How tuberculosis shows up in your body

Tuberculosis (TB) usually announces itself through a cough that lasts more than three weeks. This is the single most common sign. The cough may start dry and then produce mucus or phlegm, sometimes tinged with blood. You might also feel chest pain when you breathe or cough.

Beyond the cough, TB often brings fatigue that doesn't improve with rest, fever that tends to be worse in the afternoon or evening, and night sweats so heavy you wake up drenched. You may lose weight and appetite without trying. These symptoms develop slowly—sometimes over weeks or months—which is why people often don't realize something serious is happening until the cough has been there for a while.

Not everyone with TB has all these signs. Some people have only a cough. Others have fever and weight loss but no cough at all. The symptoms depend partly on which form of TB you have: active TB disease (the kind that makes you sick and can spread to others) causes noticeable symptoms, while latent TB infection (TB bacteria in your body that aren't multiplying) causes no symptoms at all.

Key Takeaways

  • A cough lasting more than three weeks, especially one that produces mucus or blood, is the most common sign of active TB disease.
  • Fever, night sweats, fatigue, and weight loss often appear alongside the cough and develop slowly over weeks or months.
  • A doctor diagnoses TB using a skin test, blood test, or chest X-ray—not by symptoms alone, since TB symptoms look like many other illnesses.
  • If you have a persistent cough or TB symptoms, see a doctor as soon as you can; TB is treatable but spreads through the air when left untreated.
  • Latent TB infection causes no symptoms, so you only know you have it if you've been tested after exposure to someone with active TB.

Why you need a test, not just symptoms

A three-week cough could be TB, but it could also be bronchitis, pneumonia, asthma, or a lingering viral infection. Fever and night sweats happen with flu, other infections, and some cancers. Because TB symptoms mimic so many other conditions, doctors cannot diagnose it by listening to your story or examining you—they need a test.

This is important because it means you should not assume you have TB based on how you feel, and you should not assume you don't have it just because your symptoms seem mild. The only way to know is to see a doctor and get tested.

The three main tests doctors use

The tuberculin skin test (also called the Mantoux test) is the oldest and still most common screening tool. A nurse injects a small amount of TB protein under the skin on your forearm. You come back 48 to 72 hours later, and the nurse measures any bump or hardening that formed. A bump of a certain size means TB bacteria are in your body—though this test alone cannot tell whether you have active TB or latent TB infection.

The blood test (called an interferon-gamma release assay, or IGRA) detects TB infection by measuring how your immune cells react to TB proteins in a lab. It requires one blood draw and gives results in a few days. This test is more specific than the skin test and works better in people who have received the BCG vaccine (common outside the United States).

A chest X-ray is usually the next step if either the skin test or blood test comes back positive. The X-ray shows whether TB bacteria have damaged your lungs. If the X-ray looks normal, you likely have latent TB. If it shows patches, cavities, or other damage in the lungs, you likely have active TB disease. A doctor may also ask you to cough up sputum (mucus from deep in your lungs) so it can be tested under a microscope or sent for culture to confirm TB and check which medicines will work against it.

What happens after a positive test

If your skin test or blood test is positive, your doctor will order a chest X-ray. If the X-ray is normal and you have no symptoms, you have latent TB infection. This means TB bacteria are in your body but not making you sick, and you cannot spread it to others. Your doctor will likely recommend treatment with one or more TB medicines to prevent the infection from becoming active later.

If the X-ray shows lung damage or you have TB symptoms, you have active TB disease. Your doctor will send sputum samples to the lab to confirm TB and test which medicines work best. You will start a course of TB medicines—usually a combination of four drugs taken for two months, followed by two drugs for four more months. During the first two weeks of treatment, while you're on the strongest medicines, you're still contagious, so you'll need to stay home and avoid close contact with others.

Active TB is serious if left untreated, but it responds well to medicine. Most people who take their medicines as prescribed are no longer contagious after two to three weeks and are cured after completing the full course.

When to see a doctor

See a doctor if you have a cough that lasts more than three weeks, even if you don't have fever or other symptoms. Also see a doctor if you have fever and night sweats lasting more than a few weeks, or if you've lost weight without trying and feel unusually tired.

If you know you've been in close contact with someone who has active TB—a family member, coworker, or person you live with—tell your doctor that when you call. You may need testing even if you have no symptoms, because TB can take weeks or months to show up after exposure.

If you're coughing up blood, have severe chest pain, or feel short of breath, seek care the same day if possible. These are not always TB, but they need prompt attention.

Risk factors that make TB more likely

Certain situations make you more likely to develop active TB if you're exposed to the bacteria. These include living with someone who has active TB, having HIV or another condition that weakens your immune system, taking medicines that suppress immunity, having diabetes, or being very malnourished. People who are homeless, incarcerated, or living in crowded shelters also face higher risk.

If any of these apply to you and you develop a cough or other TB symptoms, mention it to your doctor. It helps them decide how quickly to test you and how carefully to look for TB.

The difference between latent and active TB

Latent TB infection means TB bacteria are dormant in your lungs or lymph nodes. You feel fine, have no symptoms, and cannot spread TB to anyone else. About 5 to 10 percent of people with latent TB will develop active disease at some point in their lives, usually within the first two years after infection. The risk is much higher if your immune system is weak.

Active TB disease means the bacteria are multiplying and damaging your lungs. You have symptoms, you can spread TB to others through coughing or sneezing, and you need treatment right away. The difference is crucial because latent TB is treated to prevent it from becoming active, while active TB is treated to cure the disease and stop transmission.

Frequently Asked Questions

Can you have TB without a cough?

Yes. Some people with active TB have fever, night sweats, and weight loss but no cough, especially early on. This is less common than a cough, but it happens. If you have unexplained fever or night sweats lasting weeks, see a doctor and mention TB as a possibility.

How long does it take to get TB test results?

A skin test requires two visits: one to place the test and one 48 to 72 hours later to read it. A blood test (IGRA) takes one visit and results come back in a few days. A chest X-ray is done the same day. If sputum samples are sent to the lab, results can take one to two weeks.

What if I was exposed to TB but have no symptoms?

You should still be tested, because TB can take weeks or months to show symptoms. If you test positive and have no symptoms, you have latent TB infection and will be offered treatment to prevent it from becoming active.

Can you catch TB from someone with latent TB?

No. Only people with active TB disease spread TB to others, and only through the air when they cough, sneeze, or speak. People with latent TB infection cannot spread it.

Is TB curable?

Yes. Active TB is curable with a six-month course of medicines. Latent TB is prevented from becoming active with medicine. The key is taking all your medicines exactly as prescribed, even after you feel better.