More detailed information on patient preparation :
A.
4 weeks before the test
:
Arrange
the appointment to be at least 4 weeks from the date of antibiotic
discontinuation.
However, if the
antibiotic is prescribed for long term use, patient should talk to their doctor
to see if it can be withheld prior to the test.
If it cannot be withheld, the test can still be performed but the
nature, dose and frequency of the antibiotic must be properly documented
on the request form to aid result interpretation.
B.
At least 1 week before
the test:
- avoid the use of prokinetic drugs
or laxatives including lactulose
- if investigating lactose
malabsorption; avoid high lactose food e.g. milk products
- any acute diarrhoeal illness has
to be settled, otherwise postpone the test
C. The evening before the test:
1. Evening meal:
prefer cooked white rice as staple food. Avoid bread, pasta, pizza, fibre
cereals, wheat and oat containing food, beans, peas, potato, and corn.
Meat like fish, chicken, beef, pork or lamb are acceptable.
Avoid canned or packet soups and sauces. If investigating for
fructose malabsorption,
avoid fruit and fruit juices.
2. Fasting after the evening meal
(plain water is allowed during the fasting and during the test):
- Adults and children more than 4 years, start fasting after 8pm (i.e.
evening
meal should be finished latest by 8pm
)
- Children between 1 to 4 years old - fast for a minimum of 8 hours, i.e. start
fasting at 12 MN.
- Babies up to 12 months old - fast for a minimum of 3 hours.
D. The morning of the test:
Avoid use of tooth paste while
brushing teeth. Mouthwash for rinsing is allowed. Avoid cigarette smoking
and strenuous physical exercise.
Assay Method
Principle:
Gas chromatography
Reagent:
In-house reagents
Analyser:
Quintron Breath Tracker
Diagnostic Use and Interpretation
The test:
After an overnight fast, hydrogen and methane are simultaneously measured from expired breaths at baseline. Then a fixed oral dose of selected carbohydrate is given, followed by measurement of the 2 gases every 30mins for a total of 2 to 3 hours. The baseline gases concentration and the magnitude of rise in relation to time to peak/plateau will be interpreted in light of the type and dose of carbohydrate used and the pre-test diagnostic question.
Interpretation :
Depending on the trade off between sensitivity and specificity for different pre-test probabilities/indications, the criteria for positivity in breath hydrogen/methane test varies widely. Cut points can also differ with the type and dose of substrates used.
Test generally considered as positive (provided timing of the peak occurred as expected) if :
Hydrogen:
More than 20ppm above baseline;
or, 2 or more consecutive readings more than 10ppm above baseline
Methane:
More than 20ppm above baseline; or methane level more than 2 times above baseline
Less stringent criteria than the above can be considered in selected cases to improve sensitivity.
In high methane producers, combined consideration of both hydrogen and methane response may improve diagnostic sensitivity.
Limitations of the test:
1. Concurrent presence of fast bowel transit time, small bowel bacterial overgrowth or bacterial activity in mouth food residues can cause false positivity when the test is intended for detection of carbohydrate malabsorption.
2. False negative or blunted hydrogen response can occur in non-hydrogen producers. Simultaneous measurement of methane can help to identify these subjects.
3. If the patient has been on antibiotics recently, the hydrogen response can be unpredictable ? both exaggeration or attenuation are possible.
4. Hyperventilation e.g. from strenuous exercise or hypoventilation e.g. from children sleeping immediately before or during the test can cause spurious breath readings. Simultaneous measurement of expired carbon dioxide can correct for these variations.
5. This test requires some degree of patient co-operation. Sometimes it is not possible to collect quality breaths from very young or agitated children
6. Lactulose, as one of the substrates used in breath test for small bowel bacterial overgrowth, by itself can induce acceleration in bowel transit time in a dose dependent manner. Interpretation need to take this effect into account.
Diagnostic use
Non-invasive detection of (i)
carbohydrate malabsorption
(ii)
small intestinal bacterial overgrowth
. Diagnosis of these conditions also depends on other investigations including duodenal/jejunal biopsy, jejunal fluid culture, genetic testing and therapeutic trial. (iii) The test may also give an indication of oro-caecal transit time (more commonly used in the research setting).
Carbohydrate malabsorption
Normally with sufficient disaccharidase activity along small bowel mucosal lining and with adequate small bowel absorptive area, ingested disaccharides like lactose or sucrose are completely hydrolysed and absorbed as monosaccharides like fructose, glucose or galactose. No rise in hydrogen or methane is expected. However, if the small bowel enzyme activity and/or absorptive area become inadequate (e.g. from lactase deficiency or from generalised gut diseases like e.g. coeliac or Crohns), the unabsorbed lactose will go down to the colon where it undergoes bacterial fermentation with gases released. Part of the hydrogen from hydrogen producers and/or methane from 'non-hydrogen producers' will be absorbed and expired through lungs, causing an observed rise in hydrogen/methane concentration after about 90-120mins - the usual oro-caecal transit time.
While carbohydrate malabsorption can be diagnosed from the above breath test, its correlation with carbohydrate intolerance symptoms like nausea, bloating, abdominal pain and diarrhoea is not straightforward. The correlation between these 2 entities (carbohydrate malabsorption and carbohydrate intolerance) depends on factors like : nature and dose of carbohydrate used in the test in relation to the individual intake practice in real life environment; co-intake of carbohydrate absorption enhancers or inhibitors; proneness of individual bowel towards heightened sympathetic response from volume distension; presence of sulphate reducing bacteria with H
2
S production causing direct toxic effect on gut; unabsorbed luminal carbohydrate's osmotic effect or altered signalling mechanism causing diarrhoea etc. Constipation is more common in high methane producers.
Small bowel bacterial overgrowth
Glucose as a monosaccharide normally is completely absorbed in the proximal small bowel. Thus, it is usually unavailable to colonic bacteria for fermentation to release hydrogen. However, if there is a significant small bowel bacterial overgrowth or rapid bowel transit, the ingested glucose can be fermented in the small bowel to release gases, registered as a peak during monitoring.
In contrast, lactulose as a synthetic disaccharide is normally not metabolised nor absorbed in the small bowel. Thus a late appearance of a colonic peak from colonic bacteria with hydrogen release is to be expected. However, in small bowel bacterial overgrowth, lactulose will be prematurely exposed to the small bowel bacteria, thus an early abnormal small intestinal hydrogen peak can be observed usually before 90 minutes (assuming normal bowel transit time).
We believe Glucose overall is a better substrate than Lactulose for small bowel bacterial overgrowth (at least for proximal small bowel). As of 3/9/2012, for all lactulose request s, glucose will be used instead. Lactulose will only be used after prior discussion with and approval by Chemical Pathologist on duty.
High fasting baseline hydrogen / methane values:
This finding can be a result of consumption of poorly absorbable complex carbohydrates like potato, in the evening before the test. It can also be caused by small bowel bacterial overgrowth, or untreated celiac disease where there is enhanced exudation and prolonged fermentation of endogenous glycoprotein / exogenous carbohydrates. On the contrary, high fasting methane in methane producers normally is derived from endogenous rather than dietary substrates.
Contact Information
Emails to
chemicalpathologist@adhb.govt.nz
will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via
Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours
: contact
Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad
(Clinical Lead)
:
SamarinaM@adhb.govt.nz
ext. 22402
Dr Cam Kyle:
CampbellK@adhb.govt.nz
ext 22052
Dr Weldon Chiu:
WeldonC@adhb.govt.nz
ext. 23427
Dr Campbell Heron:
CHeron@adhb.govt.nz
ext. 23427