INULIN AS A MARKER OF DILUTION OF BRONCHOALVEOLAR LAVAGE IN ASTHMATICAND NORMAL SUBJECTS

Bronchoalveolar ravage (BAL) fluid is a variable mixture of instilled and lung fluid, which makes interpretation of solute concentrations di fficult. We describe the use of inulin as a marker of dilution of BAL in human subjects. BAL, using saline containing 0.1 mM inulin, was saf ely performed in 13 subjects with mild asthma and 11 normal subjects. The dilution factor (DF: inulin concentration in BAL fluid/inulin conc entration in instilled fluid) was measured spectrophotometrically, and it was used to calculate the volume of lung fluid in BAL fluid. There was no significant difference between the median (range) DF of 0.931 (0.825 to 0.952) in asthmatics and 0.907 (0.768 to 0.985) in control s ubjects (p = 0.77). There was wide individual variation in, but no sig nificant difference between, the lung fluid volume of 8.1 ml (5.4 to 2 2.2) in asthmatics and 12.3 ml (1.9 to 30.6) in control subjects (p = 0.56), thus validating comparisons of concentrations per mi of BAL flu id. Alternatively, concentrations can be compared per ml of lung fluid . Inulin fulfilled the requirements for a marker of dilution of BAL, e nabling the validation and standardization of comparisons of solute co ncentrations in BAL fluid.