Measuring plasma exudation in nasal lavage fluid and in induced sputum as a tool for studying respiratory tract inflammation.

We performed nasal lavage (NAL) combined with induced sputum to determine exudative inflammation in the upper and lower airways in patients with chronic sinusitis and in controls. To monitor plasma exudation into the respiratory lumen and loss of size-selectivity of the mucosa, we determined the sample-to-serum ratio of albumin and alpha-2-macroglobulin, Qa1b and Qa2m, and the dilution independent Relative Coefficient of Excretion, RCE=Qa2m/Qa1b. To detect low protein levels in NAL and induced sputum we adapted an ELISA system for alpha-2-macroglobulin described by Out et al. [Clin. Chim. Acta, 165 (1987) 277-288], and modified this into a sensitive ELISA for albumin. Dithiothreitol, added to increase sputum solubility, did not interfere with the analysis, nor did N-ethylmaleimide, added to block dithiothreitol. In this study plasma exudation in induced sputum is significantly increased in patients with chronic sinusitis, compared to controls. Plasma exudation in NAL is also increased in patients, although not significant. The RCE in NAL and sputum is well-correlated in one of the three study visits. There is much variation in sample protein-levels partly due to differences in dilution and the heterogeneity of the studied population. Determination of plasma exudation together with RCE in NAL and induced sputum is a good, non-invasive way to quantify inflammation of airway mucosa.