Are T2 biomarkers of any help in diagnosing asthma

Asthma diagnosis remains a challenging task in routine clinical practice as it is estimated that at least 30% of patients are wrongly diagnosed as being asthmatics. There has been a continuous quest to find biomarkers to help in asthma diagnosis. We conducted a retrospective study on our asthma clinic database and identified 708 patients (58% women) with symptoms suggestive of asthma and naive of any maintenance treatment. Following the GINA recommendations, an asthma was confirmed if reversibility to 400 µg salbutamol was ≥ 12% and 200 ml or if the provocative concentration of inhaled methacholine causing a 20% fall in FEV1 was ≤ 8 mg/ml. Asthma was excluded if both tests were negative. The values of FeNO, blood eosinophil count and total serum IgE as an aid to the diagnosis were assessed by ROC curves and multivariate binary logistic regression. Overall 351 (50%) were considered as asthmatics while 357 (50%) tested twice negative. FeNO yielded an AUC (95%CI) of 0.58 (0.54-0.62) and a threshold of 36 ppb giving 30% sensitivity but 85% specificity. Blood eosinophils yielded an AUC (95%CI) of 0.58 (0.54-0.62) and a threshold of 1.9% giving a 63% sensitivity and a 51% specificity. Total serum IgE yielded an AUC of 0.57 (0.53-0.62) and a threshold of 130 KU/L giving a sensitivity of 41% and a specificity of 77%. After multivariate binary logistic regression, FeNO and blood eosinophils, but not IgE, were found to independently increase the probability of asthma. Moreover, combining the three biomarkers, resulted in an AUC of 0.60 (0.56-0.64). T2 biomarkers fall far from sufficient accuracy to make an asthma diagnosis. Lung function testing remains essential.