Investigators have recently examined the predictive value of a composite biomarker strategy using FeNO, blood eosinophils and serum periostin together to predict exacerbation risk in the placebo arms of clinical trials. Investigators propose to examine if this composite biomarker strategy predicts exacerbation risk in patients with asthma on high dose ICS (+/-long-acting beta agonist) treatment and to evaluate the utility of this composite score to facilitate personalised biomarker specific titration of corticosteroid therapy in this population. This study will examine subjects with FeNO<45 ppb and the scoring system will potentially allow identification of a 'low-risk' group who can safely reduce corticosteroid dose. This study will address a second important question of estimating the proportion of patients with severe disease who develop typical (T2)-driven eosinophilic inflammation on progressive corticosteroid withdrawal.