Variability in Sputum Sol Phase Proteins in Chronic Obstructive Bronchitis

Abstract
The variability of sputum sol phase proteins was studied in 27 patients with stable chronic obstructive bronchitis. Within individual patients (n ½ 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 alpha1-antitrypsin (α1AT), 32.1%, for alpha1-antichymotrypsin (α1ACh), 26.6%, and for immunoglobulin A (lgA), 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 ½ 84.5%, α1AT ½ 90.1%, α1ACh ½ 58.3%,, and lgA ½ 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 α1 AT (CV from 32.1 to 19.7%) but it had no effect on α1 ACh and lgA. However, although between-patient CV for sputum α1AT was also reduced (from 90.1 to 53.4%, 2 p < 0.01) it significantly increased for α1ACh (from 58.3 to 86.0%, 2 p < 0.05) and lgA (71.6 to 170.1%, 2 p < 0.001), suggesting that such standardization may be inappropriate for these proteins.

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