A pleural fluid specimen was collected into an anticoagulant‐free tube at the time of patient admission. After centrifugation, the supernatant of the pleural fluid was collected and stored at −70°C until analysis. In both cohorts, homocysteine was measured by a Beckman AU5800 biochemical analyzer in November 2021. The coefficient variations (CVs) of homocysteine were 2.83% and 8.92% at concentrations of 23.35 and 5.53 μmol/L, respectively. The laboratory technician who measured the homocysteine level did not know the patients' clinical details.
Pleural fluid concentrations of glucose, adenosine deaminase (ADA), white blood cells (WBCs), lactate dehydrogenase (LDH), and protein were collected from the medical records of the participants. Pleural glucose was determined by the hexokinase method. LDH was determined by the lactate‐to‐pyruvate method. ADA was determined by the peroxidase method.21 Total protein was determined by the biuret method. LDH, ADA, and glucose were determined by a Beckman AU5800 biochemical analyzer. WBC counts in the pleural fluid were determined by a Sysmex XN 2000 hematology analyzer.
Pleural fluid concentrations of glucose, adenosine deaminase (ADA), white blood cells (WBCs), lactate dehydrogenase (LDH), and protein were collected from the medical records of the participants. Pleural glucose was determined by the hexokinase method. LDH was determined by the lactate‐to‐pyruvate method. ADA was determined by the peroxidase method.