Latent TB test
A blood test or skin test that checks whether you carry tuberculosis bacteria quietly, without being unwell or infectious, so it can be treated before it ever causes illness.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- Latent TB means TB bacteria are present but dormant: you feel well, have no symptoms and are not infectious.
- The test (an IGRA blood test or a Mantoux skin test) only shows the bacteria are there — it cannot tell latent from active TB by itself.
- Treating latent TB now greatly lowers the chance of it becoming active disease later, especially if your immune system weakens.
- A positive result means you should be checked for active TB before any preventive treatment, and free NHS pathways exist for those at risk.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your specialist will give you advice for your situation.
Identifies hidden TB infection before it can cause illness
A latent TB test is the wrong test if you have symptoms suggesting active TB; that needs assessment for active disease (sputum tests, imaging) instead.
You can carry on as normal. After a blood test you may have a small bruise; after a skin test, avoid scratching the spot and return when asked.
A clear explanation of what the result means and what it does not.
You can carry on as normal. After a blood test you may have a small bruise; after a skin test, avoid scratching...
You return so the clinician can measure the raised area at the injection site and tell you whether it is positive.
The laboratory result comes back and is explained to you, including whether any further test is needed.
You are assessed for active TB, usually with questions, an examination and a chest X-ray, before any preventive...
What is a latent TB test?
Tuberculosis (TB) is an infection caused by bacteria. Many people who breathe the bacteria in do not become ill: their immune system contains it, and it sits quietly in the body. This is called latent TB infection. You have no symptoms, you feel well, and you cannot pass it to anyone.
A latent TB test checks whether your immune system has met these bacteria. There are two kinds: a blood test called an IGRA (interferon-gamma release assay) and a skin test called the Mantoux test. Neither tells you that you are ill — they only show whether the bacteria are present in a dormant form.
The point of testing is prevention. Latent TB can 'wake up' and become active TB disease later, especially if your immune system is weakened. Finding and treating it now greatly reduces that risk.
A latent TB test cannot, on its own, tell active TB apart from latent TB. If a test is positive, the next step is to check you do not have active TB before any treatment for latent infection is offered.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
Blood test vs skin test
| Feature | IGRA (blood) | Mantoux (skin) |
|---|---|---|
| Visits | Usually one | Two (inject, then read) |
| Affected by BCG? | No | Can be affected by BCG history |
| Result timing | Within days | Read at 2–3 days |
| Tells active from latent? | No | No |
Neither test distinguishes latent from active TB. A positive result always needs an assessment for active disease.
Preparing for your test
- There is no need to fast or stop your usual medicines before either test.
- Tell the clinician if your immune system is weakened (for example by HIV, certain medicines, or before starting a biologic drug), as this affects which test is used and how results are read.
- Mention any past TB, TB contact, or whether you have had the BCG vaccination.
- Say if you have had a recent live vaccine (such as MMR), as this can affect the timing of a skin test.
- For a skin test, plan to return in 2 to 3 days to have it read, and avoid scratching or covering the spot tightly.
- Bring details of any recent travel or where you have lived, as this helps assess your risk.
- Ask whether you are being tested because of contact with someone with TB, or as part of routine screening.
What happens
For the IGRA blood test, a healthcare worker takes a small blood sample from your arm. It is sent to a laboratory and you are told the result, usually within a few days.
For the Mantoux skin test, a tiny amount of fluid is injected just under the skin of your forearm, raising a small bleb. You go home and return after 2 to 3 days so the clinician can measure the firm raised area (not just the redness) at the site.
If either test is positive, it does not by itself mean you have active TB. The next step is an assessment — questions about symptoms, an examination and usually a chest X-ray — to check you do not have active disease before any treatment for latent infection is discussed.
If the test is negative, you will be told whether any repeat or further testing is needed based on your circumstances.
Is this test right for me?
A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.
May not be suitable if…
- A latent TB test is the wrong test if you have symptoms suggesting active TB; that needs assessment for active disease (sputum tests, imaging) instead.
- A negative test should not be relied on to exclude TB in someone with a very weakened immune system.
- Routine testing of low-risk people without exposure or an immune-suppression reason is not generally recommended.
- It cannot, by itself, decide whether you need treatment; that depends on excluding active TB and weighing your individual risk.
Delay or rearrange if…
- You may have active TB symptoms and need urgent assessment first.
- You have had a recent live vaccine, which can affect a skin test (your clinician will advise on timing).
- A previous indeterminate result needs repeating under the right conditions.
- You cannot return to have a skin test read within the required window.
Alternatives to discuss
- The other test type (blood instead of skin, or vice versa) where one is unsuitable
- Both tests together for people with a severely weakened immune system
- Assessment for active TB if symptoms are present, rather than a latent test
- Watchful monitoring with advice on symptoms if testing is not indicated
- No test if your risk is low and there is no exposure or immune-suppression reason
Before you decide
Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Benefits
- Identifies hidden TB infection before it can cause illness
- Allows preventive treatment that greatly reduces the chance of active TB later
- Helps protect people around you in the longer term, since treated latent TB cannot progress and spread
- Important before starting treatments that weaken the immune system, such as some biologics
- The blood test usually needs only one visit and is not affected by past BCG
- Available free on the NHS for those at higher risk
Risks & complications
- Brief discomfort, a small bruise or a raised bleb at the test site
- For the skin test, needing a second visit to have it read
- Mild itching or redness at a skin-test site
- An unclear or 'indeterminate' blood-test result that needs repeating
- A result that does not fit the clinical picture, needing the other test or specialist review
- Anxiety while waiting, especially if you have been in contact with someone with TB
- A false negative if the immune system is very weak, which is why both tests are sometimes used together
- A larger local skin reaction to the Mantoux test
- Feeling faint when blood is taken
The most important limitation is that these tests cannot tell latent TB from active TB, and a negative test does not completely rule TB out, especially if your immune system is weakened. If you have symptoms such as a long-lasting cough, fevers, night sweats or weight loss, you need assessment for active TB regardless of a latent-test result. Ask your clinician what your result changes and what the next step is.
Published figures to discuss
These tests are useful but imperfect. Neither distinguishes latent from active TB, both can occasionally be falsely negative when the immune system is weak, and the Mantoux test can be influenced by past BCG. Reported sensitivity and specificity vary widely between populations and laboratories, so we have not quoted precise figures here; the result should always be read alongside your symptoms, history and risk rather than as a stand-alone number.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Positive IGRA or Mantoux does not distinguish latent from active TB | Core limitation | Symptoms, chest X-ray and clinical assessment are needed before deciding this is latent TB. | Guide sourcesClinical context |
| False negative test | Higher with immunosuppression, very recent exposure or young age | A negative test does not always exclude infection in high-risk contacts or immunocompromised patients. | NICE NG33 — Tuberculosis: recommendationsnice.org.ukSource-linked context |
| Starting latent TB treatment before excluding active TB | Unsafe | CDC/NICE-style guidance is clear that active TB must be excluded first to avoid undertreatment and resistance. | NICE NG33 — Tuberculosis: recommendationsnice.org.ukSource-linked context |
| Liver toxicity from preventive treatment | Drug- and patient-dependent | Isoniazid and rifamycin regimens need side-effect counselling and monitoring in higher-risk patients. | NICE NG33 — Tuberculosis: recommendationsnice.org.ukSource-linked context |
These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.
What happens afterwards
There is no physical recovery from a latent TB test. 'Afterwards' is about getting your result, being checked for active TB if it is positive, and deciding whether preventive treatment is right for you.
- A small bruise after a blood test, or a raised, slightly itchy spot after a skin test
- No change in how you feel, because latent TB causes no symptoms
- Being asked to return to have a skin test read
- Being referred for a chest X-ray if the test is positive
Aftercare
- Return on time to have a skin test read; an unread test has to be repeated.
- Keep a note of your result and what you were advised to do next.
- If your test is positive, attend the assessment for active TB that follows.
- Tell any clinician planning to start you on immune-weakening treatment about your TB result.
- Watch for symptoms of active TB (persistent cough, fever, night sweats, weight loss) and seek advice if they appear.
- If preventive treatment is offered, discuss the benefits, the course length and any side effects before deciding.
- Ask whether household members or close contacts should also be tested.
- A return appointment booked for a skin-test reading, if relevant
- A note of your result and the next step
- Details of any TB contact or travel to share with the clinic
- An up-to-date list of your medicines, especially any biologics planned
- Awareness of active-TB symptoms to watch for
- Questions ready about whether preventive treatment is right for you
⚠ Get urgent help if…
- A cough lasting more than three weeks, especially with phlegm or blood — this needs assessment for active TB.
- Unexplained fevers, drenching night sweats or weight loss.
- Feeling increasingly unwell, very tired or breathless.
- A large, blistering or ulcerating reaction at a skin-test site.
- Symptoms of active TB if you are about to start, or are taking, an immune-weakening medicine — seek advice promptly.
Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.
General guidance — it doesn't replace the specific advice your specialist gives you.
Results & realistic expectations
A positive test means TB bacteria are present in your body, but it does not say whether the infection is latent (dormant) or active (causing disease). That is why a positive result is followed by an assessment for active TB, usually including a chest X-ray, before any decision about treatment.
A negative test makes TB infection less likely but does not completely exclude it, particularly if your immune system is weakened or the test was done very soon after exposure. Your clinician interprets the result alongside your symptoms, history and risk, not in isolation.
A latent TB test reflects your situation at the time it is taken. A negative result can change if you are later exposed to TB, so repeat testing may be advised after a new contact or before immune-weakening treatment. A positive result does not need repeating to confirm infection, but the decision about preventive treatment may be revisited if your circumstances change.
Related tests, treatments or support
Latent TB testing is often arranged alongside HIV testing, because HIV affects the immune system and the two influence each other. It is also commonly done before starting biologic medicines for conditions such as inflammatory arthritis or bowel disease, and as part of new-entrant or contact screening. Your clinician may test for hepatitis B and C at the same time in some settings.
Follow-up & long-term care
If your test is negative and you have no symptoms, you may need no further action, or a repeat at a later date depending on your risk. If it is positive, you are referred for assessment to exclude active TB, and then for a discussion about preventive treatment. TB services follow up people on treatment for latent infection to check progress and manage any side effects.
- Repeat testing may be advised after a new TB contact or before immune-weakening treatment.
- If you start preventive treatment, attend reviews to monitor for side effects and progress.
- Stay alert to active-TB symptoms even after a negative test, especially if your immune system is weakened.
- Keep a record of your result to share with future clinicians.
Repeat, follow-on and what comes next
- Indeterminate blood-test results sometimes need repeating.
- A negative test may be repeated after a new TB contact or before immune-weakening treatment.
- A positive test is followed by further assessment (including a chest X-ray) rather than repeated to confirm.
- Sometimes the other test type is added when the first does not give a clear answer.
Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.
What good aftercare looks like
- A clear explanation of what the result means and what it does not.
- A defined pathway to assess for active TB if the result is positive.
- A balanced discussion of preventive treatment, including course length and side effects.
- Monitoring and a named contact for anyone who starts treatment for latent infection.
- Advice on active-TB symptoms to watch for, even after a negative test.
What affects the cost
Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:
- Which test is used (IGRA blood test or Mantoux skin test)
- Whether a second visit is needed to read a skin test
- Laboratory processing for the blood test
- Any follow-up assessment and chest X-ray if the result is positive
- A consultation to interpret the result and discuss treatment
- Whether testing is bundled with HIV or hepatitis testing or pre-biologic screening
- Which test is included (blood, skin, or both)
- Whether the skin-test reading visit is included
- How and when you will receive the result
- Whether follow-up for a positive result (assessment and chest X-ray) is included or referred on
- Whether a consultation to interpret the result is included
- What happens if the result is indeterminate and needs repeating
On the NHS? Latent TB testing is offered free on the NHS for people at higher risk, such as close contacts of someone with TB, some new entrants from high-incidence countries, and people about to start immune-weakening treatment; private testing is mainly used for speed or occupational requirements.
You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.
Consent traps and marketing red flags
These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.
Consent traps
- Being told a positive result means active TB, without the follow-up assessment being explained.
- Relying on a negative result to rule out TB in someone immunosuppressed.
- Not explaining that latent TB is symptom-free and not infectious.
- Starting preventive treatment without weighing individual benefits and side effects.
- Not arranging the second visit needed to read a skin test.
Marketing red flags
- Selling a TB blood test as a way to 'rule out TB' regardless of symptoms.
- Offering testing without any plan for following up a positive result.
- Implying a single test can diagnose active TB.
- Encouraging routine testing of low-risk people with no exposure or immune-suppression reason.
Choosing a specialist safely
- Check the specialist is on the GMC Specialist Register for this area.
- Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
- You're entitled to time to consider and to have your questions answered before you agree — the specialist who looks after you should explain it, not a salesperson.
- Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
- You're entitled to your total cost in writing — including any follow-up — before you decide.
Questions to ask your medical professional
Take this to your consultation. A good specialist will welcome every one of these.
- Am I being tested because of a known TB contact, or as routine screening?
- Will I have the blood test, the skin test, or both, and why?
- If my result is positive, what happens next to check for active TB?
- What would preventive treatment involve, and what are its benefits and side effects for me?
- Could my immune system affect how reliable the test is?
- Should my household or close contacts also be tested?
- Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
- Will you be the specialist who carries out my test, and who looks after me afterwards?
- What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
- What does a realistic result look like — and what can this test not achieve?
- What are my options, including waiting, doing nothing for now, or choosing a different approach?
- Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
- What is the total cost in writing, including any follow-ups, and how much time do I have to decide?
Frequently asked questions
Does a positive test mean I have TB disease?
Am I infectious if I have latent TB?
Will the BCG vaccine affect my result?
Is the test available on the NHS?
Do I have to be treated if my test is positive?
Which test will I have, blood or skin?
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How we made this page
Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →
Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.
Sources & standards: NICE NG33 — Tuberculosis: recommendations NICE QS141 — Latent TB testing for people from high-incidence countries NHS — Tuberculosis (TB): diagnosis NHS — Tuberculosis (TB) UKHSA — Tuberculosis: guidance, data and analysis
Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.
Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.
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