Diagnosis of Tuberculosis
Because of the long time span between infection with the bacterium and the outbreak of tuberculosis (latency period, incubation period), it is often difficult for the attending physician to detect indications of a tuberculosis infection in the medical history (medical record). It is not uncommon for false diagnoses to occur because the possibility of tuberculosis is not taken into consideration. The diagnosis of tuberculosis is quite difficult, because there is no simple test that works reliably.
Rather, one tries to increase the certainty of a correct diagnosis through several tests. The first indications are possible contact with tuberculosis patients, for example through sick relatives, trips abroad to countries with a low socio-economic status (especially former Eastern Bloc countries) or signs of reduced immune function of the body. Blood tests also do not reveal typical values for or against tuberculosis.
Often signs of a general inflammatory reaction are found, such as an increased SLA (blood cell lowering rate) or slight shifts in the blood count. The so-called tuberculin test (Mendel-Mantoux test) is used to check whether the patient has had contact with mycobacteria before. For this purpose, the patient is injected with tuberculin (a protein of the tuberculosis pathogens) into the forearm flexor.
If the patient has already been infected with the bacteria in the past, the injection site will redden and swell within two to three days. If this swelling exceeds a certain level, a previous infection can be assumed. Possible false-negative results (infected people who are wrongly not recognized) are often found when: A positive test is not proof of tuberculosis, but at least a strong suspicion.
An X-ray image of the patient’s chest (X-ray thorax) is now taken. There one looks for the typical signs of tuberculosis, for calcified granulomas in the lungs. However, the X-ray image does not offer any certainty either, since neither a negative finding excludes tuberculosis nor a positive finding proves tuberculosis.
The next step in the diagnosis of tuberculosis is the attempt to detect the bacteria directly. For this purpose, various samples are taken from the patient: Urine, gastric juice, bronchial secretion by lung endoscopy or saliva. One tries to cultivate the bacteria from this material.
If the cultivation is successful, this is evidence of a tuberculosis infection. Cultivation takes several weeks due to the slow reproduction rate of the bacteria. This is problematic for two reasons: In rare cases, an MRI of the lung can provide information, as the MRI of the lung can show soft tissue processes within the lung well.
- The infection occurred less than seven weeks ago, when the body is not yet able to trigger an appropriate immune response.
- The patient suffers from an immune deficiency (HIV-infected, immunosuppressive (=defense-weakening to -suppressing) treatment, leukemias).
- Has been recently vaccinated.
- Does the patient have to endure a long period of uncertainty and
- The possible risk of spreading the bacteria must be considered.
