Issit smth to do with the heart?? THe tablet( dissolved in the blood) should go to the heart first before it gets into the lungS? am not sure..

Vinodhini
TGO2

Star team said...

Hey Sally,

When expiring the air into the bag, is there a seal or something to prevent any air to escape or mix with the surrounding air? Wouldnt it produce inaccurate results?

Martin
TG02