What is the most likely cause of ascites in a patient with a history of treated tuberculosis, presenting with progressive abdominal distension, ascites, and characteristic ascitic fluid findings?

Most Likely Cause: Malignancy (Peritoneal Carcinomatosis)

Based on the ascitic fluid findings—particularly the low SAAG of 2.0 g/dL (serum albumin 35 g/L minus ascitic fluid albumin 15 g/L = 20 g/L or 2.0 g/dL), low white cell count with predominantly mesothelial cells, and history of treated tuberculosis—this patient most likely has malignancy-related ascites, specifically peritoneal carcinomatosis.

Key Diagnostic Reasoning

SAAG Interpretation

• The SAAG of 2.0 g/dL is >1.1 g/dL, which indicates portal hypertension with 97% accuracy 1, 2, 3
• This high SAAG points toward cirrhosis, heart failure, or Budd-Chiari syndrome as the underlying cause 1
• A SAAG <1.1 g/dL would suggest non-portal hypertension causes including peritoneal tuberculosis, peritoneal carcinomatosis, or pancreatitis 2, 3

Critical Calculation Error Recognition

Wait—let me recalculate: Serum albumin 35 g/L (3.5 g/dL) minus ascitic fluid albumin 15 g/L (1.5 g/dL) = SAAG of 2.0 g/dL. This is actually a high SAAG, not low.

Revised Answer: Liver Cirrhosis

With a SAAG of 2.0 g/dL (≥1.1 g/dL), this patient has portal hypertension-related ascites, and liver cirrhosis is by far the most common cause, accounting for 75-85% of all ascites cases in Western populations and 60% in Asian populations 1, 2, 3.

Why Cirrhosis is Most Likely

Portal Hypertension Confirmed:

• The SAAG ≥1.1 g/dL indicates portal hypertension with 97% diagnostic accuracy 1, 2
• Cirrhosis is responsible for approximately 75-85% of all ascites cases 1, 2

Clinical Presentation Fits:

• Progressive abdominal distension over weeks is typical for cirrhotic ascites 1
• Absence of fever and jaundice makes acute decompensation or infection less likely 1, 2
• Shifting dullness confirms at least 1500 mL of ascitic fluid 1

Low Ascitic Fluid Cell Count:

• The white cell count of 80 cells/mm³ with mostly mesothelial cells is consistent with uncomplicated cirrhotic ascites 1, 2
• This count is well below the 250 cells/mm³ neutrophil threshold for spontaneous bacterial peritonitis 1, 2

Why NOT the Other Options

Tuberculosis (Option A):

• Tuberculous peritonitis causes a SAAG <1.1 g/dL because it does not involve portal hypertension 2, 3
• The patient completed tuberculosis treatment years ago and has been well since 3
• Calcified hepatic granulomas represent healed granulomatous disease and are typically incidental findings from prior infections 3
• Active tuberculous peritonitis would typically present with fever, which this patient denies 1, 4

Heart Failure (Option C):

• While heart failure causes high SAAG ascites, jugular venous distension would be present in cardiac ascites but absent in cirrhotic ascites 1, 3
• The physical examination finding of shifting dullness without mention of elevated JVP makes heart failure less likely 1
• Brain natriuretic peptide levels can distinguish cardiac from cirrhotic ascites (median pro-BNP 6100 pg/mL in heart failure versus 166 pg/mL in cirrhosis) 1, 3

Malignancy (Option D):

• Peritoneal carcinomatosis typically causes a SAAG <1.1 g/dL 1, 2
• Malignant ascites would show atypical or malignant cells on cytology, not predominantly mesothelial cells 1
• The low white cell count with benign mesothelial cells argues strongly against malignancy 1, 2

Clinical Implications

Prognosis:

• Development of ascites in cirrhosis dramatically worsens prognosis, with 5-year survival dropping from 80% in compensated cirrhosis to 30% with ascites 1, 2, 3
• Approximately 15% of patients with ascites die within 1 year and 44% within 5 years 1

Next Steps:

• This patient should be evaluated for liver transplantation given the poor prognosis associated with ascites development 2, 3
• Initiate treatment with dietary sodium restriction (2000 mg/day) and oral diuretics 1
• Screen for hepatocellular carcinoma, portal vein thrombosis, and hepatic vein thrombosis with imaging 1