Finding the right tests…
Emergency services available 24 x 7
Emergency services available 24 x 7
Finding the right tests…
Biochemistry
Adenosine deaminase measured in fluid from around the lung is one of the faster tools for judging whether tuberculosis is causing a pleural effusion, since a fluid culture for TB can take weeks and still misses many true cases. ADA rises because it's concentrated in the white blood cells that cluster at sites of tuberculous inflammation, so a high level reflects that immune response directly. A cutoff of 40 IU/L catches essentially all tuberculous effusions but also flags many non-tuberculous ones, particularly where malignancy is common — one study found over half of patients with ADA in the 40 to 70 IU/L gray zone had a malignant effusion, not TB. Some settings now use a higher cutoff, around 70 IU/L.
This test measures the activity of adenosine deaminase, an enzyme, in fluid drawn from the pleural space around the lung. ADA is concentrated in lymphocytes, the white blood cells that build up at sites of tuberculous inflammation, so a raised level in pleural fluid points toward that kind of immune activity. The result is compared against a cutoff value, though which cutoff is used can differ depending on how common tuberculosis is in the local population being tested.
One study comparing cutoffs found that 40 IU/L gave 100% sensitivity but only 61% specificity for tuberculous pleural effusion — it rarely misses a true TB case but also flags a lot of non-tuberculous fluid as suspicious. Raising the cutoff to 70 IU/L brought sensitivity down to 93% while specificity rose to the same level, trading a small chance of missing a case for far fewer false alarms.
In that study, patients whose ADA fell in the 40 to 70 IU/L range mostly did not have tuberculosis — only about 6% did, while more than half had a malignant effusion instead. As TB becomes less common and cancer more so, a fixed low cutoff increasingly points toward the wrong diagnosis, which is part of why some centres use the higher threshold.
Some research has combined ADA with the fluid's LDH level, using a ratio of the two. One study of 382 patients found this combined ratio distinguished tuberculous from non-tuberculous effusions with sensitivity and specificity around 94 to 95%, notably better than ADA alone.
Pleural fluid culture for TB remains the more definitive test, but its sensitivity is only around 30%, and results take time. ADA doesn't replace culture — it gives a faster signal that helps decide on treatment while culture is still pending.
It raises the likelihood that tuberculosis is causing the fluid buildup around the lung, since ADA reflects the type of immune response seen in tuberculous inflammation. It supports a diagnosis rather than confirming one on its own.
One study found a lower cutoff of 40 IU/L rarely misses tuberculosis but often flags non-tuberculous causes too, while a higher cutoff of around 70 IU/L trades a small drop in sensitivity for far better accuracy. Which cutoff is used can depend on how common TB is locally.
Yes, particularly at moderate levels. One study found that of patients with ADA between 40 and 70 IU/L, over half actually had a malignant pleural effusion rather than tuberculosis, which is why the result is always read alongside other findings.
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.
Pleural fluid culture for TB can take weeks and only detects the bacteria in around 30% of true cases. ADA gives a much faster result, which is useful for deciding on treatment while culture is still pending.
Yes. Some research has combined pleural fluid ADA with LDH into a single ratio, which one study found improved both sensitivity and specificity to around 94 to 95%, better than ADA measured alone.
Pleural fluid LDH and protein, used for Light's criteria, along with cell counts and cytology, are commonly checked on the same sample to build a fuller picture alongside ADA.