What is the most likely cause of ascites in an adult patient with a history of treated tuberculosis, presenting with progressive abdominal distension, shifting dullness, and ascitic fluid analysis showing a low white blood cell count with a predominance of mesothelial cells, a high serum-ascites albumin gradient (SAAG), and no fever or jaundice?

Most Likely Cause of Ascites: Liver Cirrhosis

Based on the serum-ascites albumin gradient (SAAG) of 2.0 g/dL (35-15 = 20 g/L or 2.0 g/dL), this patient has portal hypertension-related ascites, making liver cirrhosis (Option B) the most likely diagnosis.

Interpretation of the SAAG

The SAAG is the definitive test for categorizing ascites and distinguishing portal hypertension from other causes:

• A SAAG ≥1.1 g/dL (11 g/L) indicates portal hypertension with 97% accuracy 1
• This patient's SAAG is 2.0 g/dL, well above the threshold, confirming portal hypertension as the underlying mechanism 1
• Cirrhosis accounts for 75-85% of all ascites cases and is the most common cause of portal hypertension-related ascites 2

Why Not Tuberculosis?

While the patient has a history of treated tuberculosis, several key features argue strongly against tuberculous peritonitis:

• Tuberculous peritonitis produces a SAAG <1.1 g/dL in patients without coexistent liver disease 1, 3
• The ascitic fluid shows only 80 cells/mm³ with mostly mesothelial cells, whereas tuberculous peritonitis characteristically shows elevated total mononuclear cell counts with lymphocyte predominance 3
• Absence of fever makes active infection unlikely 1, 4
• In tuberculous peritonitis, ascitic fluid protein is typically >25 g/L (2.5 g/dL) in 100% of cases without liver disease and 70% with coexistent liver disease 3, whereas this patient has low ascitic fluid albumin of 15 g/L

Why Not Heart Failure?

Cardiac ascites can also produce a high SAAG (≥1.1 g/dL), but:

• Jugular venous distension is present in cardiac ascites but absent in cirrhotic ascites 1, 2
• The question states no mention of jugular venous distension or cardiac symptoms
• BNP/pro-BNP levels distinguish cardiac from cirrhotic ascites (median pro-BNP 6100 pg/mL in heart failure vs 166 pg/mL in cirrhosis) 2, though not provided here

Why Not Malignancy?

Peritoneal carcinomatosis produces ascites through a different mechanism:

• Malignant ascites produces a SAAG <1.1 g/dL 1
• This patient's SAAG of 2.0 g/dL effectively excludes peritoneal carcinomatosis as the primary cause 1

Clinical Pitfalls to Avoid

Do not be distracted by the tuberculosis history - calcified granulomas represent healed disease and are incidental findings from prior infections 2. The SAAG objectively categorizes the ascites mechanism regardless of past medical history 1.

In patients with coexistent chronic liver disease and tuberculous peritonitis, the SAAG can be elevated (>11 g/L in 52% of cases, or 71% after correction for serum globulin) 3. However, such cases would show:

• Elevated ascitic fluid LDH >90 U/L (present in 84% of TB cases with liver disease) 3
• Elevated mononuclear cell counts 3
• Constitutional symptoms including fever 4, 3

None of these features are present in this case.

Prognostic Implications

Development of ascites in cirrhosis dramatically worsens prognosis, with 5-year survival dropping from 80% in compensated cirrhosis to 30% with ascites development 2. This patient should be evaluated for liver transplantation 2, 5.

Answer: B. Liver cirrhosis