Useful basic clinical tests
| Clinical test | Rationale |
|---|---|
| Routine tests | |
| Complete blood cell count | Abnormal blood cell counts can suggest infection or cancer* |
| Serum LDH, protein | To apply Light’s criteria |
| Pleural LDH, protein | To apply Light’s criteria |
| Pleural pH, glucose | To identify complicated parapneumonic effusions |
| Pleural fluid culture | To identify infectious agents |
| Pleural fluid cytology | To diagnose malignant disease |
| Contrast chest CT for exudates | To identify mediastinal/pleural/lung lesions |
Note: CT = computed tomography, LDH = lactate dehydrogenase. Light’s criteria: An effusion with any of the following characteristics is classified as an exudate: pleural:serum ratio > 0.5, pleural:serum LDH ratio > 0.6 or pleural LDH > 2/3 of the upper limit of normal for the serum. An effusion with none of these characteristics is classified as a transudate. (6)
↵* For a more detailed discussion on the value of cellular counts and differentials, readers should consult the guideline published by the British Thoracic Society. (1)