The aim of this study was to investigate the predictive value of peripheral eosinophil and monocyte blood counts regarding lung function in smokers and non-smokers, and to investigate the influence of smoking on these cell counts.
Forced expiratory volume in 1 s (FEV1) measurements and blood samples were collected from 298 non-atopic smokers and 136 never-smokers. Blood samples were repeated in 160 smokers after cessation of smoking (quitters) and 30 continuing smokers, 2, 6, 12 and 26 weeks after smoking cessation.
Monocyte (P<0·05) but not eosinophil blood counts were higher in never-smokers compared to smokers. In never-smokers, blood eosinophil counts and monocyte counts correlated inversely (P<0·05) and directly (P<0·01), respectively, with standardized FEV1 residuals (FEVR). In smokers, blood eosinophil (P<0·05) and monocyte (P<0·05) counts correlated directly with FEVR independent of smoking history. After smoking cessation, monocyte blood counts (P<0·05) increased. Both eosinophil and monocyte blood counts showed a greater increase in quitters with decreased lung function (P<0·05). Former heavy smokers had higher blood eosinophil (P<0·05) but lower monocyte (P<0·05) count increase than had former light smokers.
These data suggest that smoking influences eosinophil and monocyte blood counts and that this is associated with a small negative effect on lung function. Eosinophil blood counts had an opposite relation to lung function in smokers and non-smokers. Further research should include investigations of relations between smoking and stimulatory factors for recruitment and activity of eosinophils and monocytes.