Variation in the measurements of basement membrane thickness and inflammatory cell number in bronchial biopsies.

We do not have an estimate of how much tissue is needed for a reliable measure of bronchial epithelial reticular basement membrane (RBM) thickness or for counts of inflammatory cells. An assessment of the frequency distribution and variance of data from repeat measurements of RBM thickness and biopsy section inflammatory cell counts in cases with asthma (n=6), chronic obstructive pulmonary disease (COPD; n=5), and normal healthy subjects (n=7) was made. Tissue sections were stained with haematoxylin and eosin or by immunohistochemistry for EG2, mast cell tryptase and CD3-positive cells. Measurements of RBM thickness in individuals followed a log-normal distribution. For a precision of approximately +/-15%, 31-45 measurements were required. In contrast, inflammatory cell counts for each individual did not follow a normal distribution. There was high variance such that the cumulative weighted mean did not become stable until at least 5-10 mm of tissue underlying the RBM had been included. In conclusion multiple measurements of reticular basement membrane thickness or tissue section cell counts should be made for each individual in studies of bronchial biopsies. It is recommended that reticular basement membrane thickness should be measured at 20 mm intervals over a 1 mm reticular basement membrane length and that a zone beneath it of at least 5-10 mm of reticular basement membrane should be included for counts of inflammatory cells.