USING FLOW-CAST TESTING FOR FOOD-ADDITIVE HYPERSENSITIVITY AT A PRIVATE LABORATORY IN SOUTH AFRICA

Introduction: Preservatives are often implicated in allergic diseases such as chronic idiopathic urticaria, angioedema, asthma and anaphylaxis.(1) The current literature reports that reactions to food additives are rare, with proven cases being 0.23% in a large population-based study.(2) The exception is sulphites, which have been shown to exacerbate asthma in a small group of asthmatic patients.(3) An in-vitro tool, the flow cytometric basophil-activation test, is used to assess basophil-activation marker expression following antigen stimulation.(4) It is a very useful test as it can be used in allergic disease where the mechanism is unclear. This is because it detects both IgE-mediated responses and non-IgE mediated hypersensitivity.(4) In this article we examine the frequency with which Flow-CASTS (basophil-activation tests) are ordered by doctors at one of the main private laboratories in South Africa, and how often these tests yield positive results. Methods: During the period 1 June 2017 to 31 May 2019, a retrospective analysis using a purposive sampling method was carried out at a private laboratory. Results: The results showed that of all the tests requested 75% were negative, 16% were positive and 9% were indeterminate. Conclusion: Ear, nose and throat specialists and general practitioners ordered the most Flow-CAST tests, but the tests ordered by general practitioners and paediatricians were more likely to yield a positive result.