Limitations of Using Urea to Quantify Epithelial Lining Fluid Recovered by Bronchoalveolar Lavage^1–3

Abstract

The quantitation of substances in the epithelial lining fluid (ELF) of the lower respiratory tract, as obtained by bronchoalveolar lavage (BAL), is not precise because of the variable dilution of the ELF by the instilled lavage fluid. It has been reported that the absolute concentration of proteins in ELF can be determined by using the ratio of urea concentration in BAL fluid to that in serum as a method to calculate the volume of ELF recovered by BAL. Furthermore, it has been suggested that the error caused by diffusion of urea into the instilled lavage fluid can be minimized by instilling only 100 ml (5 X 20 ml) of saline rather than 300 ml (6 X 50 ml). We tested the validity of this method by collecting and individually analyzing aliquots from 2 different BAL protocols--a 100-ml (5 X 20 ml) BAL and a 300-ml (6 X 50 ml) BAL--performed in 6 healthy, nonsmoking subjects. Total protein, albumin, and urea were measured in each aliquot and in pooled fluid from each BAL procedure, and urea was measured in serum. In the 300-ml BAL, total protein and albumin concentrations tended to decrease progressively from the second to the sixth aliquots. In contrast, the urea concentration increased progressively from the first to the sixth aliquots. The concentration of albumin in ELF, calculated from the concentration of urea and albumin in each BAL aliquot, tended to decrease in each successive aliquot, becoming significant by the fourth aliquot.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of interleukin-6 in bronchoalveolar lavage fluid by radioimmunoassay: differences between patients with interstitial lung disease and control subjects

“…Variation in albumin and urea in BALF have been reported previously (Jones et al, 1990) as have the limitations of both these substanees to accurately reflect dilution effeets in BALF (Rennarde/o/., 1986;Marcy et at., 1987). In the absence of any reliable alternative, however, we felt it necessary to quote values using both.…”

“…Bronchoalveolar lavage was performed using 180 ml of bicarbonate-bufTered saline, pH 7-4, at 37°C, The right middle lobe was the lavage site chosen for each subject in the study, A lavage volume of more than 120 ml was chosen to ensure adequate alveolar sampling (Kelly et at., 1987), all lavage procedures were completed within 4 min in order to reduce passive diffusion of urea (Marcy et al, 1987), The lavage fluid was filtered through a single layer of sterile gauze to remove gross contamination. The cellular component was removed by centrifugation at 400 i' for 10 min and supernatants were stored at -70°C within 90 min of sample collection prior to assay (up to 6 months).…”

“…Four groups were studied: sarcoidosis; pigeon breeders' disease (PBD); asymptomatic pigeon breeders; and idiopathic pulmonary fibrosis (IPF); a control group was also studied. IL-6 levels in BALF were standardized by means of urea in serum and BALF to give concentrations of IL-6 per ml of epithelial lining fluid (ELF) and also by reference to albumin, since controversy exists as to which of these substanees provides the most suitable reference marker (Rennard et al, 1986;Marcy et al, 1987).…”

Bronchoalveolar lavage in children

“…The two substances which have been used in a number of studies as denominators for other BAL fluid constituents are urea and albumen [22,40,41]. Urea is thought to be present in equal concentrations in serum and ELF and would therefore potentially be a helpful reference substance for BAL fluid.…”

Comparison of inulin with urea as dilutional markers of bronchoalveolar lavage in healthy and heaves-affected horses

“…the time lavage fluid remains in the airways before being re-aspirated, is a cornerstone in the standardisation of the bronchoalveolar lavage technique. With increasing dwell time, BALF urea concentration increases and consequently, PELF recovery is overestimated [6,10]. Nevertheless, PELF urea concentration has been shown to be independent of lung disease, which is not the case for albumin, whose diffusion rate is increased by airway inflammation [5].…”