Ascitic Fluid Analysis for Abdominal Tuberculosis
In suspected abdominal TB with ascites, perform diagnostic paracentesis and measure adenosine deaminase (ADA) levels in the ascitic fluid, as ADA >27 U/L has 100% sensitivity and 97% specificity for tuberculous peritonitis. 1, 2
Initial Diagnostic Approach
Perform immediate diagnostic paracentesis on all patients with new-onset ascites or suspected abdominal TB, as this is the most rapid and cost-effective diagnostic method. 3 The procedure is safe even with coagulopathy (complications occur in only 1% of cases, primarily minor abdominal wall hematomas). 3
Essential Ascitic Fluid Tests for TB Evaluation
Order the following tests on the initial paracentesis specimen:
Cell count with differential: Look for lymphocyte predominance (typically >50% lymphocytes) with elevated total mononuclear cells, which strongly suggests TB peritonitis rather than bacterial infection. 1, 4 A polymorphonuclear neutrophil (PMN) count <250 cells/mm³ effectively rules out spontaneous bacterial peritonitis. 3, 1
Adenosine deaminase (ADA) level: This is the single most important test for diagnosing tuberculous peritonitis. 3, 1 ADA >27 U/L in cirrhotic patients has meta-analysis-proven sensitivity of 100% and specificity of 97%. 1, 2 This test should be ordered routinely when TB is suspected. 3
Total protein and LDH: Elevated levels (protein >25 g/L, LDH >90 U/L) favor tuberculosis over other causes. 1
Serum-ascites albumin gradient (SAAG): Calculate this to determine if portal hypertension is contributing. SAAG ≤1.1 g/dL suggests peritoneal carcinomatosis or tuberculosis rather than portal hypertension alone. 1
Mycobacterial culture: Inoculate at least 10 mL of ascitic fluid into blood culture bottles at bedside before any antibiotics. 3 However, recognize that culture sensitivity is only approximately 50% for tuberculous ascites. 3, 5
Critical Diagnostic Pitfalls
Do not use the PMN count threshold of ≥250 cells/mm³ to evaluate for TB peritonitis—this threshold is specifically for bacterial spontaneous bacterial peritonitis and does not apply to TB, which presents with lymphocyte predominance rather than neutrophil predominance. 1
Avoid relying on acid-fast bacilli (AFB) smear microscopy, as sensitivity is approximately 0% in ascitic fluid. 3 Even Xpert MTB/RIF assay on ascitic fluid has only 70.6% sensitivity compared to culture. 5
Do not assume negative TB skin testing rules out abdominal TB—only 27% of patients with confirmed abdominal TB have positive TB skin tests. 6
When Initial Testing is Inconclusive
If ADA is elevated (>27 U/L) but cultures remain negative and clinical suspicion persists:
Proceed to laparoscopy with peritoneal biopsy, which is the most rapid and accurate method for diagnosing tuberculous peritonitis. 3, 4 Peritoneal biopsy shows granulomas in 97% of cases and is positive for smear/culture in 68%. 6
Imaging Findings Supporting TB Diagnosis
CT scan abnormalities occur in 80% of abdominal TB cases and may show: 6
- Ascites with variable density (20-45 Hounsfield units depending on disease stage) 3
- Peritoneal thickening 4
- Multiple mesenteric lymph nodes with peripheral enhancement and central hypodensity 3
- Lipohydric level in association with necrotic lymph nodes (highly specific for tuberculous ascites) 3
Clinical Context Considerations
High-risk populations include patients with recent immigration from TB-endemic areas, HIV/AIDS, or other immunocompromised states. 3 In immunocompromised patients from high-prevalence regions, maintain a very low threshold for TB testing even with atypical presentations. 3
Classic presentation includes fever (70-75%), abdominal pain (65-70%), weight loss (68%), and ascites (61-67%). 3, 6 However, up to 85% of patients with abdominal TB have no pulmonary involvement. 3
Treatment is primarily medical with standard anti-TB therapy for 9-12 months, with excellent prognosis (91% recovery rate) if promptly diagnosed and treated. 6 Surgical intervention is reserved only for complications such as perforation. 3