Causes of Transudative Pleural Effusion
| Cause | Comment |
|---|---|
| Heart failure | Increased interstitial fluid, which crosses the visceral pleura and enters the pleural space. Investigate further if atypical features are present (unilateral effusion, fever, chest pain). |
| Nephrotic syndrome | Usually bilateral effusions, decreased oncotic pressure causing transudate effusion. |
| Cirrhosis with ascites | Predominantly right-sided pleural effusion and often ascites is present. Ascitic fluid migration to the pleural space through diaphragmatic defects. |
| Hypoalbuminaemia (serum albumin <25g/L) | Associated with oedema. |
| Hypothyroidism | May be transudate or exudate, commonly in combination with ascites, pericardial effusion and cardiac failure. |
| Meigs' syndrome | In women with ovarian or other pelvic tumours (either bilateral or unilateral). |
| Urinothorax | Due to urine obstruction that causes retroperitoneal urine leak. pH usually low, pleural fluid smells of urine and pleural fluid creatinine > serum creatinine is diagnostic. |
| Constrictive pericarditis | Increases IV hydrostatic pressure, associated with oedema. |