General anesthetic allergy testing

Threshold for basophil activation test positivity in neuromuscular blocking agents hypersensitivity reactions

Background

Several different criteria for the positivity of the flow-assisted Basophil Activation Test (BAT) for the diagnosis of Neuromuscular Blocking Agents (NMBA) hypersensitivity reactions have been used in past studies. Our aims were to determine the threshold for BAT positivity expressed as the stimulation index (SI, calculated as the percentage of activated basophils after stimulation with NMBA divided by the number of basophils with no NMBA stimulation) and as the percentage of activated basophils, and to determine the sensitivity and specificity of BAT for NMBAs.

Methods

22 consenting adult patients with previous intraanaesthetic NMBAs-related hypersensitivity reactions were tested for the culprit drug. 34 controls who tolerated NMBAs were similarly tested. BAT was performed using Flow2Cast technique and the up-regulation of the CD63 marker on the basophils was measured using Cell Quest programme (FACSCalibur Becton Dickinson, USA). Receiver operating characteristics curve (ROC) analysis was performed.

Results

ROC curve analysis for BAT results versus history yields a stimulation index of 1.76 as the optimal threshold, with an AUC of 0.81 (CI 95% 0.69-0.93, p < 0.01) and a percentage of activated basophils > 5.01%, with an AUC of 0.84 (CI 95% 0.72-0.95, p < 0.01). Considering both thresholds (the SI ≥ 1.76 together with the percentage of activated basophils > 5%) as diagnostic criteria, 15 patients had positive BAT, the overall BAT sensitivity being 68.18% (CI 95% 45.11-82.26%). None of the controls fulfilled both criteria and the specificity of the test was 100% (CI 95% 87.35-100%).

Conclusions

With a stimulation index ≥ 1.76 and a percentage of activated basophils > 5.01% as threshold, the performance of BAT for NMBAs yields 68.18% sensitivity and 100% specificity.

Threshold for positivity and optimal dipyrone concentration in flow cytometry-assisted basophil activation test

Purpose

Basophil activation occurs both in patients with immediate hypersensitivity reactions to anti-inflammatory drugs and in healthy controls in a dose-dependent manner. Our aims were to define the optimal basophil activation test (BAT) concentration and the threshold for BAT positivity for dipyrone.

Methods

From 45 patients with a positive history of an immediate hypersensitivity reaction to dipyrone, we found 20 patients with dipyrone-induced anaphylaxis demonstrating positive skin tests. All selected patients, as well as 10 healthy controls, were tested in vivo and in vitro. BAT was performed using Flow 2CAST technique with three low dipyrone concentrations: 25 µg/mL (c1), 2.5 µg/mL (c2) and 0.25 µg/mL (c3). The threshold for BAT positivity was established using receiver operating characteristics (ROC) curve analysis.

Results

Using ROC curve analysis the highest area under curve, 0.79 (0.63-0.95) (P<0.01), was found for c3. When the highest stimulation indexes from the three concentrations for each patient were used, ROC curve analysis revealed an area under curve of 0.81 (0.65-0.96) (P<0.01), sensitivity and specificity were 0.70 and 1 and the optimal threshold value for BAT positivity was 1.71. Thirteen patients had a positive BAT for at least one of the tested dipyrone concentrations. All healthy controls presented negative BAT.

Conclusions

BAT might be a useful technique to diagnose dipyrone allergy, provided all three low dipyrone concentrations are used together. With an assay-specific threshold of 1.71, ROC curve analysis yields 70% sensitivity and 100% specificity.

Is a positive history of non-anaesthetic drug allergy a predictive factor for positive allergy tests to anaesthetics?

AIMS

International recommendations stipulate not performing screening skin tests to a drug in the absence of a clinical history consistent with that specific drug allergy. Nevertheless, two publications showed that a positive history of non-anaesthetic drug allergy was the only predictive factor for a positive skin test when screening for allergy to anaesthetic drugs was done. We selected from a surgical population 40 volunteers with a prior history of allergy to non-anaesthetic drugs in order to analyse the prevalence of positive allergy tests to anaesthetics.

METHODS

The selected adult patients were tested for 11 anaesthetic drugs using in vivo tests: skin prick (SPT) and intradermal (IDT) tests and in vitro tests: the basophil activation test (BAT) and detection of drug-specific immunoglobulin E (IgE).

RESULTS

The prevalence for the positive SPT and IDT was 1.6% and 5.8% respectively. The result of flow cytometry agreed with the SPT in five out of seven positive SPT (71%). IgEs confirmed two positive SPT with corresponding positive BAT. Ten per cent of the patients had a positive prick test to neuromuscular blocking agents (NMBA). For midazolam none of the SPT was positive, but 11 patients had positive IDT nonconfirmed by BAT.

CONCLUSION

The prevalence of positive in vivo and in vitro allergy tests to NMBAs is higher in our study population. This could be an argument for pre-operative SPT to NMBAs for the surgical population with reported non-anaesthetic drug allergies. A larger prospective study is needed to validate changes in clinical practice.