Quantitative BAL: a suitable method for the assessment of epithelial lining fluid in alpha-1 antitrypsin deficiency?

Abstract

Measurements on biological fluids form the mainstay of routine clinical investigations. Samples of blood, urine, etc are, generally, easily obtainable and measurements can be interpreted directly. On the other hand, alveolar epithelial lining fluid (ELF) is relatively inaccessible but offers valuable insight into pathogenesis and pharmacokinetics relating to diseases affecting the alveolus. The lung is frequently described as having the surface area of a tennis court. When folded up to fit into the volume of an average thorax, it creates a complex maze that represents a significant obstacle to accessing ELF. The difficulty of gaining access safely and without disrupting the alveolar milieu is complicated by the delicate structure and function of the gas exchange membrane. Different approaches have been adopted including the use of a bronchoscopic microsample (PMS) probe,1 which allows direct measurements from ELF, or bronchoalveolar lavage (BAL), which requires a correction method to adjust for the dilutional effects of the lavage fluid. Urea (or albumin or creatinine) has been commonly used as an endogenous marker to estimate the volume of ELF2–5: by measuring the urea in BAL aspirate and plasma, a ratio can be calculated allowing an estimate of the dilution of apparent volume of ELF. ‘Contamination’ from lavage of the larger airways is also an issue that is influenced by the method of BAL sampling. This is not particularly important in routine clinical BAL, and guidelines do not stipulate the order of …