medwireNews: Researchers have identified four simple clinical criteria that can be used to predict the likelihood of insulin allergy and guide decisions about the need for confirmatory allergy testing.
Although rare, with an estimated prevalence of 0.1–3.0%, “insulin allergy represents a significant complication in diabetes management,” write Agnès Sola-Gazagnes (Assistance Publique-Hôpitaux de Paris, France) and co-authors in Diabetologia.
In order to develop “a rigorous diagnostic and treatment workflow,” the researchers devised four clinical likelihood criteria for insulin sensitivity that included:
- recurrent local or systemic reactions that are either immediate or delayed hypersensitivity;
- reactions provoked by each injection;
- reactions centered on the injection sites; and
- reactions observed by a physician (ie, in response to an insulin challenge test).
The team found that half of 52 individuals with suspected insulin allergy met all four criteria and were therefore categorized as likely to have an insulin allergy. The majority of reactions in this group were local (73%) rather than systemic (27%), and immediate (77%) as opposed to delayed (23%).
In addition, 17% met some criteria and were categorized as possibly having an insulin allergy and 33% met none of the criteria and were classed as unlikely to have an insulin allergy. Just over a third (36.5%) of participants had type 1 diabetes and the remainder had type 2 diabetes.
All of the participants underwent an intradermal reaction (IDR) test, which confirmed a clinical diagnosis of insulin allergy in 92% of those in the likely insulin allergy group, 33% of those in the possible insulin allergy group, and in none of the participants in the unlikely insulin allergy group.
Together, positive clinical likelihood criteria – defined as either likely or possible insulin allergy – identified patients with an IDR-confirmed insulin allergy with a sensitivity of 77% and a specificity of 100%.
Furthermore, the IDR test identified reactions to the index insulin as well as other insulin formulations, but the researchers note that there was “no added value for skin prick and anti-insulin IgE [immunoglobulin E] tests.”
To investigate allergy test diagnostic performance further, they carried out a case–control study among 10 people with clinically likely insulin allergy, 24 who were insulin-treated but non-allergic, and 21 individuals who were insulin-naïve.
The team found that both the IDR and skin prick tests had a specificity and positive predictive value of 100% when clinically likely insulin allergy participants were compared with either non-allergic insulin-treated or insulin-naïve controls.
However, the sensitivity of the IDR test was substantially higher than that for the skin prick test, at 80% versus 10% for both comparisons, while negative predictive values ranged from 90% to 92% for the IDR tests and from 67% to 71% for skin prick tests.
The sensitivity of an in-house IgE test was 50% and specificity was 100%.
Patients with IDR-confirmed insulin allergy were treated using a stepwise strategy that included switching insulin to other antihyperglycemic agents or another insulin, antihistamine treatment, and ultimately switching to continuous subcutaneous insulin infusion, which was needed in 44% of 34 insulin allergic participants.
Sola-Gazagnes et al conclude that the IDR test is “[t]he test of choice to confirm insulin allergy and identify the allergen(s).”
They add: “Only patients classified as clinically likely and possible insulin allergy should undergo confirmatory skin tests.”
medwireNews is an independent medical news service provided by Springer Healthcare Ltd. © 2022 Springer Healthcare Ltd, part of the Springer Nature Group