For those of us working in medical laboratories, stool samples for TB diagnosis are not common, and faeces may not seem connected to Tuberculosis at first glance. They’re often dismissed as ‘dirty, smelling samples’ that we, as medical scientists, may not appreciate, but we have no choice. As a medical laboratory scientist, I’ve seen it all. Even the patients who produce these samples would rather not spend time with them. It’s a unique part of our job.
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Stool Samples And Mycobacterium Tuberculosis(TB)?
First, Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis. It primarily affects the lungs. Those with active TB infection usually have a persistent cough, chest pain, night sweats, weight loss and many other symptoms.
This is why sputum samples are primarily associated with a possible Tuberculosis infection in the lab and are usually processed in a biosafety cabinet.
However, this is not the case with stool samples. Unfortunately, Mycobacterium Tuberculosis can be found in stool samples of patients with active TB infections. For this reason, laboratory staff are advised to handle any patient samples as potentially infectious.
Patients suspected of having TB are usually asked to provide sputum. They do this by coughing out sputum(not saliva) into a clean container provided by the lab where the test would be done. As far as TB testing is concerned, Sputum samples are the gold standard.
However, some patients find it difficult to cough or produce sputum. In this case, stool or faeces can be used as an alternative to sputum. Before stool, there are alternatives like gastric washings and bronchoalveolar lavage(BAL), but the process is painful or invasive to some degree.
There are class of patients where Doctors can consider the use of stool for suspected TB diagnosis which I will discuss below.
TB Diagnosis in Children, HIV and Other Immunocompromised Patients.
Some children can’t really produce good quality sputum when asked to. Some will end up producing saliva which is not sputum. Some HIV and immunocompromised patients may be too weak to even cough , let alone producing quality sputum.
Children, can cough and swallow their phlegm(sputa). This is how the Mycobacteria tuberculosis find its way from the lungs into the gut and mix with the stool or faeces and finally passes with the stool when the patients uses the toilet.
Why stool sample?
Stool samples offer some advantages over other conventional methods. They are non-invasive, easy to collect. Children and people living with HIV (PLHIV) who often struggle to produce adequate sputum samples can easily pass stool that can be used TB test.
The other side of the story is that you will need to standardize the process of testing TB with stool. This is challenging but its a excellent alternative when sputum production is difficult in certain patient category. In your facility, you could treat stool sample the way you treat sputa when processing it in using molecular technique like The GeneXpert machine by cepheid.
