Sputum Test

Pulmonary tuberculosis

Dr. Nithin Jayan
Medically Reviewed by Dr. Nithin Jayan, MBBS, DNB
Last Updated on May 29, 2014
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Test : Pulmonary tuberculosis

Indications : A sputum examination is carried out on patients who show symptoms of TB.

Sputum collection is done early in the morning. The patient must have eaten at least two hours before the test. It is also essential to brush teeth and rinse mouth well prior to the test. It may be brought up by coughing (expectorated) or it may be or induced with the help of sterile saline or glycerine aerosol. The coughed up sputum is collected into a sterile cup provided by the laboratory.

Two forms of sputum tests are done simultaneously. A small sample of the sputum is taken and a smear is made on a glass slide. It is then stained using Gram stain. If the smear shows more number of normal cells then the sample collection has to be repeated and the experiment repeated for correct results. If plenty of WBCs are detected then an infection is indicated and the sample is cultured using an appropriate medium.

Physiology : Pulmonary tuberculosis (TB) is a contagious infection caused by Mycobacterium tuberculosis (M. tuberculosis). The infection primarily involves the lungs and eventually spreads to other organs. Mycobacteria are a group of non- motile, gram- positive bacteria that are capable of causing serious illnesses in humans.

The disease usually spreads through cough or sneeze droplets from contaminated persons, found in the air.

The TB bacterium has the ability to remain dormant for long periods of time as a result of which most people are symptomless when they become infected for the first time.

Those who are at risk include children, the elderly, the immune- compromised and those who are under nourished and live in crowded, unclean conditions.

Common symptoms of TB include cough, bloody sputum, fever, night sweats and weight loss.

Normal Range : Negative

Interpretation : If the culture results are positive for M. tuberculosis it is an indication that the patient is having TB.

References :

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joenie, Philippines

I had my x-ray positive but my sputum was negative and I never had a history of PTB, Am I still a PTB positive? kindly enlighten me thanks

requisoivy, Philippines

I had my x-ray and it have Upper right PTB.. and I had sputum test and its negative.. I tried 3x of sputum tes but still negative.. please advise..

gmichael0110, United States

if sputum is negative and had a history of tb before, is it possible that theres a recurrence? what other test sholuld be applied to know if its really positive...how about PPD?

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