Sputum test for tuberculosis

, medical expert
Last reviewed: 06.11.2022

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Pulmonary tuberculosis is an infectious disease caused by Koch's bacilli. In the first stages, the infection may be asymptomatic, with time fatigue, lethargy, sweating, pallor of the skin appear, and a low temperature persists. In the course of the development of the disease, a cough begins, initially dry, then with sputum discharge - a pathological secret, indicating damage to the tissues of the organ.

What is sputum for tuberculosis?

Based on the color of the sputum, one can make an assumption about the diagnosis, but a serious examination is required for a final conclusion. With pathologies of the lower respiratory tract, it can vary from colorless or white to canary, yellow-green, green, and also with blood fragments.

Tuberculosis in the initial stages is characterized by transparent glassy sputum, white indicates the formation of protein and deeper tissue damage, brown, orange-brown with a hint of rust - the destruction of blood vessels.

Purulent sputum is yellowish-greenish in color, indicating the progression of the disease, in which pus is separated. In severe cases, in the last stages of tuberculosis, blood is found in it, and sometimes only blood is coughed up, which is a sign of internal bleeding.

There is another course of tuberculosis, when the accumulation of sputum is not accompanied by a cough. They are concentrated in the throat, creating a feeling of a lump, causing an unpleasant tickle and a desire to get rid of, but there is no cough.

Sputum test for tuberculosis

A blood test for suspected tuberculosis shows only some abnormalities, such as elevated ESR, anemia, leukopenia. This requires a sputum test. What are the methods? [1]

The analysis of the secret for tuberculosis includes studies:

  • macroscopic (the volume of the allocated secret, its color, smell, layering, impurities is determined);
  • microscopic (to detect acid-resistant bacteria);
  • bacterioscopic (for Mycobacterium tuberculosis - MBT).

Sputum collection for tuberculosis

You can take sputum for the detection of tuberculosis both in public medical institutions and in private laboratories with a referral from a doctor. There is a certain algorithm. So, to detect mycobacteria, you will need to collect three samples.

For the first, the patient is given a pocket spittoon equipped with a label that indicates the name, date of birth and collection. Before the procedure, rinse your mouth with water to remove food debris. The container must be brought to the mouth, take 3 deep breaths and cough strongly, spitting sputum into the container. The laboratory assistant, making sure that there is a sufficient volume of material (3-5 ml), closes it tightly with a lid and places it in a box for transportation.

The patient is given another spittoon with him for self-collection of the analysis on the morning of the next day after brushing his teeth, which he himself delivers to the medical facility. There is also one last test. [2]

Part of the sputum is sent to the laboratory tank for culture, this method is much more sensitive than the previous one, because can detect even a single mycobacterium.

How long does a sputum test for tuberculosis take?

A complete sputum analysis is done 3 months. Such a long period is explained by the fact that tubercle bacilli can grow very slowly. There are also quick methods that still last at least 42 days.

Bacterioscopy of sputum in tuberculosis is simple and economical, but takes a long time.

PCR sputum for tuberculosis

The polymerase chain reaction (PCR) method is very accurate. It detects the presence of a virus with 100% certainty, when other tests with a small number of mycobacteria can give a negative result. It is based on the detection of bacterial DNA in the samples taken.

Under the influence of enzymes and temperature (from 50º to 95ºС), two DNA molecules are formed from one DNA molecule. It takes 3 minutes. To get the result, 30-40 cycles are enough, which means one and a half to two hours. The PCR method detects tuberculosis at the earliest stages of its development.

Microscopic examination of sputum in tuberculosis

Microscopic examination of sputum reveals eosinophils - one of the subtypes of leukocytes, a large number of erythrocytes in pulmonary bleeding, elastic fibers, Kurshman's spirals, Ehrlich's tetrad.

Despite the fact that in nature there are many acid-resistant bacteria other than tuberculosis, nevertheless, this is one of the main methods for determining tuberculosis, because. Differs in simplicity and speed (from one hour). Microscopic examination of sputum makes it possible to identify the most dangerous patients for surrounding patients, as well as to trace the dynamics of treatment. [3]

Sputum result for tuberculosis

A positive sputum test result means that Koch's bacillus has been detected and this confirms the diagnosis. Negative indicators do not exclude it and require other studies: tuberculin test, enzyme immunoassay, histological, fluorography, radiography, computed tomography.

How is the sputum of pneumonia different from tuberculosis?

With pneumonia, mucous and mucopurulent sputum is most often observed, but blood impurities can be not only with tuberculosis, but also with focal pneumonia. The orange-brown color is inherent in both lobar pneumonia and tuberculosis.

Both pathologies are characterized by fibrinous clots in the sputum, but with pneumonia there are no rice-shaped bodies (Koch lenses), less protein and bile can be detected.

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