Peripheral blood monocyte level as a biomarker of pulmonary fibrosis severity – an unused opportunity for general clinical laboratory testing?

The development of pulmonary fibrosis (PF) and its progression are the most important determinants of the prognosis of interstitial lung diseases (ILD). Late diagnosis is a global problem that necessitates the search for simple and reliable prognostic biomarkers. The aim of the study was to investigate the potential value of the level of peripheral blood monocytes as a biomarker of ILD severity. Methods. A cross-sectional study was conducted involving patients with ILD ( n = 50). Based on the stratification by the GAP scale (G – gender, A – Age, P – Physiology (lung function parameters)), the patients were divided into 2 groups: group 1 (GAP I) scored from 0 to 3 points on the GAP scale, group 2 (GAP II and III) scored ≥ 4 points. Intergroup comparisons were performed. Subanalyses were conducted to assess the effect of monocytosis on the presence or absence of fibrotic changes according to chest computed tomography (CT) data, as well as to clarify the discriminatory ability of monocytosis as a biomarker of ILD severity and the potential of the cut-off point of the monocyte level of 600 cells/μl. Results. Patients with more severe fibrotic changes according to chest CT data showed a higher serum level of monocytes, and a significant correlation was noted between the degree of monocytosis and the severity of interstitial changes in the lungs according to the Warrick scale. However, a greater degree of decrease in forced vital capacity and forced expiratory volume in 1 second was noted in patients whose monocyte level was equal to or exceeded 600 cells/μl. Conclusion. The study revealed a higher level of monocytes in the peripheral blood of patients with ILD of greater severity according to the GAP scale, and demonstrated the discriminatory potential of the threshold value of the monocyte level equal to and exceeding 600 cells/μl in identifying patients with a higher degree of impairment of the pulmonary ventilation capacity and the prevalence of interstitial changes in the lungs. The ongoing study of non-invasive biomarkers of ILD severity and predictors of LF progression seems to be one of the most pressing issues in modern respiratory medicine.