Baseline Composite Score for 12-Month Clinical Remission in Biologic-Treated Severe Asthma: Development of the Base4Score

Background: Clinical remission has become a realistic treatment goal in severe asthma, but current evidence mostly reports global remission rates without accounting for baseline disease burden. No simple tool exists to quantify baseline severity and estimate an individual patient’s probability of achieving remission under biologic therapy. Methods: This prospective observational study included 93 adults with severe asthma initiating tezepelumab across 14 specialised severe asthma units in Spain. Four baseline domains—poor symptom control (ACT < 20), ≥1 severe exacerbation in the previous 12 months, maintenance oral corticosteroid (OCS) use, and FEV1 < 80% predicted—were used to construct an empirically weighted composite score (Base4Score) based on the inverse probability of correcting each abnormal domain at 12 months. Strict clinical remission at 12 months was defined as ACT ≥ 20, no severe exacerbations, no maintenance OCS, and FEV1 ≥ 80%. Logistic regression was used to assess the association between the score and non-remission, adjusting for age, sex, smoking status, T2 phenotype, and biologic-naive status. Results: Of 93 treated patients, 81 had complete baseline data for Base4Score derivation and 77 had complete 12-month data for strict clinical remission analysis. Strict clinical remission was achieved in 16/77 patients (20.8%). Remission rates decreased across increasing baseline score strata: 40.0% for scores < 5, 17.6% for scores 5 to <9, and 12.5% for scores ≥ 9 (linear p-trend = 0.022). Each 1-point increase in the continuous Base4Score was associated with higher adjusted odds of non-remission (OR 1.22; 95% CI 1.00–1.49; p = 0.047), and patients with scores ≥ 9 had approximately sevenfold higher adjusted odds of non-remission than those with scores < 5 (OR 6.77; 95% CI 1.40–32.84; p = 0.018). Conclusions: The Base4Score is a simple, empirically derived baseline severity index that predicts 12-month strict clinical remission in severe asthma treated with tezepelumab. If externally validated, it could help personalise expectations, optimise timing of biologic initiation and guide treat-to-target strategies in severe asthma.