Finding the right tests…
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Finding the right tests…
Molecular
PCR for tuberculosis on pus is used when a collection of pus, often called a cold abscess, has formed under the skin, along the chest wall, near the spine, or wherever TB has broken down tissue and walled itself into a pocket. Because pus concentrates bacteria far more than fluid drawn from a body cavity, a published series testing this method across specimen types found pus and wound samples returned the highest detection rate of any specimen type tested, ahead of pleural fluid, ascitic fluid, or cerebrospinal fluid tested the same way. The sample is usually collected by needle aspiration or from a draining sinus, without needing surgery.
A positive result confirms TB as the cause of the abscess and lets your doctor start treatment, often alongside drainage of the pus itself. A negative result is less common here than with fluid-based TB tests, since pus concentrates bacteria, but it can still happen if the sample came from a long-standing or partly treated abscess with fewer live organisms left. Your doctor will usually combine this with a direct microscopy check for TB bacteria on the same pus sample, and consider a culture if PCR is negative but suspicion stays high.
TB doesn't always stay in the lungs. It can break down tissue, most often near lymph nodes, the chest wall, the spine, or a joint, and collect into a pocket of pus doctors call a cold abscess - cold because, unlike a typical bacterial abscess, it isn't red, hot, or acutely painful. PCR on the pus from this pocket is one of the more reliable ways to confirm TB as the cause.
Pus concentrates far more bacteria in a small volume than fluid drawn from a body cavity does. In a published comparison of nested PCR across specimen types, pus and wound-associated samples returned the highest positive rate of any category tested, ahead of pleural effusion, ascitic fluid, and cerebrospinal fluid run through the identical method. Direct microscopy also performs better on pus than on fluid, though it still misses cases PCR catches.
Pus is typically drawn out with a needle, called aspiration, or collected from an already-draining sinus tract, without the more invasive procedure a biopsy needs.
Pus sent for TB PCR is tested differently from a standard pus culture done for an ordinary bacterial infection. A routine culture grows fast bacteria within a day or two; M. tuberculosis grows far too slowly for that, so a dedicated TB request, PCR plus microscopy, is made separately.
It's a pocket of pus that forms when TB breaks down tissue, most often near a lymph node, the chest wall, or the spine. It's called 'cold' because, unlike a typical bacterial abscess, it often isn't red, hot, or acutely painful.
Pus concentrates far more bacteria in a small volume than fluid drawn from an open body cavity does. In a published comparison of specimen types, pus and wound samples returned the highest TB detection rate of any category tested, ahead of pleural or ascitic fluid.
It's usually drawn out with a needle, called aspiration, or collected from an already-draining sinus tract, without needing a surgical procedure. Ask your doctor or the centre what to expect for your specific case.
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.
Yes, though it's less common here than with fluid-based TB tests, since pus concentrates bacteria more. A long-standing or partly treated abscess can have fewer live organisms left to detect, so your doctor may still rely on direct microscopy or culture on the same sample.
Often, yes. Draining a TB abscess is frequently part of managing it, and the pus removed during drainage can double as the sample sent for PCR and microscopy.
A routine pus culture grows fast, ordinary bacteria within a day or two, but M. tuberculosis grows far too slowly for that method to catch it. TB testing on pus needs a dedicated request, PCR plus direct microscopy, done separately from a standard culture and sensitivity test.