A positive tuberculosis (TB) test result indicates an interaction with the bacteria that causes this infection. Individuals undergo TB testing for various reasons, including potential exposure, certain health conditions, or occupational requirements. Understanding what a positive result signifies is important, as it does not always mean an individual has active, contagious disease.
Understanding a Positive Result
A positive TB test, whether a skin test (TST) or a blood test (IGRA), indicates infection with Mycobacterium tuberculosis bacteria. The TST involves injecting a small amount of protein under the skin and measuring the reaction, while an IGRA tests a blood sample for an immune response. Both tests show the immune system has recognized the bacteria.
However, a positive result does not automatically mean active TB disease. Most people with a positive test have latent TB infection, where the bacteria are present but inactive. Further medical evaluation is necessary to distinguish between latent infection and active disease.
Distinguishing Latent Infection from Active Disease
The distinction between latent TB infection (LTBI) and active TB disease is important for both individual health and public health. In latent TB infection, the Mycobacterium tuberculosis bacteria are present in the body but remain inactive or dormant. Individuals with LTBI typically experience no symptoms and cannot spread the bacteria to others. Their immune system usually contains the bacteria, preventing them from multiplying and causing illness.
Active TB disease occurs when the bacteria multiply, causing noticeable symptoms and potentially leading to illness. People with active TB disease often feel sick and may be able to spread the bacteria to others, especially if the infection is in the lungs or throat. Common symptoms of active TB include a cough lasting more than three weeks, chest pain, coughing up blood or mucus, fatigue, weight loss, loss of appetite, fever, chills, and night sweats. While TB most commonly affects the lungs, it can also spread to other parts of the body, such as the kidneys, spine, brain, or lymph nodes, leading to varied symptoms depending on the affected area.
Next Steps After a Positive Test
Following a positive TB skin or blood test, a healthcare provider will conduct additional evaluations to determine if the infection is latent or active. This process typically begins with a thorough medical history review and a physical examination. The healthcare provider will inquire about any symptoms, past exposures, and other health conditions that might influence the diagnosis.
A chest X-ray is a standard follow-up test to look for signs of active TB disease in the lungs. Abnormalities on the chest X-ray may suggest active disease, prompting further investigation. If active TB disease is suspected, particularly in the lungs, sputum smear and culture tests are often performed. These tests involve collecting samples of mucus coughed up from the lungs to identify the presence of TB bacteria and determine their drug susceptibility.
Treatment and Management
Treatment for a positive TB test result depends on whether the individual has latent TB infection or active TB disease. For latent TB infection (LTBI), the goal of treatment is to prevent the inactive bacteria from becoming active and causing illness. Preventive treatment typically involves taking one or two types of antibiotics for a shorter duration, often ranging from three to nine months. Commonly used medications for LTBI include isoniazid, rifampin, or rifapentine. Completing the full course of medication is important to reduce the risk of developing active disease in the future.
If active TB disease is diagnosed, a more intensive treatment regimen is required. This usually involves a combination of several different antibiotics taken over a longer period, typically four to nine months. Common medications for active TB include isoniazid, rifampin, pyrazinamide, and ethambutol. It is important to adhere strictly to the prescribed medication schedule and complete the entire course of treatment, even if symptoms improve, to ensure all bacteria are eliminated and to prevent the development of drug-resistant TB. In some cases, directly observed therapy (DOT), where a healthcare worker observes the patient taking their medication, may be recommended to ensure adherence.