From the Guidelines
Ascitic fluid can be used to diagnose tuberculosis (TB), but its sensitivity is limited, and it should be used in combination with other tests, such as adenosine deaminase (ADA) assay, acid-fast bacilli (AFB) smear, and culture, as well as clinical evaluation and risk factors. When diagnosing TB using ascitic fluid, it is essential to consider the patient's overall clinical picture, including symptoms, risk factors, and other TB manifestations. The ADA assay has been shown to be useful in diagnosing tuberculous peritonitis, with a sensitivity of 100% and a specificity of 96.6-100% when the ADA value is higher than 32-40 U/L in patients without cirrhosis 1. However, in patients with liver cirrhosis, the ADA assay may have lower sensitivity, and a cut-off value of 27 U/L has been suggested to improve diagnosis 1. Other tests, such as PCR testing for mycobacteria or laparoscopy with biopsy and mycobacterial culture of tubercles, may provide more rapid and accurate diagnosis of tuberculous peritonitis 1. Key points to consider when using ascitic fluid to diagnose TB include:
- The ADA assay can be useful in diagnosing tuberculous peritonitis, but its sensitivity may be lower in patients with liver cirrhosis
- A combination of tests, including ADA assay, AFB smear, and culture, as well as clinical evaluation and risk factors, is often necessary for definitive diagnosis
- PCR testing and laparoscopy with biopsy may provide more rapid and accurate diagnosis
- The overall clinical picture, including symptoms, risk factors, and other TB manifestations, should be considered when diagnosing TB using ascitic fluid 1.
From the Research
Ascitic Fluid Analysis for TB Diagnosis
- Ascitic fluid analysis can be used to diagnose tuberculosis (TB) in patients with ascites, but its accuracy and sensitivity vary depending on the method used 2, 3, 4, 5.
- The analysis of ascitic fluid can include parameters such as total protein concentration, cell count and differential, adenosine deaminase (ADA) activity, and culture for Mycobacterium tuberculosis 6, 4, 5.
Diagnostic Parameters
- Elevated ascitic fluid total protein concentration (> 25 g/L) and ADA activity can be indicative of tuberculous peritonitis, but their sensitivity and specificity can be affected by the presence of chronic liver disease 4, 5.
- The serum-ascites albumin gradient (SAAG) can be useful in differentiating between portal hypertensive and non-portal hypertensive causes of ascites, but its value can be limited in patients with coexistent chronic liver disease 4.
- Ascitic fluid lactate dehydrogenase (LDH) level (> 90 U/L) can be a useful parameter for screening for tuberculous peritonitis, especially in patients with suspected TB and coexistent chronic liver disease 4.
Diagnostic Methods
- Xpert MTB/RIF assay can be used to detect Mycobacterium tuberculosis in ascitic fluid samples, but its sensitivity and specificity can vary depending on the study population and the presence of chronic liver disease 3.
- Culture for Mycobacterium tuberculosis is considered the gold standard for diagnosing TB, but it can take several weeks to obtain results 2, 3, 4.
- Laparoscopy with peritoneal biopsy and culture can be a useful diagnostic tool for confirming tuberculous peritonitis, especially in patients with suspected TB and coexistent chronic liver disease 2, 4.
Limitations and Challenges
- The diagnosis of tuberculous peritonitis can be challenging, especially in patients with coexistent chronic liver disease, due to the non-specific nature of the clinical and laboratory findings 2, 4, 5.
- The sensitivity and specificity of ascitic fluid analysis and diagnostic methods can vary depending on the study population and the prevalence of TB in the region 3, 5.