POSTN and allergic asthma: Similarly, in severe allergic asthma patients after 48 weeks of omalizumab, the EXTRA study also demonstrated that the reductions in protocol-defined exacerbations were greater in the baseline level of the higher blood Eos subgroup (≥260 cells/μL), higher serum periostin subgroup (≥50 ng/mL) or higher fractional exhaled nitric oxide subgroup (≥19.5 ppb).35