A comprehensive review of testing for allergies from a major South African pathology laboratory since 2007 shows that health practitioners still have some way to go when it comes to consistently and accurately diagnosing allergies.
That’s the conclusion of Professor Eftyhia Vardas, a medical doctor and clinical virologist who heads up the allergy and immunology laboratory at Lancet Laboratories. Her wide-ranging review of allergy testing including skin prick tests (SPT’s), total IgE and of specific IgE tests (previously known as “radioallergosorbent” test or RAST tests) which detect specific immunoglobulin E (IgE) antibodies that determine which substances individual patients are allergic to. The process of how these tests work differs, skin allergy testing measures the reactions of cells in the skin in response to allergens. Both skin tests and specific IgE allergy tests are useful for the diagnosis of allergy and have different pros and cons, the most important pro for specific IgE tests done on a blood sample is that the patient does not need to stop their antihistamine medications before testing as in the case of skin tests.
She told a mid-November 2019 gathering of ENT surgeons, allergy specialists, paediatricians and general physicians who met under the banner of the South African Allergic Rhinitis Working Group, SAARWG, that the review of allergy testing patterns and positive results, patient demographics and doctors types asking for these tests had evolved into the current testing laboratory diagnostic algorithm for Allergic Rhinitis, (AR).
Diagnostic shortfall
Reviewing the implementation of these recommendations 4 years later, including the costs of allergy tests, her short answer as to whether allergic rhinitis laboratory testing had triumphed diagnostically was a simple ‘no – I don’t think we’re quite there yet’.
While the clinical and economic burden of AR continues to grow in South Africa, lab testing is still marked by confusion, the consensus only recently reached in 2016 – now needs further revision. She said allergy testing was critical for patient management as well as directing appropriate specific pharmacotherapy and immunotherapy. Getting testing for allergies right, also allows early identification of patients that may be at increased risk for development of asthma or severe allergic disease.
Consensus continually evolving
Professor Vardas said that in between 2012-14 the SAARWG set out to audit laboratory-based allergy data to determine if this information could provide regular allergy surveillance, including the regional pollens for South Africa. Over a 5-year period, all allergy tests were reviewed from a single private laboratory, including trends in testing requests, types of doctors ordering allergy tests, patient demographics and seasonal trends in positive results to inform guidelines and testing policy.
The vast majority of both specific IgE tests and skin prick tests (SPT’s) were negative (69%), showing that allergy testing is being applied in patients with a low probability of allergic disease. Selecting the correct patient for allergy testing is therefore very important before embarking on expensive allergy testing. She listed the factors that pointed to successful testing – a high pre-test probability of allergy – as a history of anaphylaxis after exposure to a particular allergen, a history related in time to a particular substance suggesting an allergic reaction, a reliable witness to the reaction and measurable objective signs of an allergic reaction.
The top positive allergens identified, regardless of geographical localisation were dust mites, , followed by grass Plane tree pollen, indoor and outdoor moulds (Altenaria and Cladosporium, Eucalyptus tree pollen and oak tree pollen.
GP’s and Specialists order different types of Allergy tests
GP’s, paediatricians and ENT’s formed the bulk of those ordering allergy tests. But they ordered different types of tests, with GP’s favouring total IgE (t-IgE) as an entry point allergy screen, whereas paediatricians preferred specific IgE (s-IgE) tests and ENT’s used mainly SPT’s. Conclusions drawn from the laboratory allergen data analysis shows that this type of data is a good indicator of prevailing clinical practice, and this information can be used to provide guidance for directed allergy testing and custom-made aero-allergen screens. Prof Vardas emphasised that seasonal variability and geographical pollen audits were not possible via lab data review.
Medical aids out of step
When it comes to costs of allergy tests, although the consensus algorithm for allergic rhinitis adopted in 2016 halved the costs of allergy testing, she said that medical aids appeared to be unaware of and not endorsing hard-won consensus recommendations. She also noted that GP’s seldom indicate to their patients that screening allergy tests with pooled tests necessitates identification of which allergen in the pool is causing positivity, thus making a positive screening test very expensive. Pooled screening tests should therefore be used cautiously, the patient informed of the implications of a positive result which would necessitate further testing to be meaningful clinically. A full 55% of positive Phadiotope and 70% of positive FX5 did not get a breakdown because of cost restriction, which Prof Vardas described as ‘tragic” – these patients have spent money to get a positive pooled result but still don’t know what exactly is causing their allergy. She said t-IgE had thankfully now had been abandoned by paediatricians because it is not an appropriate screening test for allergy, while GP’s however continued to use it.
Further attempts from laboratories to decrease the confusion with allergy testing would mean new revisions to allergy request forms and changes in the recommended consensus based on the new data available.