Normal Protein Level in Ascitic Fluid
In cirrhotic ascites, the normal total protein level is typically <1 g/dL, though it can range up to 2.5 g/dL, whereas in tuberculous peritonitis, protein levels are characteristically elevated to ≥2.5 g/dL or higher. 1
Protein Levels by Etiology
Cirrhotic Ascites (Portal Hypertension)
- Total protein is typically <1 g/dL in uncomplicated cirrhotic ascites, though values up to 2.5 g/dL can occur 1
- A total protein concentration <1.5 g/dL is considered a risk factor for spontaneous bacterial peritonitis (SBP) 2
- The combination of high SAAG (≥1.1 g/dL) with low protein (<2.5 g/dL) is the classic pattern for cirrhotic ascites 1
Tuberculous Peritonitis
- Protein content of ≥2.5 g/dL or more is diagnostic when combined with predominantly lymphocytic count >100/mm³ 3
- In one study, protein levels >3.0 g/dL with >50% lymphocytes were used as diagnostic criteria for tuberculous peritonitis 4
- The elevated protein distinguishes tuberculous ascites from cirrhotic ascites, making this a critical differentiating feature 3, 4
Critical Clinical Context
When Evaluating Suspected Abdominal Tuberculosis
The protein level must be interpreted alongside other parameters:
- SAAG calculation: A SAAG <1.1 g/dL excludes portal hypertension and suggests tuberculous peritonitis or peritoneal carcinomatosis 2, 1
- Cell count: Lymphocytic predominance (>50% lymphocytes) with total count >100/mm³ strongly supports tuberculosis 3, 4
- ADA levels: Use ≥32-40 U/L threshold in non-cirrhotic patients or ≥27-32 U/L in cirrhotic patients for diagnosis 5
Important Pitfall to Avoid
Tuberculous peritonitis occurring in a patient with concurrent cirrhosis can yield falsely low protein levels, which confounds diagnosis and reduces the sensitivity of other diagnostic tests 1. In this scenario, do not rely on protein alone—prioritize ADA testing and consider laparoscopic biopsy if ADA is equivocal 5.
Diagnostic Algorithm for Protein Interpretation
Measure total protein, albumin (for SAAG), and cell count with differential simultaneously 2, 1
If protein <1.5 g/dL with high SAAG (≥1.1 g/dL): Think cirrhotic ascites; assess for SBP risk and consider primary prophylaxis 2
If protein ≥2.5 g/dL with low SAAG (<1.1 g/dL) and lymphocytic predominance: Strongly suspect tuberculous peritonitis; proceed immediately to ADA testing 5, 3
If protein ≥2.5 g/dL with high SAAG (≥1.1 g/dL): Consider cardiac ascites rather than cirrhotic or tuberculous etiology 2, 1
If protein ≥1 g/dL combined with glucose <50 mg/dL and elevated LDH: This combination has 100% sensitivity for secondary bacterial peritonitis from gut perforation—obtain urgent surgical consultation 1