Continuing Medical Education
Diagnosis of food allergy: History, examination and in vivo and in vitro tests
One cannot depend on one single test to diagnose food allergy. A detailed history is an essential initial step in cases of suspected food allergy. Aspects of the history should be gathered separately for each food being considered, as a patient may experience different types of reactions with various foods, each of which requires individual diagnostic and management strategies. History alone is not diagnosticand additional measures of sensitisation or food challenges are often required.
In suspected immunoglobulin E (IgE)-mediated allergy, skin-prick tests (SPTs) and/or measurement of serum specific IgE antibodies (ImmunoCAP) to suspected foods is used to prove sensitisation. Sensitisation does not, however, confirm clinical food allergy as these tests indicate an immunological response to the specific allergen, but the diagnosis requires a clear correlation between the test result and clinical reaction (by positive history or food challenge). The magnitude of the test result (SPT mean wheal size or ImmunoCAP level in kU/L) correlates with the likelihood of clinical allergy, but not the severity of a reaction.
Choice of the allergens tested should be guided by the history, but limited to the lowest necessary number to avoid false-positive results. Tests for sensitisation to foods should not be performed when the history indicates that such foods are tolerated. Ninety-five per cent positive predictive values (where a clinical reaction can be predicted in 95% of cases) have been described for immediate reactions, but may be population specific.
There are no validated tests to confirm non-IgE- or mixed IgE- and non-IgE-mediated food allergies. Diagnosis of this group of allergies depends on elimination of the suspected food, clearance of symptoms, and recurrence of symptoms on re-introduction of the food.
D A van der Spuy, Private Practice, Cape Town, South Africa
A J Terblanche, Department of Paediatrics, Faculty of Health Sciences, University of Pretoria and Steve Biko Academic Hospital, Pretoria, South Africa
S Karabus, Private Practice, Christiaan Barnard Memorial Hospital, Cape Town, and Division of Allergy, Department of Paediatrics and Child Health, Faculty of Health Sciences, University of Cape Town and Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
M Kriel, Private Practice, Alberton, Johannesburg, South Africa
A I Manjra, Private Practice, Westville, Durban, South Africa
E Goddard, Division of Paediatric Gastroenterology, Department of Paediatrics and Child Health, Faculty of Health Sciences, University of Cape Town and Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
C L Gray, Private Practice, Vincent Pallotti Hospital, Pinelands, Cape Town, South Africa
A C Lang, Wits Donald Gordon Medical Centre, Johannesburg, South Africa
S M Risenga, Department of Pulmonology and Allergy, Faculty of Health Sciences, Polokwane Campus, University of Limpopo, Polokwane, South Africa
M E Levin, Division of Allergy, Department of Paediatrics and Child Health, Faculty of Health Sciences, University of Cape Town and Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
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Date published: 2014-11-24
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