Intrasubject variability in airway inflammation in biopsies in mild to moderate stable asthma.

Abstract

We have studied intrasubject variability with respect to counts of immunostained inflammatory cells in snap frozen endobronchial biopsies from a group of patients with clinically mild to moderate stable asthma. Fiberoptic bronchoscopy was used to obtain endobronchial biopsies from the upper and lower lobes in 12 volunteer subjects with asthma on two separate occasions 1 mo apart. During this period there was no significant change in asthma treatment, symptom scores, pulmonary function, or airway hyperresponsiveness. With the aid of immunohistochemistry and interactive image analysis, subepithelial counts for T lymphocytes, T-lymphocyte subsets, and eosinophils were made. There was wide intrasubject variability between anatomic site and with time for all the inflammatory cell counts. In each case the intrasubject variability with time was greater than lobar differences. Power calculations were made to establish the optimal sample size required for each marker. We conclude that even in stable asthma considerable biologic variability compounds sampling variability. Such sources of variability need to be borne in mind when calculating the likely power of intervention studies using biopsy data as end points. Power calculations suggest that approximately 15 subjects would be an optimal number with little advantage in increasing beyond this.

Repeatability of measures of inflammatory cell number in bronchial biopsies in atopic asthma

“…Indeed, we found that the difference between two counts was positively related to their mean for all of the inflammatory cell types. Furthermore, when looking carefully at the data of RICHMOND et al [8], the variability also increased with increasing mean cell counts. This implies that there was heteroscedasticity, in other words, that the variability increased with increasing severity of the inflammatory cell infiltrate, which is to be avoided for statistical analysis [9].…”

“…Very recently, a study by RICHMOND et al [8], aimed at the quantification of variability, showed that there is indeed considerable within-subject variation of inflammatory cell counts between biopsy sites and with time in patients with asthma. Reanalysing their between-site data revealed ICC values of 0.80 when considering all cell types together, and 0.25-0.80 for the individual cell types, thereby demonstrating similar repeatability as in the present study.…”

“…There is only sparse information on the variability of inflammatory cell numbers between biopsies of different sites and within-sections [8]. Such data would have implications for the statistical power of intervention studies with outcome measures obtained from biopsy specimens.…”

Bronchial biopsies and airway inflammation

“…Biopsies sample only a fragment of the surface of a very large bronchial tree and it has been reassuring to note that the largest contribution to variation is between subjects rather than between distinct generations of airway [55,68,69]. It is estimated that 15 subjects per group should provide sufficient statistical power to detect most of the changes of interest in biopsies of inflamed airways [70]. Most biopsy studies reported in the literature, understandably, have not managed to obtain this number, which means that essential information is being lost to interpretation.…”

Variability of markers of airway inflammation in BAL

“…In summary, we would like to point out that the purpose of our study, together with a recently published paper relating to biopsy work [5], was not to didactically construct absolute numbers for study design, but was rather an attempt to contribute to a development of methodology in an increasingly important area of clinical research. We would like to thank Dr Pizzichini and colleagues for their interest and constructive questioning, and the European Respiratory Journal for publishing our work.…”