Answer 1

Low pleural glucose is commonly seen in Rheumatoid Arthritis and it indicates:

1. Thickened pleura, impairing glucose diffusion into pleural space
2. Increased glucose metabolism in pleural space

Answer 2

Patients with complicated parapneumonic effusions tend to have a lower pleural fluid pH and glucose level and a higher LDH activity. The glucose concentration correlates directly with the pH. The cause for pleural fluid acidosis and low glucose levels is the local metabolic activity of inflammatory cells and bacteria.

Soure: http://www.ersj.org.uk/content/10/5/1150.full.pdf