REPEATABILITY OF MEASURES OF INFLAMMATORY CELL NUMBER IN BRONCHIAL BIOPSIES IN ATOPIC ASTHMA

Airway pathology is increasingly considered to be a major outcome in a sthma research. The aim of this study was to examine the intra-observe r, within-section and between-biopsy repeatability, together with the implications for statistical power of a computerized quantitative anal ysis of inflammatory cell numbers in the lamina propria in bronchial b iopsy specimens from atopic asthmatic subjects. Thirty six atopic adul ts (aged 19-40 yrs) with mild to moderate asthma (baseline forced expi ratory volume in one second (FEV1) greater than or equal to 50% of pre dicted value, methacholine (PC20) range 0.02+/-18.2 mg.mL(-1)) at vari ous levels of treatment (25 subjects on inhaled steroids) entered the study. Biopsies were taken from the (sub)segmental carinae of the righ t lower and middle lobe and from the main carina. Specimens were snap- frozen and immunohistochemical staining was performed on cryostat sect ions with monoclonal antibodies against: (secreted) eosinophil cationi c protein (EG1, EG2), mast cell tryptase (AA1), CD45, CD22, CD4, CDS, CD25, and CD45RO. Using a computerized system, the number of positivel y stained cells in the lamina propria was counted. When considering al l cell types together, satisfactory intraclass correlation coefficient s (ICC) values were obtained for intra-observer, within-section and be tween-biopsy repeatability, being 0.90, 0.80 and 0.81, respectively. T he analysis of repeatability for individual cell types revealed ICC va lues ranging 0.47-0.82 for intra-observer, 0.44-0.76 for within-sectio n and 0.37-0.67 for between-biopsy repeatability. The results imply th at a sample-size between eight and 25 subjects is needed to detect at least one doubling difference in cell number per 0.1 mm(2) for a parti cular inflammatory cell type in a study, using a within-group design w ith alpha=0.05 and power of 0.80. A sample-size of 13-48 subjects per group is required to detect the same difference between the groups in a parallel design.