Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (594 page)

It is clinically important to classify pleural and ascitic fluids into exudates and transudates because this is indicative of the underlying pathophysiologic process involved (Figure
13-1
). A transudate does not usually require additional testing, but exudates always do.

Figure 13–1
Algorithm for the workup of patients with pleural effusion. LDH = lactate dehydrogenase.

Transudate

   Causes

   CHF (causes 15% of cases); acute diuresis can result in pseudoexudate

   Cirrhosis with ascites (pleural effusion in approximately 5% of cases)— rare without ascites

   Nephrotic syndrome

   Early (acute) atelectasis

   PE

   Superior vena cava obstruction

   Hypoalbuminemia

   Peritoneal dialysis—occurs within 48 hours of initiating dialysis

   Early mediastinal malignancy

   Misplaced subclavian catheter

   Myxedema (rare cause)