Key methods of TB diagnostics:
- Microbiological diagnostics
- X-ray diagnostics
- Tuberculin diagnostics
There are two key methods of microbiological TB diagnostics:
- Microscopy of sputum smear;
- Bacteriological sputum analysis.
Importance of microbiological research method:
- The most effective for early TB diagnostics;
- The most effective for TB diagnosis verification;
- Allows to watch the clinic development and treatment efficiency
- Allows to assess the level of patient's bacillus excretion
- Defines contagiousness.
Why are the patients coughing for more than 3 weeks offered to make sputum analysis examination:
- Coughing for more than 3 weeks can be a TB indication
- Allows to detect the most dangerous forms of TB. The more mycobacteria in sputum the more contagious the patient is and the bigger threat he is for the other people.
- Sputum smear microscopy is a safe and simple method of TB detection for a patient.
Rules for collection of sputum for microbiological examination:
It's very important to collect sputum and not saliva! It's important to have at least 3 portions collected at different times within 2 days.
- Sputum shall be collected in a medical institution in a specially equipped room.
- At home sputum shall be collected in the open air at a distance of other people
- The collected sputum sample shall be delivered to a medical institution as soon as possible.
- Prior to sputum collection rinse mouth with water to remove food particles and contaminating microflora of oral cavity (the exception is the morning collection of sputum at home prior to which you should brush your teeth)
- Take two deep breaths and hold the air for several seconds after each breath and slowly breathe out. Take the third breath and breathe out vigorously. Then take another deep breath and cough hard.
- Place the open container as close as possible to the mouth and spit the sputum, which came up in your mouth.
- Screw the cap tightly.
- Wash hands with soap.
What are the other methods of TB diagnostics?
Chest X-ray is one of TB diagnostics methods. Most frequently Chest X-radiography examination is used as it:
- helps detect the disease since about 80-85% of patients suffer from TB in lungs;
- in most cases detects pathology of people with TB in lungs;
- defines the disease site and prevalence. However, without taking into account the results of other examinations it cannot serve as a reliable diagnostics method as abnormalities resembling TB can be caused by a variety of other illnesses of respiratory organs. Nowadays, the clinical course of many diseases including TB has changed and there is not an absolutely typical X-ray TB picture;
Although an abnormality on a chest x-ray may lead a clinician to suspect TB, it's important to remember that the results of a chest x-ray cannot confirm that a person has TB disease. The results shall be supported by a smear microscope test and bacteriologic sputum investigation.
- additional X-ray methods are used to define the nature of the process, its structure and decomposition areas: tomography, computed tomography, magnetic resonance image.
What is the role of periodic mass photofluorographic examinations of population in TB detection?
Most TB cases with intensive bacteria excretion develops within a shorter period of time as compared with possible time intervals between photofluorographic examinations. In addition, 90% of people who develop TB soon start experiencing coughing, fever, loss of weight, and coughing up of sputum. That's why TB in most cases is detected not during photofluorographic examinations but earlier when people approach the district clinician and take sputum examination.
Why is it recommended not to arrange mass photofluorographic examinations of population:
even if examinations are arranged in the best way possible?
- This method allows us to detect just some new cases of TB
- It's impossible to examine all the population
- The risk groups are not included - unemployed, alcoholics and drug addicts, homeless people, etc.
- Despite past practice of mass photofluorographic examinations 30-40% of all new TB cases were detected on the basis "medical aid appealability"
- It has little influence upon the frequency of registration of "contagious" forms of TB as such forms develop fast enough to fit the intervals between photofluorographic examinations
- The method is expensive and requires lots of expensive equipment, qualified skilled technical and medical staff to ensure constant servicing
- It requires special conditions to install and operate the equipment. X-ray equipment and transportation means often break down and stay idle for months
- Harmful for patients' health
Tuberculin diagnostics - skin PPD test
PPD test (tuberculin test, tuberculin diagnostics) is a method of investigation of the body reaction to injection of a special medication - tuberculin.
Tuberculin diagnostics background
PPD test is more than 100 years old. Tuberculin was invented in 1880 by a German doctor Robert Koch, who discovered the TB bacillus named after him. At first tuberculin was applied onto the skin specially injured for this purpose. In 1907 Australian doctor K. Pirke offered to scratch skin with a special steel feather (scarificator) and drop tuberculin on it. A little later a French Dr. Mantu offered intradermal injection of tuberculin, which was introduced in 1909 and in the USSR - in 1975.
What is tuberculin?
Tuberculin is a mixture of organic matters produced from TB microbacteria.
Why is PPD test needed?
PPD test is needed to:
- To diagnose newly-detected TB patients that is those who were detected as TB infected for the first time;
- To diagnose TB infected people who do not have any symptoms of the disease, and TB diagnosis verification;
- Selection of children for revaccination;
- To diagnose TB patients who live with HIV/AIDS (see Tuberculosis/AIDS- co-infection).
How are the PPD test results assessed?
2-3 days after injection of tuberculin the test site is raised and feels hard to the touch - the so called papule. It looks like a raised bump under the skin's surface. If you palpate the area using a transparent ruler (or if you palpate it with a gentle stroking with a finger) the reaction site shall get a little white. In contrast to usual redness (although you can't always measure it with a finger) papule is harder in consistency by palpation as compared with the rest skin. The papule size is measured with a transparent ruler (to see the maximum diameter of induration) 72 hours after injection of tuberculin; the adequate lighting to be provided. A reaction is measured in millimeters in hard swelling. Redness around the hard swelling does not mean immune to TB or TB infection itself. However the results shall be recorded if there is not induration. All persons with positive Mantoux reaction shall be subject to other means of examination regardless of previous BCG vaccination.
What is Mantoux reaction?
Reaction of body to tuberculin is a kind of allergy reaction. At the place of injection tuberculin produces inflammation as the result of mycobacteria fragments (which are in tuberculin) stimulating lymphocytes (protection cells) from skin blood vessels. But only TB sensitive lymphocytes get into reaction.
Caring for the test site
You should avoid using antiseptic solutions or hydrogen peroxide until assessment of the results. You should not cover the spot with plaster as it could lead to sweating. Don't let your child rub the test site. Please, remember that any manipulation of the test site could alter the test!!!
Mantoux shall not be performed in case of
- Skin diseases;
- Acute or chronic infections and exacerbation of somatic diseases (Mantoux test shall be performed 1 month after all the clinic symptoms disappear or just after release from quarantine);
- Any allergy reactions within one month after any vaccination;
Mantoux test and vaccination:
Mantoux test shall not be performed at the same day with vaccination as it increases the risk of false positive results. Vaccination shall be made after the results are administered.
In case vaccination is made prior to Mantoux test then in order to avoid interference the time interval between injection of inactivated vaccines such as vaccines against flu, diphtheria, tetanus, etc. and Mantoux test shall be no less than 4 weeks. The same goes to injection of serum and antibodies. In case of live vaccine (measles, parotiditis and German measles) the time interval shall be increased to 6 weeks.