Tuberculosis - Diagnosis

The first sign of tuberculosis may be the presence of one or more of the symptoms described. For example, someone who experiences persistent cold-like systems might seek medical advice. In such cases, a medical worker can take samples of a person's sputum. The sputum can then be cultured (grown and studied) to look for tubercle bacilli. Standard chemical tests are available for the detection of these bacilli.

Body fluids other than sputum can also be collected and cultured. For example, studies of the urine will indicate whether the kidneys or bladder have been infected.

Perhaps the most common warning sign for tuberculosis is an abnormal chest X ray. The X ray of a person with pulmonary tuberculosis will show numerous white, irregular areas against a dark background and/or enlarged lymph nodes. Chest X rays are recommended for anyone who has close contact with a TB patient. For example, health care workers who have contact with people at risk for the disease should have regular chest X rays.

The most common method for diagnosing TB has traditionally been a tuberculin skin test. Tuberculin consists of antigens, substances produced by an M. tuberculosis culture. In a tuberculin skin test, these antigens are injected beneath the skin. If TB bacteria are present, the injection becomes hard, swollen, and red within one to three days. This change is generally a good indication that infection has occurred.

Today, skin tests generally use a substance called purified protein derivative (PPD). The PPD test, also called the Mantoux test, tends to provide more accurate results than the traditional tuberculin test. However, both false positives and false negatives do occur. A false positive is a test that suggests infection has occurred when it really has not. A false negative is a test that shows that no infection has occurred when, in fact, it actually has.