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How is tuberculosis diagnosed?

A complete medical evaluation for tuberculosis includes a medical history, a physical examination, a tuberculin skin test, a chest X-ray, and microbiologic smears and cultures. The medical history includes obtaining the symptoms of pulmonary tuberculosis: productive, prolonged cough of three or more weeks, chest pain, and hemoptysis. Systemic symptoms include fever, chills, night sweats, appetite loss, weight loss, and easy fatigability. Other parts of the medical history include prior

tuberculosis exposure, infection or disease; past tuberculosis treatment; demographic risk factors for tuberculosis; and medical conditions that increase risk for tuberculosis disease such as HIV infection. Tuberculosis should be suspected when a persistent respiratory illness in an otherwise healthy individual does not respond to regular antibiotics.

Latent tuberculosis infection can be detected with a tuberculosis skin test, which can be obtained at the health department or a doctor’s office. The test involves injecting a small amount of testing fluid (called tuberculin) just under the skin on the lower part of the arm. After two or three days, the reaction to the testing fluid will be measured. If there is a small bump where the tuberculin was injected, it will be measured to find out if the test reaction is positive or negative. A positive reaction usually indicates a latent tuberculosis infection.

Often, the first indication of tuberculosis is an abnormal chest x-ray or other test result rather than physical discomfort. On a chest x ray, evidence of the disease appears as numerous white, irregular areas against a dark background, or as enlarged lymph nodes. The upper parts of the lungs are most often affected. A PPD test is always done to show whether the patient has been infected by the tubercle bacillus. To verify the test results, the physician obtains a sample of sputum or a tissue sample (biopsy) for culture. Three to five sputum samples should be taken early in the morning. If necessary, sputum for culture can be produced by spraying salt solution into the windpipe. Culturing M. tuberculosis is useful for diagnosis because the bacillus has certain distinctive characteristics. Unlike many other types of bacteria, mycobacteria can retain certain dyes even when exposed to acid. This so-called acid fast property is characteristic of the tubercle bacillus.

Body fluids other than sputum can be used for culture. If tuberculosis has invaded the brain or spinal cord, culturing a sample of spinal fluid will make the diagnosis. If tuberculosis of the kidneys is suspected because of pus or blood in the urine, culture of the urine may reveal tubercular infection. Infection of the ovaries in women can be detected by placing a tube having a light on its end (a laparoscope) into the area. Samples also may be taken from the liver or bone marrow to detect the tubercle bacillus.

More information on tuberculosis

What is tuberculosis? - Tuberculosis (TB) is a contagious, wasting disease characterized by the coughing up of mucus and sputum, fever, weight loss, and chest pain.
How is tuberculosis transmitted? - Tuberculosis is spread through air droplets which are expelled when persons with infectious TB disease cough, sneeze, speak, or sing.
What causes tuberculosis? - Tuberculosis is caused by the bacterium Mycobacterium tuberculosis. Transmission occurs only from persons with active TB disease.
What're the risk factors for tuberculosis? - Tuberculosis is more common in elderly persons. The risk of tuberculosis increases when the immune system is unhealthy.
What are the symptoms of tuberculosis? - Symptoms of tuberculosis include cough, sputum, bleeding from the lungs, fever, night sweats, loss of weight, and weakness.
How is tuberculosis diagnosed? - Diagnosis of tuberculosis includes a medical history, a physical examination, a tuberculin skin test, a chest X-ray, and microbiologic smears and cultures.
What's the treatment for tuberculosis? - Directly observed treatment is effective in eliminating the problem of noncompliance. Surgical treatment of tuberculosis may be used if medications are ineffective.
How to prevent tuberculosis? - Preventive measures for tuberculosis include strict standards for ventilation, air filtration, and isolation methods. Preventive antibiotic treatment may have to be given.
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