Careful history
taking and observation of food-related
reactions may indicate the source of
food intolerance.
The food history should include:
- Identification of suspect food,
drink, sweets / candy, or chewing gum.
- What is the time lag between eating
and development of symptoms?
- What types of symptoms ensue?
- What amount of food is required to
cause reaction?
- Does the reaction occur with every
ingestion of the food?
- Does the reaction only occur under
certain circumstances, e.g. exercise or
stress?
- When did the last reaction occur?
- Do allergies exist, e.g. hay fever,
asthma, eczema?
- Do other family members have food
reactions, if so, which?
Breath tests
Breath tests are the most useful and
non-invasive tests for determining the
various sugar (e.g. fructose, lactose,
sucrose) and sugar alcohol (e.g.
sorbitol, xylitol) intolerances. They
are well validated, widely used, but
some discussion still exists about the
ideal test conditions. These tests
should not be used in infants and
reduced doses of test compound are used
in children. The tests procedures are
identical for all the intolerances (See
Patient breath test preparation form,
Breath test analysis form,
Symptom score form,Test
site locations). Following are important details regarding the test procedure.
- Dietary restrictions, no smoking or
excessive exercise from the day before
testing and no antibiotics or
colonoscopy in the last week pre-test.
- Ingestion of a specific amount of
the sugar or sugar alcohol to be tested
for intolerance.
- Regular breath samples taken for a
standardized period (at clinic or at
home).
- Diary of symptoms during the next
day for calculation of the symptom
index.
- Measurement of specific gases, e.g.
hydrogen and methane, in the breath
samples.
An intolerance is diagnosed based on the
symptoms following the test and the gas
concentrations in the breath samples.
The diagnosis is confirmed by a
significant decrease in symptoms whilst
on a diet low in the poorly tolerated
sugar or sugar alcohol. Expert dietary
advice is very helpful for the
identification of food and drink
containing the difficult-to-spot
offending ingredient. Examples of such
ingredients are so-called hidden lactose
or fructans in vegetables or whole-meal
products (See
Food tables).
Direct enzyme quantification in tissue
biopsies
Direct enzyme levels can be determined
in biopsies of the small intestine.
However, this test is invasive,
expensive and performed by only a few
laboratories. Sucrase-isomaltase
deficiency, a quite rare genetic
disorder, is preferentially diagnosed
using this method.
Genetic tests
Genetic testing is available for some of
the sugar intolerances.
Lactose
intolerance: the severest genetic
form of intolerance (CC13910 / GG22018
i.e. homozygotes) can be very reliably
diagnosed using a simple genetic test
with cells taken, for example, from the
inside of the cheek. The breath test is
abnormal in all these individuals. Those
with an intermediate genetic form of
intolerance (CT13910 / GA22018 i.e.
heterozygotes), which are the majority
of individuals, have a wide range of
intolerance severity to lactose. This is
most usefully assessed using the breath
test measuring the actual effect of
lactose ingestion. Even a sizeable
percentage of individuals without the
genetic signature of intolerance
(TT13910 / AA22018) have lactose
intolerance. In summary, breath testing
is overall the most useful form of
testing. Genetic testing reliably
identifies a proportion of severely
affected individuals and is also useful
in screening larger numbers of
individuals or relatives of patients
(See
Test site locations).
Fructose
intolerance due to malabsorption (common
fructose intolerance):
no specific genetic test is currently
available. Testing is by breath test
(See
Test
site locations).
Hereditary
fructose intolerance (HFI): about
70% of genetic aberrations
(polymorphisms) associated with HFI can
currently be identified and these should
be determined in case of clinical
suspicion, due to the lifelong and
possibly severe consequences of not
excluding fructose meticulously from the
diet (See
Test site locations).
Sucrase-isomaltase deficiency (sucrose - starch intolerance): genetic
analysis from duodenal biopsies is not widely available, but has demonstrated
several genetic polymorphisms, i.e. abnormalities.
Sorbitol and
xylitol intolerance: no specific
genetic tests are currently available.
Testing is by breath test (See
Test site locations).
Other tests: stool, blood
Various stool tests, including pH tests, have
been used, but they should no longer be
advocated except for testing in infants.
Measurement of blood glucose following
ingestion of lactose (lactose tolerance
test) is less specific than breath
testing and is susceptible to more
interference. Use of this test is
diminishing and should be discouraged.