Food Allergy - Establishing the Diagnosis
As gastrointestinal symptoms are non-specific, other potential causes should be excluded before considering the possibility of food intolerance.
The stools should be examined, especially for protozoa such as Giardia.
A full blood count and determination of the serum albumin, acute-phase proteins, and endomysial antibodies helps to exclude inflammatory bowel disease and coeliac disease.
Patients with diarrhoea should have a flexible sigmoidoscopy and, if over the age of 40 years, a barium enema or colonoscopy.
Psychological disorders such as anxiety and clinical depression should also be excluded; for example, chronic hyperventilation leads to abdominal pain, flatulence, and bloating but rarely causes diarrhea, and characteristically these patients easily become breathless with chest pain, palpitations, dizziness, and sometimes full-blown panic attacks.
The identification of patients with psychological problems leading to gut symptoms still depends on clinical assessment.
There is considerable overlap between symptoms caused by food intolerance and those due to irritable bowel syndrome.
No objective test can separate these conditions.
Patients with chronic diarrhea, abdominal bloating, excess rectal flatulence or, occasionally, resistant constipation are most likely to suffer from food intolerance.
However, food intolerance can occasionally be responsible for stubborn cases of constipation.
The possibility of food intolerance should therefore be considered in every patient with apparent irritable bowel syndrome.
It may be helpful to determine the serum IgE concentration in patients with anaphylaxis or rapid onset of symptoms - especially if these are associated with wheezing, itching or urticaria.
Elevated levels should prompt a search for specific allergens by means of skin-prick or radioallergoabsorbent (RAST) testing.
In patients with chronic gastrointestinal symptoms, IgE concentrations are usually normal and skin prick and RAST testing unhelpful.
Experience suggests that examination of a food diary is also of limited value as the foods most likely to produce intolerance are those which are usually eaten daily.
Exclusion from the diet of one food at a time is rarely successful as many patients are upset by several.
A number of commercial techniques for identifying allergy are advertised, including hair and blood analysis and the 'Vega' machine, although there is no evidence as to their reliability.
The stools should be examined, especially for protozoa such as Giardia.
A full blood count and determination of the serum albumin, acute-phase proteins, and endomysial antibodies helps to exclude inflammatory bowel disease and coeliac disease.
Patients with diarrhoea should have a flexible sigmoidoscopy and, if over the age of 40 years, a barium enema or colonoscopy.
Psychological disorders such as anxiety and clinical depression should also be excluded; for example, chronic hyperventilation leads to abdominal pain, flatulence, and bloating but rarely causes diarrhea, and characteristically these patients easily become breathless with chest pain, palpitations, dizziness, and sometimes full-blown panic attacks.
The identification of patients with psychological problems leading to gut symptoms still depends on clinical assessment.
There is considerable overlap between symptoms caused by food intolerance and those due to irritable bowel syndrome.
No objective test can separate these conditions.
Patients with chronic diarrhea, abdominal bloating, excess rectal flatulence or, occasionally, resistant constipation are most likely to suffer from food intolerance.
However, food intolerance can occasionally be responsible for stubborn cases of constipation.
The possibility of food intolerance should therefore be considered in every patient with apparent irritable bowel syndrome.
It may be helpful to determine the serum IgE concentration in patients with anaphylaxis or rapid onset of symptoms - especially if these are associated with wheezing, itching or urticaria.
Elevated levels should prompt a search for specific allergens by means of skin-prick or radioallergoabsorbent (RAST) testing.
In patients with chronic gastrointestinal symptoms, IgE concentrations are usually normal and skin prick and RAST testing unhelpful.
Experience suggests that examination of a food diary is also of limited value as the foods most likely to produce intolerance are those which are usually eaten daily.
Exclusion from the diet of one food at a time is rarely successful as many patients are upset by several.
A number of commercial techniques for identifying allergy are advertised, including hair and blood analysis and the 'Vega' machine, although there is no evidence as to their reliability.
