EVALUATION OF ALBUMIN AS A REFERENCE MARKER OF DILUTION IN BRONCHOALVEOLAR LAVAGE FLUID FROM ASTHMATIC AND CONTROL SUBJECTS

Background-Standardised expression of results of bronchoalveolar lavag e (BAL) is problematical in the absence of a validated ''denominator'' of epithelial lining fluid dilution. The suitability of albumin in BA L fluid has been investigated in groups of clinically stable asthmatic and control subjects. Methods-Absolute levels of albumin in BAL fluid were measured in a preliminary study of 21 asthmatic and 10 control s ubjects. In a more complex study designed to investigate the origin of albumin sampled at BAL in nine asthmatic and seven control subjects, radiolabelled albumin was injected intravenously five minutes before B AL. Results-In the preliminary study levels of albumin in BAL fluid we re very similar, with a geometric mean value of 44 (95% CI 35-54) mug/ nil BAL supernatant for the asthmatic subjects and 41 (95% CI 33-52) m ug/ml for the controls. The majority of control and asthmatic subjects in the radiolabel study exhibited minimal flux of albumin from the ci rculation into the BAL aspirate. This finding was not uniform, however , and in a third of the asthmatic subjects an albumin flux equivalent to >20% of the measurable albumin was found in two or more aliquots of a 3 x 60 ml lavage. Conclusions-The results of this investigation int o the source of albumin sampled at BAL suggest that, in general, album in would be a reasonable reference solute for normalising the degree o f dilution of BAL fluid in the groups studied. The origin of albumin w as not always restricted to the bronchopulmonary segment under investi gation, however, with significant leakage from the blood compartment i n some individuals despite the consistency of absolute levels observed in the preliminary study.