What is the role of pleural fluid glucose and pH levels in the evaluation pleural effusion (fluid on the lungs)?

Updated: Dec 28, 2018
  • Author: Kamran Boka, MD, MS; Chief Editor: Guy W Soo Hoo, MD, MPH  more...
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In addition to the previously discussed tests, glucose and pleural fluid pH should be measured during the initial thoracentesis in most situations.

A low pleural glucose concentration (30-50 mg/dL) suggests malignant effusion, tuberculous pleuritis, esophageal rupture, or lupus pleuritis. A very low pleural glucose concentration (ie, < 30 mg/dL) further restricts diagnostic possibilities, to rheumatoid pleurisy or empyema.

Pleural fluid pH is highly correlated with pleural fluid glucose levels. A pleural fluid pH of less than 7.30 with a normal arterial blood pH level is caused by the same diagnoses as listed above for low pleural fluid glucose. However, for parapneumonic effusions, a low pleural fluid pH level is more predictive of complicated effusions (that require drainage) than is a low pleural fluid glucose level. In such cases, a pleural fluid pH of less than 7.1-7.2 indicates the need for urgent drainage of the effusion, while a pleural fluid pH of more than 7.3 suggests that the effusion may be managed with systemic antibiotics alone.

In malignant effusions, a pleural fluid pH of less than 7.3 has been associated in some reports with more extensive pleural involvement, higher yield on cytology, decreased success of pleurodesis, and shorter survival times.

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