Finding the right tests…
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Finding the right tests…
Biochemistry
When fluid builds up in the abdomen and the cause isn't obvious from imaging alone, two possibilities are often hardest to tell apart without extra testing: tuberculous peritonitis and cancer that has spread to the abdominal lining. Adenosine deaminase measured directly in that ascitic fluid, drawn during a paracentesis, is one of the more useful ways to separate the two, because tuberculosis drives ADA activity in fluid far higher than cancer does. A study comparing the two groups directly found average ADA levels of roughly 67 U/L in tuberculous peritonitis against roughly 14 U/L in peritoneal carcinomatosis, a gap wide enough that, at a cutoff of 21 IU/L, the test correctly identified about 92 in every 100 tuberculosis cases.
The report gives ADA activity in the ascitic fluid sample, in units per litre. Different studies have used somewhat different cutoffs, but a figure around 21 IU/L has shown sensitivity near 92 percent and specificity near 85 percent for distinguishing tuberculous peritonitis from peritoneal carcinomatosis specifically, rather than from every possible cause of ascites. The same tap is usually tested for cell counts, protein, and albumin, the last of these used to calculate the serum-ascites albumin gradient, since ADA is read alongside that wider picture rather than on its own.
Ascites, fluid collecting in the abdominal cavity, has a long list of possible causes, from liver disease to heart failure to cancer to tuberculosis. Much of that list is narrowed down first using the serum-ascites albumin gradient, which broadly separates ascites linked to portal hypertension from ascites that isn't. Tuberculous peritonitis and peritoneal carcinomatosis, cancer that has spread across the abdominal lining, both tend to fall on the same non-portal-hypertension side of that gradient, which is exactly where they become hard to separate from each other by imaging or the albumin gradient alone.
Tuberculosis triggers a strong local immune response, so the T cells and macrophages fighting the infection release large amounts of ADA directly into the fluid. Cancer cells generally don't drive the same response, so ADA in cancer-related ascites tends to stay much lower. In one comparative study, tuberculous peritonitis averaged roughly 67 U/L against about 14 U/L in cancer-related ascites, and the gap was consistent enough to give the test strong discriminating power in that specific comparison.
A raised ascitic ADA supports a tuberculosis diagnosis strongly enough to influence treatment decisions in settings where tuberculosis is common, but it's still generally paired with imaging, cell counts, and sometimes a biopsy, particularly when the picture isn't clear-cut or the ADA result sits near the cutoff rather than far above or below it.
Ascitic fluid ADA is measured directly in fluid drawn from the abdomen during a paracentesis, where TB-driven immune activity concentrates. Blood ADA reflects a more diluted, whole-body picture and is considerably less sensitive for this purpose.
At a cutoff around 21 IU/L, a high result leans strongly toward tuberculous peritonitis rather than cancer-related ascites, based on research comparing the two conditions directly.
It's one of the stronger tools available for that specific comparison, but it's still read alongside imaging, cell counts, and sometimes a biopsy rather than used as a stand-alone answer.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
It's collected during a paracentesis, a procedure where a doctor draws fluid from the abdominal cavity using a needle, usually with local anaesthesia.
The albumin gradient narrows down the broad cause of ascites first; ADA is then used to separate tuberculosis from cancer specifically, since both can fall on the same side of that gradient.
It leans away from tuberculous peritonitis, but your doctor will weigh it alongside imaging and other fluid findings before ruling anything out.