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Instant HIV Test

Window Period. 45 days after possible exposure

Sample(s) required. Blood from vein

Biological Marker. p24 HIV-1 antigen + combined HIV-1 and HIV-2 IgG/IgM

Accuracy. Specificity (number of true negatives): 100%
                  Sensitivity (number of true positives): 99%

Time for test results. 30 minutes

Cost of test. £130 (£70 with Drop and Go)

If you are worried about HIV and are looking for a rapid and accurate result, the 4th generation Instant HIV test may be a good option for you.

The 4th generation HIV test is typically conducted 45 days onwards after potential HIV exposure for a conclusive result.

If you are looking to get tested sooner, you can consider having the HIV-1 RNA PCR test which accurately detects the HIV-1 virus from 10 days onwards after potential exposure.

If you are concerned about a recent exposure (that happened less than 72 hours ago), it is essential to book in for a consultation, or contact the NHS, as soon as possible. You may be eligible for PEP (post-exposure prophylaxis) for HIV following an adequate assessment. However, you will need to have started PEP within 72 hours of exposure. After 72 hours, PEP will be ineffective.

If you are HIV-negative and concerned about how you can protect yourself from HIV, please book in for a consultation to discuss your options.

Same Day Appointments Available

Specialist & Friendly Professionals

Discreet & Confidential Service

The Process

If you want to skip the consultation and just have the test, you can try our Drop & Go service.


In order to be most prepared and leave plenty of time for questions & discussions, we will ask you to fill out a simple questionnaire.


We will begin by assessing your medical & sexual history, any symptoms you may be experiencing and discuss any questions you may have.

Sample collection

If it is still appropriate to proceed with the 4th gen HIV test (and you would like to), we will take a blood sample.

HIV management

If your results are positive, we can offer you support and advice on communicating your results to your partner(s) and accessing treatement.

We follow guidelines set by

Medicine is a complicated subject and sometimes these guidelines don’t always hold the answers.

For example, treating an STI in a patient who has developed a resistance to routinely used antibiotics.

Unlike most private clinics, we have medical consultants here to help you navigate through such problems and get you on the right track in no time.

Frequently Asked Questions

About The Test

How does the 4th generation HIV test work?

The 4th generation instant HIV test searches for the presence of HIV 1&2 antibodies and the p24 antigen within the blood.

After exposure to HIV, your immune system will begin to produce HIV antibodies as a response to the infection. This process is called seroconversion and occurs in the weeks following HIV exposure. The antibodies generated by the immune system are responsible for targeting the virus. These HIV antibodies persist throughout a patient's lifetime.

During the early stage of HIV infection, there is a high concentration of p24 antigen, which is a structural protein found in the HIV viral core. This antigen is detectable in the blood for a brief period before seroconversion takes place, after which it gradually decreases.

Due to its ability to test for the p24 antigen, the 4th generation HIV test is able to detect a HIV infection before the immune system begins to produce antibodies.

Is the 4th generation HIV test a serological test?

The term ‘serological’ refers to tests that analyse blood serum (the clear liquid portion of blood). The 4th generation HIV test is a serological test that detects both HIV 1&2 antibodies and p24 antigen, providing a comprehensive assessment of your HIV infection status.

What is the window period for the 4th generation HIV test?

If you are considering this test you should ideally wait for 45 days after exposure before being tested in order to confidently rule out HIV and remove the need for further testing.

After a HIV infection occurs, it typically takes about 2 to 4 weeks for the body to start producing detectable levels of the p24 antigen. During this time, the virus replicates rapidly, leading to an increase in the concentration of p24 antigen in the blood.

As the immune response progresses, the levels of p24 antigen begin to decline and eventually become undetectable, usually around 4 to 6 weeks after infection. It's important to note that the exact timing can vary from person to person, and some individuals may have detectable p24 antigen for a slightly longer or shorter period.

After the p24 antigen levels drop, it typically takes the body a few weeks to start producing detectable levels of HIV antibodies. The exact timing can vary from person to person, but on average, antibodies become detectable within 3 to 12 weeks after the initial infection.

However, the 4th generation Instant HIV test can detect HIV antibodies 45 days after exposure to the virus. This is because the majority of people with HIV have detectable levels of antibodies at this time.

Can taking PrEP or PEP affect the window period?

PrEP (Pre-exposure Prophylaxis) and PEP (Post-exposure Prophylaxis) medications are known to interfere with the performance and interpretation of the HIV antigen and antibody test results by altering the amount of virus in the blood, and potentially delaying the development of antibodies.

Furthermore, these medications will particularly affect the level of p24 antigen, causing it to either appear for a shorter period of time at a smaller level, or not appear at all.

If you are currently taking PrEP or PEP, you should take the 4th generation HIV test 45 days after completing your course of medications for a reliable and conclusive HIV result.

How accurate is the 4th generation HIV test?

The 4th generation Instant HIV test is a highly reliable test. The specificity (% of true negatives) is 100%, and the sensitivity (% of true positives) is 99%.

In the event that your 4th generation test is reactive, we will always confirm with a complimentary HIV-1 RNA PCR test and will send your sample to an external laboratory for confirmation.

How is the 4th generation HIV test different to the HIV-1 RNA PCR test?

The 4th generation HIV test and the HIV-1 RNA PCR test are both diagnostic tests used for detecting a HIV infection but they differ in their approach and the information they provide.

The 4th generation HIV test detects HIV 1&2 antibodies and the p24 antigen, a protein present in the HIV-1 virus. This test is commonly used as a screening test and can provide reliable results at 45 days and onwards after exposure.

On the other hand, the HIV-1 RNA PCR test detects the genetic material (RNA and proviral DNA) of the HIV-1 virus itself. This test measures the amount of HIV-1 RNA present in the blood. It is highly sensitive and can detect a HIV infection before antibodies are produced. The HIV-1 RNA PCR test can provide accurate and reliable results at 10 days after exposure.

You can read more about the HIV-1 RNA PCR test here.

Will I need an examination to have the 4th generation HIV test?

A physical examination is not routinely required for a 4th generation HIV test. However, if you are concerned about experiencing HIV symptoms, we can certainly offer you a examination during your consultation for your immediate reassurance.

How often should I take the 4th generation HIV test for regular screening?

We recommend testing every 3 to 12 months but this depends on your personal situation. You can discuss with your clinician regarding how frequently you should test if you have more than one sexual partner, change partners frequently, engage in chem-sex or any other risks that can increase your chance of getting HIV.

However, even if you are in a mutually monogamous relationship, you may seek reassurance with routine screening, especially if you are planning to conceive. Routine NHS antenatal tests include HIV testing.

How can I prepare for my 4th generation HIV test?

Here are a few tips on how to prepare for your appointment:

  • Drink enough water so that your veins are more prominent and easy to find.
  • Wear a loose fitting shirt or a short sleeved t-shirt so that the clinician can easily access your veins.
  • If you have any phobias of medical places or needles, please let our receptionists know at the time of booking your appointment.
  • Relax, Clarewell Clinics is a safe space. Your medical history with us is completely confidential so you can be as open and honest as you wish to be with us.

You will not need to make any extra precautions, and will be able to continue your day as normal.

Is my 4th generation HIV test confidential?

Yes. Everything you share with us is confidential and will not be shared with the NHS, your GP or anyone else unless you wish for us to do so.

About The Results

How long does the 4th generation HIV test result take?

The 4th generation HIV test results are available within 30 minutes. This allows enough time to cross check your results and repeat the tests if necessary.

A reactive result is always repeated, confirmed, and subjected to further testing before being shared with the patient.

How will I receive my 4th generation HIV test results?

You can receive your 4th generation HIV test results by either text or email.

What do my 4th generation HIV test results mean?

Your 4th generation HIV test results will either be reported as:

  • ‘NOT Detected’ (I.e. negative): You do not have HIV.
  • ‘Reactive’: Instant tests are designed to be highly specific (i.e. highly accurate when it comes to providing negative results). However, a reactive test result is always provisional and subject to further testing.
  • ‘Equivocal’: The test has been repeated twice but the results are invalid, thus requiring further testing.

If your results are reactive or equivocal, we will undertake a HIV RNA PCR test (at no additional cost) to check for the genetic material of the virus, and the results will be available within 4 hours.

Are my results conclusive if I test 45 days and onwards following my exposure?

Your results are conclusive at 45 days and onwards following your exposure. However, if you are on PrEP or PEP further testing will need to be repeated.

If you are currently taking PrEP or PEP, you should take the 4th generation HIV test 45 days after completing your course of medications for a reliable and conclusive HIV result.

Do I have to tell my partner if my 4th generation HIV test is reactive?

Your clinician will advise whether your reactive test result is provisional or has been confirmed as positive through further testing.

If a positive result has been confirmed, it is essential to inform all of your sexual partners so that they can get tested and treated appropriately. Your clinician will be able to advise and support you in this matter.

If you have had unprotected sex with a partner within the previous 72 hours, your partner should immediately visit a sexual health clinic or A&E in order to access PEP (post-exposure prophylaxis) for HIV. Please note that the eligibility for PEP is subject to the clinician’s discretion.

Can I get a certificate of my 4th generation HIV test results?

Yes, we provide a certificate of testing.

Please let us know at the time that you would like a certificate of testing and bring a proof of ID (passport or driving licence).


Sexual Health Consultation £60

4th Generation HIV Test (inc. consultation) £130

4th Generation HIV Test (with Drop & Go) £70

Health Insurance

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Next Steps 

In Clinic Care

Same Day Testing Available

Online Care

Same Day Telephone / Video Consultation

Reviewed by: Dr Manoj Malu
Written By: Shannon Abraham

Last reviewed date: 13 October 2023
Next review due: 13 October 2026

Whilst this content is written and reviewed by sexual health specialists, it is for general guidance only. It is not intended to replace the advice of your clinician.