How can I differentiate between transudative and exudative ascites based on laboratory findings?

To differentiate between transudative and exudative ascites based on laboratory findings, the Serum-Ascites Albumin Gradient (SAAG) is the most accurate and widely used parameter NICE CKSHuang et al. 2014. The SAAG is calculated by subtracting the ascitic fluid albumin concentration from the serum albumin concentration NICE CKSHuang et al. 2014.

Transudative ascites is indicated by a SAAG of 1.1 g/dL or greater (≥ 1.1 g/dL) NICE CKSHuang et al. 2014. This type of ascites is typically caused by portal hypertension, commonly seen in conditions such as cirrhosis or heart failure NICE CKSHuang et al. 2014.

Exudative ascites is indicated by a SAAG of less than 1.1 g/dL (< 1.1 g/dL) NICE CKSHuang et al. 2014. Exudative ascites is generally associated with inflammation, infection, or malignancy NICE CKSHuang et al. 2014.

While SAAG is the primary differentiator, other ascitic fluid parameters can provide further diagnostic clues, particularly for exudative causes NICE CKSHuang et al. 2014. These include total protein, lactate dehydrogenase (LDH), glucose, and cell count with differential NICE CKSHuang et al. 2014. For instance, a high ascitic fluid total protein concentration (typically > 2.5 g/dL) was historically used to classify exudates, but SAAG is now considered superior NICE CKSHuang et al. 2014.