Interpretation of bronchoalveolar lavage fluid cytology - ILD care

Table 1. - Characteristics of the study subjects.
Groups n m* Age Female Male NSm Sm
Interpretation of BALF cytology
Controls 30 0 33 (21-55) 15 15 15 15 (14.9±8.8)
Learning set
Sar 193 3 35 (18-79) 96 94 145 45 (15.7±7.8)
EAA 39 1 50 (23-78) 14 24 34 4 (12.8±6.9)
IPF 45 1 60 (30-79) 16 28 27 17 (18.0±5.1)
Test set
Sar 91 0 37 (17-77) 55 36 79 12 (15.7±6.1)
EAA 5 0 52 (40-66) 1 4 3 2 (20.0±5.0)
IPF 32 0 66 (50-79) 6 26 21 11 (17.4±8.1)
Definition of abbreviations: m=missings, *missing at least one discriminating variable and thus not used in analysis;
Mean with range in parentheses; NSm=Nonsmokers; Sm=Smokers; Number of smokers, mean number of cigarettes a
day ± standard deviation in parentheses; Sar=sarcoidosis; EAA=extrinsic allergic alveolitis; IPF=idiopathic pulmonary fibrosis.
In order to test the predictive power of the computer program based on the logistic model fitted in the learning set
described previously, we used a set of 128 patients from another hospital (i.e., the Rijnstate Hospital, Arnhem, the
Netherlands) who had sarcoidosis, EAA, or IPF. The diagnostic procedures used for this test population were
comparable with those for the population that we used to develop the computer program (the learning set). In
summary, the diagnoses of sarcoidosis and IPF were proven histologically by biopsy, and the diagnosis of EAA was
confirmed by clinical information, chest radiography, pulmonary function testing, the presence of precipitins in
peripheral blood, and the disappearance of the symptoms after avoidance of the causative antigen, or, in some
cases, after a short course of treatment with corticosteroids. Table 1 lists the characteristics of the control subjects
and patient groups studies. The study was approved by the ethical committees of both participating hospitals.
Bronchoalveolar lavage
As reported previously [1], BAL was performed during fiberoptic bronchoscopy. Because the BAL procedure was
the same in both hospitals, the results were fully comparable. The patients were premedicated with atropine and
sometimes diazepam or codeine, and given local anaesthesia of the larynx and bronchial tree (tetracaine 0.5%).
BAL was performed by standardized washing of the middle lobe with four 50-mL aliquots of sterile saline (0.9%
NaCl) at 37 o C. Peripheral blood samples were taken simultaneously.
Recovered BALF was kept on ice in a siliconized specimen trap, and was separated from cellular components by
centrifugation (5 min, at 350 x g). Supernatants were directly stored at -70 o C after an additional centrifugation step
(10 min, at 1,000 x g). Cells were washed twice, counted, and suspended in minimal essential medium (MEM; Gibco,
Grand Island, NY) supplemented with 1% bovine serum albumin (BSA; Organon Teknika, Boxtel, the Netherlands).
Preparations of cell suspensions were made in a cytocentrifuge (Shandon, Runcorn, UK). Cytospin slides of
BALF cells were stained with May-Grünwald-Giemsa (MGG; Merck, Darmstadt, Germany) for cell differentiation. At
least, 1,000 cells were counted.
Statistical methods
In order to distinguish the three diagnostic groups from one another, a polychotomous logistic regression analysis
[17,18] was done on the learning set, according to the following procedure: Each of the 277 patients in the learning
set belonged to one and only one diagnostic group. Five of the cases (three sarcoidosis patients, one EAA patient,
and one IPF patient) had at least one missing discriminating variable, and 272 cases were therefore used for the
analysis. Of these, 190 patients belonged to the sarcoidosis group, 38 to the EAA group, and 44 to the IPF group
(Table 1). Hence, an arbitrary patient within the total learning set had a probability of 190/272=0.70, 38/272=0.14
Software to evaluate BALF analysis. Drent et al. Am J Respir Crit Care Med 1996.
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