SERPINA1 and alpha 1-antitrypsin deficiency: A study of 193 patients with AATD evaluated nitrogen washout, a sensitive method for identifying small airway disease, and showed that the lung clearance index was abnormal in 83% of the patients with the Pi*ZZ genotype, in 47% of those with other genotypes, and in 43% of the 117 patients with normal FEV1.43