Different bacteria have different ways of responding to staining agents, and this allows scientists to differentiate between them. Usually bacteria are identified by adding colouring agents to the laboratory surface on which they grow. In both tests, the aim is to find Mycobacterium tuberculosis through colouring it in the sputum. There are two ways to test sputum for Mycobacterium tuberculosis : with a sputum smear and with a sputum culture. This is often done to help children cough up sputum. If a person has difficulty coughing up sputum, it can be induced by inhaling saline air through a mask., called a nebulizer. It is thicker than saliva and is usually coughed up. Sputum is a very thick bodily fluid (also called mucus), which comes from the lower airways. If that is the case, the bacterium can be found in sputum. In most cases, Mycobacterium tuberculosis infects the lungs (see 'Pulmonary Tuberculosis'). Where the bacterium is found depends on where the infection takes place. Instead,the diagnosis of active tuberculosis means finding the bacterium in a sample of bodily fluid from the patient. It can also not be excluded by a chest x-ray. The diagnosis of TB cannot be made by a chest x-ray alone. They are used to confirm a suspicion, and will always be followed by tests that aim at finding the TB bacterium. Therefore chest x-rays are usually an indicator of whether or not a person might have TB, but they cannot confirm the diagnosis.
If a health worker sees something on the lung, it can also be a lot of other things, and is not necessarily TB. TB cavities are often in these upper parts of the lung, also known as the apex ( apex is latin for 'the highest point'). The picture here shows a chest x-ray, and the arrow points to a TB cavity in the right upper part of the lung (in an x-ray, the right and left side are reversed). On a chest x-ray from someone with TB you can often see the cavitation that the TB bacteria form in the lung tissue. This allows the health worker to examine the lungs of the person with suspected TB. The first step to detecting TB infection, after taking a medical history and doing a physical exam, is to do a chest x-ray. For example a TB diagnostic with a sensitivity of 95% and a specificity of 99% would correctly identify 95 out of 100 people who have TB, but it would also incorrectly identify one of out 100 people who do not have TB. Good tests should have a sensitivity and a specificity at least above 90%. Sensitivity and specificity are expressed in percentages. A good diagnostic test is one with a high sensitivity (detects people with TB) and also a high specificity (correctly identifies healthy people without TB). No diagnostic test is ever completely foolproof – if thousands and thousands of people are tested, mistakes happen. If of the 100 people tested for TB, 50 people are healthy, then a test with a good specificity would correctly identify the 50 healthy people and show 50 negative results. Specificity means that a test only detects people with a disease, and does not wrongly detect a disease in somebody healthy.
In this case, health workers would speak of a test with a 'high sensitivity'. For example, if 100 people are being tested, and 50 of them have TB, then a good test should find all 50 people. Sensitivity means that a test needs to detect all people with a disease. The diagnosic tests for TB, as for all diseases, have to follow two important criteria of quality: sensitivity and specificity. Usually this is an infection of the lungs (pulmonary tuberculosis), it can be spread through droplets while coughing and sneezing. People can have TB even if the sputum culture results come back as negative.Īctive tuberculosis is an infection with Mycobacterium tuberculosis which can be transmitted to other people. The arrow shows the TB cavity in the upper part of the right lung.
0 kommentar(er)
