Diagnosis and Treatment
The steps to diagnose TB infection and disease include:
- A medical evaluation that includes history and risk assessment
- The tuberculin skin test or quantiferon exam
- A chest x-ray
- A bacteriological examination
The Medical History
The medical history includes facts about the social, family, medical, and occupational aspects of the patient's life. The clinician should ask about:
- Exposure to a person who has infectious TB
- Any symptoms of TB (productive cough longer than 3 weeks, fever, unexplained weight loss, night sweats)
- The patient's history of TB infection or TB disease
- Risk factors for developing the disease (intravenous drug use, immune system condition, diabetes)
- Country of birth
- Length of time in the United States if the patient is an immigrant
The Tuberculin Skin Test
The tuberculin skin test is used to determine if a person has TB infection. A substance, called tuberculin, is injected into the skin. Tuberculin is purified protein and not a vaccine or contains any germ cells. The immune system of most people who have TB infection recognizes tuberculin and this will cause a reaction in the skin.
The Mantoux method of application is the preferred type of skin test because it is the most accurate. When the Mantoux skin test is performed, a needle is injected into the upper skin layer of the patient's arm. The arm is examined 48 to 72 hours after the tuberculin injection in order to evaluate the reaction on the patient's skin. Any swelling that can be felt around the site of the injection, also known as induration, is measured. The diagnosis of TB infection depends on the size of the measured induration and the patient's individual risk factors.
Quantiferon Exam
In December 2004, the FDA approved a new diagnostic test for M. tuberculosis-complex infection known as the Quantiferon®-TB Gold. This in vitro diagnostic test measures the amount of interferon-gamma produced by cells in whole blood that have been stimulated by mycobacterial peptides. The peptides used in the test mimic proteins known as ESAT-6 and CFP-10, which are present in M. tuberculosis but absent from all BCG strains and from most non-tuberculosis mycobacteria. It is intended for use as a diagnostic aide for M. tuberculosis infection, including both tuberculosis disease and latent tuberculosis infection (LTBI). It cannot distinguish between LTBI and tuberculosis disease, and should be used in conjunction with risk assessment, radiography, and other diagnostic evaluations. The advantages of Quantiferon®-TB Gold and the prior generation test, compared with the tuberculin skin test, are that results can be obtained after a single patient visit, and that, because it is a blood test which is performed in a qualified laboratory, the variability associated with skin test reading can be eliminated.
An additional advantage of this newer generation blood test is that the test is not affected by past BCG vaccination, and will eliminate the unecessary treatment of patients with BCG-related false positive results. Furthermore, the Quantiferon®-TB Gold does not affect the result of future Quantiferon®-TB Gold tests (i.e. no "boosting," as with the TST). However, the performance of Quantiferon®-TB Gold has not been sufficiently evaluated in all patient groups. Multiple studies are underway to determine the accuracy of the test in predicting progression to active TB.
A Chest X-Ray
If TB infection or disease is suspected, a chest x-ray should be taken. The chest x-ray helps the clinician determine any presence of TB or old healed TB disease. In TB infection, the chest x-ray is usually normal.
A Bacteriological Examination
This is an examination of the secretions from the lungs (sputum), directly under a microscope or by culture.
Treatment of TB Disease
The treatment for TB disease usually lasts 6 months and requires 4 or more medications. Most of the bacilli are killed during the first 8 weeks of treatment. If the entire treatment course is not completed, some bacilli may survive and cause TB disease at a later time or develop into a strain of drug-resistant TB.
The initial recommended treatment for TB disease includes 4 medications taken simultaneously:
- Isoniazid (INH)
- Rifampin (RIF)
- Pyrazinamide (PZA)
- Ethambutol (EMB) or streptomycin (SM)
- Treatment of Latent TB Infection
The purpose of treating latent TB infection is to prevent future disease from developing. The treatment requires 6-9 months of a single medication. Failure to take the complete course to treat TB infection will not confer the desired lifetime protection against TB disease. LTBI treatment options are detailed in the revised CDC Update: Adverse Event Data and Revised American Thoracic Society/CDC Recommendations Against the Use of Rifampin and Pyrazinamide for Treatment of Latent Tuberculosis Infection---United States, 2003 ( http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5231a4.htm).
For more information, view the Centers for Disease Control's BBasic TB Facts.