Variability in sputum sol phase proteins in chronic obstructive bronchitis. The value of using albumin for standardization.

The variability of sputum sol phase proteins was studied in 27 patients with stable chronic obstructive bronchitis. Within individual patients (n 1/2 11), variability over 5 consecutive days was similar for each of 4 proteins studied: average coefficient of variation (CV) for albumin was 39.8% for alpha 1-antitrypsin (alpha 1AT), 32.1%, for alpha 1-antichymotrypsin (alpha 1ACh), 26.6%, and for immunoglobulin A (IgA), 35.1%. The calculation of sputum-to-serum ratios did not affect this variability. Between patients (all patients studied on a single day) the variability of sputum sol phase proteins was greater (CV: albumin 1/2 84.5%, alpha 1AT 1/2 90.1%, alpha 1ACh 1/2 58.3%, and IgA 1/2 71.6%) and was also unaffected by the use of sputum-to-serum concentration ratios. "Standardization" for albumin reduced the average within-patient variability for sputum alpha 1AT (CV from 32.1 to 19.7%) but it had no effect on alpha 1ACh and IgA. However, although between-patient CV for sputum alpha 1AT was also reduced (from 90.1 to 53.4%, 2 p less than 0.01) it significantly increased for alpha 1ACh (from 58.3 to 86.0%, 2 p less than 0.05) and IgA (71.6 to 170.1%, 2 p less than 0.001), suggesting that such standardization may be inappropriate for these proteins.