A comparison of albumin and urea as reference markers in bronchoalveolar lavage fluid from patients with interstitial lung disease.

Lavage fluids were investigated for 67 subjects in 6 groups: 12 with active sarcoidosis, 8 with inactive sarcoidosis, 17 with pigeon breeder's disease, 10 asymptomatic pigeon breeders, 12 with idiopathic pulmonary fibrosis (IPF) and 8 normal subjects. Albumin and urea per ml of bronchoalveolar lavage fluid (BALF) were determined for each subject together with percentage return of fluid (BAL%). Novel assay systems were employed to measure urea and albumin and these were compared with existing analytical techniques. When compared with the control group, we found that urea per ml of BALF was not statistically different for all other groups, except those with pigeon breeder's disease who had significantly raised levels. For albumin, however, three groups had significantly higher levels than the controls, namely those with active sarcoidosis, pigeon breeder's disease and IPF. BAL% return showed no significant differences for any group when compared with the controls. We conclude that since albumin is significantly raised in most patients with interstitial lung disease it does not represent a suitable marker for the quantitation of reactive proteins in BALF. Urea shows much less variability between groups than does albumin, and hence in the absence of a proven alternative represents the most reliable estimate available of epithelial lining fluid dilution during the lavage procedure, providing dwell time is kept to a minimum.