The paper aims to highlight the value of laboratory investigations in various pleurisy by exploring the pleural fluid on the three levels (biochemical, bacteriological and cytological), correlating it with the clinical and imaging aspect to establish the etiology of pleurisy. The researches were performed in the Clinical Laboratory within the Bacău Pneumoftiziology Hospital between March and May 2020. To study the characteristics of pleural fluids, a number of 56 subjects diagnosed with pleurisy of different etiologies were analyzed. Laboratory tests were performed on pleural fluid obtained by pleural puncture. The patients investigated were grouped by sex, according to background and age groups. The investigation of pleural fluids on the three levels (biochemical, cytological and bacteriological), correlated with clinical manifestations and radiological aspects led to the diagnosis of patients with the following types of pleurisy: tuberculous pleurisy, parapneumonic, neoplastic, eosinophils and pleurisy due to other causes. In all types of pleurisy, male patients have the highest number of cases. All neoplastic pleurisy was recorded in age group III.
