What laboratory finding indicates rheumatoid arthritis in a pleural effusion?

• A. High pleural glucose
• B. High lymphocytes
• C. Low pleural glucose
• D. Malignant cells

Answer: (C)

In the context of a pleural effusion associated with rheumatoid arthritis, the laboratory finding that is indicative is a low pleural glucose level. This occurs because inflammatory processes, such as those seen in rheumatoid arthritis, can lead to increased consumption or reduced availability of glucose in the pleural space. Inflammatory cells, particularly lymphocytes, may engage in metabolic activities that deplete glucose, resulting in lower levels in the effusion compared to serum glucose levels.

Pleural effusions from rheumatoid arthritis are typically exudative, and they often exhibit elevated levels of certain inflammatory markers, while glucose levels tend to decline. This biochemical environment reflects the active inflammatory state associated with rheumatoid arthritis, as well as the presence of immune-mediated damage. Hence, detecting a low glucose concentration in the pleural fluid can assist in corroborating a diagnosis of rheumatoid arthritis, alongside clinical features and other diagnostic criteria.