Influx of urea during bronchoalveolar lavage depends on the permeability of the respiratory membrane.

In 6 healthy controls and 23 patients with pulmonary diseases the influx of urea during bronchoalveolar lavage was measured by comparing the concentrations of albumin and urea in the sequential samples recovered. It varied between -28 and 151 mumol/l. In the bronchoalveolar lavage fluid and serum we measured alpha-2-macroglobulin (A2M) and ceruloplasmin (CP). The bronchoalveolar lavage fluid to serum ratios were calculated (QCP and QA2M). QA2M/QCP was taken as a measure of the respiratory membrane permeability; it varied between 0.05 and 0.53. Influx of urea during lavage was higher according as the QA2M/QCP ratio was higher. We conclude that concentrations of substances in the epithelial lining fluid calculated with the urea correction method have to be corrected for the influx of urea.