Sputum is usually a combination of saliva and mucus that forms in a person's lungs. To collect a sputum sample, doctors generally have the patient cough deeply and spit into a cup. There are often some precautions taken to avoid any contamination of the sample, and sometimes the patient has to drink extra fluid to increase the quantity of the lung secretion. In other situations, doctors have to suck out the sputum through a tube inserted into the nose that runs back to the throat. This method is especially common for patients who are too severely ill to cough up their own samples—sometimes, doctors may even have to take those samples with a syringe inserted through the throat.
When taking a sputum sample, doctors sometimes ask the patient to cleanse her mouth first. This is often done very carefully to avoid adding any chemicals to the sample. Chemicals can sometimes kill bacteria or viruses, and the whole purpose of collecting sputum samples is usually to see if there is anything foreign living inside someone’s lungs. The safest way to cleanse the mouth is typically to rinse with water.
After they collect the sputum, doctors will generally use portions of the samples to test for various infections. This is done by putting sputum on foods that different kinds of bacteria and other foreign invaders like to eat. If anything grows on these foods, it tells the doctors what kind of infection the patient is suffering from. This can be useful for doctors when determining best treatment approaches for someone with a respiratory illness. It’s sometimes especially necessary when the illness is mysterious and isn’t responding to normal treatment measures.
Sometimes patients can have a hard time coughing up a good sputum sample. In those situations, doctors may ask the patients to drink some water and then come back in an hour or so for another attempt. Dehydration is one of the most common problems when collecting sputum because it lessens the available fluid in the lungs. Drinking water is generally the most obvious way to deal with this problem, but there are also others.
Doctors will sometimes insert a tube into the breathing passage to directly add fluid to the lungs. This fluid generally mixes with dried up mucus, and when the patient coughs it up, it’s basically equivalent to a normal sputum sample. This procedure can sometimes be somewhat uncomfortable, so doctors will usually sedate patients first.