Diagnostic Criteria for Chylous Ascites
The diagnosis of chylous ascites is definitively established by demonstrating an ascitic fluid triglyceride level >200 mg/dL in fluid obtained by paracentesis, which typically appears white and milky on gross examination. 1
Essential Diagnostic Steps
Initial Paracentesis and Fluid Analysis
- Perform diagnostic paracentesis immediately in any patient with suspected chylous ascites to obtain ascitic fluid for analysis 1, 2
- Visual inspection is the first clue: Look for white, milky-appearing peritoneal fluid, which is the hallmark finding that should immediately raise suspicion 1, 3
- Measure ascitic fluid triglyceride level: A concentration >200 mg/dL (>2.26 mmol/L) confirms the diagnosis 1, 3, 4
- In true chylous ascites, triglyceride levels often exceed 1,000 mg/dL 1
Standard Ascitic Fluid Analysis Panel
Beyond triglycerides, obtain the following on the initial paracentesis specimen:
- Cell count with differential to assess for infection or malignancy 1
- Albumin concentration to calculate the serum-ascites albumin gradient (SAAG) 1, 2
- Total protein concentration 1
- Culture if infection is suspected 1
Determining the Underlying Etiology
- Calculate SAAG to distinguish portal hypertension-related causes: SAAG ≥1.1 g/dL indicates portal hypertension with 97% accuracy 5, 1, 2
- This distinction is critical because it determines prognosis and guides treatment strategy 2
- The most common causes in adults are malignancy, cirrhosis, and trauma after abdominal surgery 3, 6
Critical Diagnostic Pitfall
Do not rely solely on visual appearance: Turbid or milky fluid can also result from infection (high neutrophil count) or tumor cells, so triglyceride measurement is absolutely essential for definitive diagnosis 1. The older diagnostic threshold of >110 mg/dL mentioned in some literature 5, 4 is less specific; the >200 mg/dL cutoff provides greater diagnostic certainty 1, 3.
Additional Diagnostic Considerations
- Neutrophil count should be obtained to rule out spontaneous bacterial peritonitis, particularly in cirrhotic patients 5
- Other specialized tests (amylase, cytology, PCR for mycobacteria) should only be performed when the diagnosis is unclear or there is clinical suspicion of pancreatic disease, malignancy, or tuberculosis 5