When and why

If active tuberculosis is suspected, on account of a persistent cough, then it is important to find out if tuberculosis mycobacteria are, in fact present. The simplest way to do this is to collect a sample of the fluid that is being coughed up - the sputum or phlegm. Once collected, this is stained to examine under a microscope and an attempt can be made to culture the organisms.

This procedure is most likely to succeed if the sample is taken first thing in the morning, when the lungs are being cleared of fluid that has built up during sleep (when coughing is suppressed).

If it is still hard to collect a sample, a doctor or nurse may ask you to inhale a fine mist of salty water, which is a harmless procedure that is usually very effective in bringing up a test sample.

It is important that this procedure is not carried out on an open ward or indeed any shared space where people who may be vulnerable to TB are exposed to whatever may be coughed up.

How it will help

If TB is present, it can and must be treated. If TB is present in sputum, a person is considered infectious to others and may need to have a separate room, possibly with special ventilation, until treatment has made that person non-infectious.

Culture of TB organisms is necessary in order to assess drug resistance and ensure that treatment given is truly effective.