The early signs of tuberculosis

Tuberculosis (TB) often starts quietly. The first symptoms are usually a cough that lasts more than three weeks, along with fatigue that doesn't improve with rest. You might feel tired even after sleeping, or notice you're short of breath during normal activities. These symptoms can feel like a lingering cold or mild flu, which is why many people don't suspect TB at first.

As TB progresses, the cough typically gets worse. You may cough up mucus, sometimes tinged with blood. Chest pain that worsens when you breathe or cough is common. Many people also develop a low fever, especially in the afternoon or evening, and night sweats that soak through clothing or sheets. Weight loss and loss of appetite often follow.

The tricky part: these symptoms develop slowly over weeks or months, not suddenly like flu. That gradual onset is one reason TB is sometimes missed. A cough lasting three weeks is the key marker—that's the point where doctors recommend testing rather than waiting to see if it passes.

Key Takeaways

  • A cough lasting longer than three weeks, especially with fatigue and low fever, is the main reason to get tested for TB.
  • TB symptoms develop slowly over weeks or months, not suddenly, so they're often mistaken for a lingering cold or bronchitis.
  • Night sweats, chest pain when breathing, and coughing up blood are warning signs that TB may be progressing.
  • You can have TB infection without symptoms (latent TB), so testing is important if you've been exposed to someone with active TB.
  • A skin test or blood test can detect TB infection; a chest X-ray confirms whether the infection is active in your lungs.

The difference between latent and active TB

TB infection comes in two forms, and only one causes symptoms. Latent TB means you carry the bacteria but your immune system is holding it in check. You have no symptoms, can't spread it to others, and may never know you're infected unless you're tested. About 25% of people with latent TB develop active disease later in life, usually when their immune system weakens.

Active TB is when the bacteria are multiplying and damaging your lungs. This is when you develop the cough, fever, and other symptoms described above. Active TB is contagious—you can spread it to others through the air when you cough or sneeze. This is the form that needs treatment right away.

You might have latent TB and feel completely normal. The only way to know is through testing. This matters because if you have latent TB and your immune system later weakens (from HIV, diabetes, or certain medications), the infection can become active. That's why people with latent TB are sometimes offered preventive treatment to stop it from progressing.

When to get tested for TB

You should consider TB testing if you have a cough lasting three weeks or longer, especially if you also have fever, night sweats, or are losing weight. You should also get tested if you've spent time around someone with active TB, even if you feel fine right now. Close contacts of TB patients are at highest risk and should be tested within a few weeks of exposure.

Certain situations increase your TB risk. People with HIV, those taking medications that suppress the immune system, people with diabetes, and those with a history of TB are tested more often. Healthcare workers, people living in crowded settings, and people who have recently moved from countries where TB is common are also tested routinely. If any of these apply to you, ask your doctor about testing even without symptoms.

Testing is straightforward and free or low-cost through public health departments in most places. Your doctor can order a test, or you can contact your local health department directly to find testing sites. There's no downside to getting tested—it's the only way to know for certain whether you have TB infection.

How TB testing works

Two main tests detect TB infection: the skin test (also called the Mantoux test or tuberculin skin test) and blood tests (called interferon-gamma release assays, or IGRAs). Both detect whether your immune system has been exposed to TB bacteria. Neither test is painful—the skin test is a small injection under the forearm, and blood tests are standard blood draws.

The skin test requires a follow-up visit 48 to 72 hours later to read the result. A nurse measures any swelling at the injection site. The size of the swelling, not redness, determines the result. Blood tests are faster—results come back in a few days. Both tests can show latent TB infection, but neither tells you whether the infection is active.

If either test is positive, your doctor will order a chest X-ray to see whether TB is active in your lungs. The X-ray looks for the characteristic pattern of TB damage. If the X-ray is normal, you have latent TB. If it shows signs of lung damage, you likely have active TB and need treatment. Your doctor may also test a sputum sample (mucus you cough up) to confirm active TB and check which medications will work best.

Symptoms that need urgent attention

Most TB symptoms develop slowly, but some changes mean you should seek care quickly. Coughing up blood, even small amounts, warrants a same-day call to your doctor. Severe chest pain, difficulty breathing, or confusion can signal that TB has spread or that a complication has developed. Fever above 103°F (39.4°C) is also worth reporting promptly rather than waiting for a routine appointment.

If you've already been diagnosed with TB and are on treatment, watch for side effects from the medications. TB drugs can cause nausea, vomiting, yellowing of the skin or eyes, or numbness in the hands and feet. These don't mean you should stop taking the medication, but they do mean you should contact your doctor to adjust your dose or switch to a different drug. Staying on treatment is critical—stopping early allows the bacteria to develop resistance.

What happens after a positive test

If you test positive for TB infection, your doctor will determine whether it's latent or active. For latent TB, you'll likely be offered preventive treatment—usually a single antibiotic taken daily for several months. This prevents the infection from becoming active later. Preventive treatment is especially important if you have HIV, are a young child, or have other conditions that weaken immunity.

If you have active TB, treatment involves taking multiple antibiotics together for at least six months. The standard regimen uses four drugs for the first two months, then two drugs for the remaining four months. It's crucial to take all the medications exactly as prescribed, even after you start feeling better. Stopping early allows resistant TB to develop, which is much harder to treat.

During treatment, you'll have follow-up appointments to check your progress and watch for side effects. Your doctor may repeat chest X-rays or sputum tests to confirm the infection is clearing. Most people with active TB stop being contagious after about two weeks of treatment, though they need to continue the full course to be cured.

Why TB symptoms are easy to miss

TB mimics other common illnesses, which delays diagnosis. A persistent cough might seem like bronchitis or asthma. Fatigue and weight loss could look like depression or a thyroid problem. Night sweats happen with many conditions—menopause, lymphoma, chronic infections. Because TB develops slowly, people often assume they'll get better on their own and don't seek testing.

Geography matters too. In countries where TB is rare, doctors may not think of it first. Someone with a three-week cough might be treated for asthma or acid reflux before anyone considers TB. This is why mentioning your symptoms directly—especially a cough lasting more than three weeks—helps your doctor think of the right tests.

Another reason TB is missed: you can feel reasonably well with active TB, at least at first. Unlike flu, which makes you feel acutely sick, TB lets you function for weeks or months while the bacteria slowly damage your lungs. By the time symptoms become severe, significant lung damage may have already occurred. This is why testing based on symptom duration, not symptom severity, matters.

Frequently Asked Questions

Can you have TB without any symptoms?

Yes. Latent TB infection causes no symptoms and you won't know you have it without testing. About 25% of people with latent TB eventually develop active disease, usually years later when their immune system weakens. This is why testing is important if you've been exposed to someone with active TB, even if you feel fine.

How long does a TB cough last if untreated?

A TB cough typically lasts weeks to months and gradually worsens. Without treatment, active TB can cause severe lung damage and spread to other organs. This is why testing at three weeks of cough is important—waiting longer increases the risk of complications and the chance you'll spread it to others.

Can you catch TB from someone with latent TB?

No. Only active TB is contagious. People with latent TB have no symptoms and can't spread the bacteria to others. You can only catch TB from someone with active TB, usually through breathing in air they've coughed or sneezed into.

What if the TB skin test is negative but you have symptoms?

A negative skin test usually means you don't have TB infection, but it's not perfect. People with HIV, severe malnutrition, or recent TB exposure can have false negatives. If you have a three-week cough and a negative skin test, your doctor may order a blood test or chest X-ray to be certain, or repeat testing after a few weeks.

How soon after exposure should you get tested for TB?

If you've been exposed to someone with active TB, get tested within two to eight weeks. Testing too early (within the first two weeks) may miss a new infection. Your doctor may recommend a repeat test after eight weeks if the first test is negative, since the immune response takes time to develop.