A negative TB test means there is no bump or only a very small bump (less than 5mm) at the spot where the test fluid was put into your skin. This good news usually shows you don’t have TB germs in your body.

This guide will help you know what to look for after your TB test, understand what negative results mean, and learn when you might need more testing. We’ll also cover why some people get false results and what to do next.

How To Tell If Your TB Test Is Negative

What You’ll See On Your Arm

When you have a negative TB skin test, there is no bump or only a very small bump at the injection site. Here’s what to look for:

Normal Negative Results:

• No raised bump at all
• Very small bump less than 5 millimeters wide
• Little to no redness around the test spot
• The skin looks almost the same as before the test

Your healthcare provider will measure any firm, raised area (called induration) across your forearm, not the red area around it. According to the Centers for Disease Control and Prevention, the size of this firm bump tells them if your test is positive or negative.

When The Test Gets Read

You must return to your healthcare provider 48 to 72 hours after getting the TB test for an official reading. Don’t try to read it yourself – trained professionals know exactly what to look for.

If you don’t come back within this time window, you’ll need to start over with a new test.

Understanding TB Test Results

What Different Measurements Mean

The size of any bump matters a lot. Here’s how doctors decide if your test is negative:

For Most Healthy People:

• Less than 15mm = negative result
• No special health risks
• Strong immune systems

For Higher-Risk People:

• Less than 10mm = negative result
• Recent contact with TB patients
• Healthcare workers
• People from countries with lots of TB

For Very High-Risk People:

• Less than 5mm = negative result
• Weak immune systems
• HIV-positive patients
• People taking immune-suppressing drugs

Why Your Risk Level Matters

Healthcare providers consider your medical history and TB risk factors to determine whether your test results are positive or negative. Two people with the same-sized bump might get different results based on their health situations.

What Negative Results Really Mean

The Good News

According to the CDC’s clinical guidance, a negative skin test result for TB infection means inactive TB or active TB disease is unlikely. This means:

• You probably haven’t been exposed to TB germs
• You’re not likely to get sick from TB right now
• You can’t spread TB to other people
• You probably don’t need TB treatment

When You Might Still Need More Testing

Your healthcare provider may do more tests, especially if you have TB symptoms like cough, weight loss, or tiredness, have HIV, or were recently exposed to TB germs.

Symptoms That Worry Doctors:

• Cough lasting more than 3 weeks
• Coughing up blood
• Chest pain
• Night sweats
• Unexplained weight loss
• Feeling very tired

When TB Tests Can Be Wrong

False Negative Results

Sometimes people have TB germs but get negative test results. The National Institutes of Health research shows that false-negative reactions can occur due to anergy (inability to react because of a weakened immune system), recent TB infection within the past 8 to 10 weeks, and many life-threatening illnesses.

Common Causes:

• Very new TB infection (less than 8 weeks ago)
• Weak immune system from illness or medicine
• Very severe TB disease
• Recent live virus vaccines
• Being too young (under 6 months old)
• Very old TB infections

False Positive Results

Some people may have a positive result even though they are not infected with TB bacteria, which can be caused by previous TB vaccination with the BCG vaccine or infection with other types of bacteria.

If you’ve had the BCG vaccine (common in other countries), your doctor might recommend a TB blood test instead.

What Happens After A Negative Test

Following Up With Your Doctor

Most people with negative TB tests don’t need treatment. However, your doctor might want to:

• Check your test results against your health history
• Order a chest X-ray if you have symptoms
• Schedule another test if you were recently exposed to TB
• Recommend blood testing for more accurate results

When You Need Repeat Testing

Some people need TB tests more than once:

Healthcare Workers:

• Often need yearly testing
• May need two-step testing when starting a new job
• Should get tested if exposed to TB patients

People With Risk Factors:

• Those living with TB patients
• People with weak immune systems
• Those traveling to high-TB countries

TB Blood Tests vs Skin Tests

When Blood Tests Work Better

According to the Cleveland Clinic, TB blood tests are the preferred test for people who have received the BCG vaccine, including children. Blood tests also work well for:

• People who can’t return for test reading
• Healthcare workers who need regular testing
• Anyone who had false results with skin tests

How Blood Tests Are Different

Blood tests measure how your immune system reacts to TB proteins in a lab. In most cases, you should get the results of your TB blood test within one to two days.

The biggest advantage? You only need one visit to the doctor’s office.

Taking Care Of Your Test Site

Right After The Test

Don’t cover the spot with a bandage or tape. Be careful not to rub it or scratch it. If the spot itches, put a cold cloth on it. You can wash your arm and dry it gently.

Do:

• Keep the area clean and dry
• Use a cold cloth for itching
• Wash gently with soap and water

Don’t:

• Scratch or rub the test spot
• Put bandages or tape over it
• Use creams or ointments

What’s Normal

It’s normal to have:

• A small bump right after the injection
• Slight soreness at the injection site
• The bump going away within a few hours

When To Worry About Your Results

Red Flags To Watch For

Call your healthcare provider right away if you notice:

• A bump that keeps growing after 72 hours
• Severe redness spreading from the test site
• Pus or drainage from the injection spot
• Severe pain or swelling
• Signs of infection like fever

Getting Peace Of Mind

Remember that a negative TB skin test usually means that you don’t have TB. If you’re worried about your results or have questions, don’t hesitate to contact your healthcare provider.

Most negative results are exactly what they seem – good news that you don’t have TB germs in your body.

Special Situations And Considerations

Children And TB Testing

TB testing in children works a bit differently:

• Very young children (under 6 months) might not react to tests yet
• Children need smaller bump measurements for positive results
• Doctors consider the child’s exposure history carefully
• Blood tests might be recommended for more accurate results

People With Health Conditions

If you have certain health problems, your doctor might interpret your results differently:

Conditions That Affect Test Results:

• HIV or AIDS
• Diabetes
• Kidney disease
• Cancer
• Organ transplants
• Taking steroids or other immune-suppressing drugs

Pregnancy And TB Testing

According to the Minnesota Department of Health, TB tests are safe during pregnancy. Most people can get a TB skin test, including pregnant women. However, doctors might prefer blood tests for pregnant patients who need quick results.

Getting Your TB Test Done

Where To Get Tested

You can get TB tests at:

• Primary care doctor offices like Yorktown Health
• Public health departments
• Urgent care centers
• Occupational health clinics
• Some pharmacies

What To Bring

When you go for your TB test, bring:

• Photo ID
• Insurance cards
• List of current medicines
• Information about any recent TB exposure
• Records of previous TB test results

Final Thoughts

A negative TB test is usually great news – it means you likely don’t have TB germs in your body and can’t spread TB to others. The test is “negative” if there is no bump or only a very small bump at the spot where the fluid was injected.

Remember that only trained healthcare providers should read your TB test results. Don’t try to interpret the results yourself, even if you think you know what they mean.

If you need a TB test or have questions about your results, contact the experienced team at Yorktown Health in Vernon Hills. We provide accurate testing and clear explanations to help you understand your health status. Our team makes sure you get the care and answers you need for peace of mind about your TB test results.