INTERVAL Main Results

Main Results

What do the findings of the study show?

The study showed that, over 2 years, the majority of donors could give blood more frequently without having a major impact on their health. Information on how different people can give blood safely could boost the supply of blood to the NHS. More details on the study’s findings is found here.

Will I now be able to donate more often?

No, not at the moment. The new research may change the official recommendations on donation. For now, the intervals between blood donations will stay the same (every 12 weeks for men and every 16 weeks for women).

It will take some time to translate the findings of the INTERVAL study into routine donation practice. In particular, NHS Blood and Transplant will need to understand which type of donors can safely donate more often without an adverse impact on their iron stores.

If there are changes to recommendations on donation frequency, will I have to donate more often?

No, you can decide to donate at a frequency that suits you.

I was told I had low haemoglobin/iron levels during the study, how often should I be donating?

NHSBT’s routine health screening procedures assess whether your haemoglobin levels are safe for you to donate. If you do not pass these tests then you will be deferred for a given period of time.

The study shows that while some donors could donate more frequently than the current donation intervals, other donors should donate at longer intervals. These findings will allow greater personalisation of blood donation. In the future, some donors may give blood more often, and some less depending on specific characteristics.

Will you be able to tell me the results from measurement in my blood samples?

During the 2-year INTERVAL study, we collected research samples when you joined and at your 2-year anniversary. We measured fresh blood samples and froze some of your blood for future tests. We measured your full blood count and if any results could have an immediate impact on your healthcare (such as a low haemoglobin level or high platelet count), we will have told you.

It is not planned to feedback any further results as these are research results and not designed for clinical tests.

Will there be any other changes to the donation service based on the study’s results?

The results from the trial suggest that we need better screening methods to measure haemoglobin levels in potential donors. A further study (COMPARE) is now looking at how different tests can spot donors who meet or fall below the haemoglobin threshold for donation ( This study, in almost 30,000 donors, is now completed and we are looking at the results. NHS Blood and Transplant will use the results to decide on the best screening method in the future.

Have there been other publications from INTERVAL and where can I find them?

Yes, publications are found at Publications include those relating to:

i) Analysis of INTERVAL data and samples to answer the trial’s main questions about optimum donation intervals
ii) Results of other studies that INTERVAL participants have been involved in
iii) Findings of research involving the use of samples and data collected during the INTERVAL trial looking at donor and public health-related questions.

Will there be further publications about the INTERVAL study?

Yes. There will be many more publications relating to the INTERVAL trial including the results of:

  1. INTERVAL Phase II where some donors gave blood at their study-allocated donation frequency for a period of up to 4 years
  2. INTERVAL Phase III in which some donors provided a series of research samples across 2 or more donations
  3. Research looking at whether increasing donation frequency is a cost-effective way of increasing the supply of blood.
Will I be asked to be involved anything further for the INTERVAL study?

The INTERVAL research team or NHS Blood and Transplant may ask if you would like to help with other studies to help with blood donation or other important public health questions. You can decide if you want to help or not. Your decision will not affect your blood donation now or in the future. Other research which INTERVAL participants have been involved in after the INTERVAL trial include:

  • NIHR BioResource: This is funded by the Department of Health to help understand what causes important conditions such as cardiovascular disease and diabetes. The BioResource recruits healthy volunteers and participants who agree to be invited in the future to participate in ethics-approved research studies. Over 12,000 INTERVAL participants have joined NIHR BioResource.
  • INFORM: A subset of INTERVAL participants was invited to the University of Cambridge-led INFORM study. We considered if providing people with different types of information about their individual risk of a heart attack would help them change their lifestyle (for example to eat a healthier diet, exercise more or stop smoking). Publications relating to the INFORM trial can be found here.
  • CARRIAGE: Small numbers of INTERVAL participants were asked to help with a study of bacteria carried in the nose. Donors took nasal swabs to help researchers identify who did and didn’t carry the bacterium Staphylococcus aureus (S. aureus). This is important, as carriers are at much greater risk of all types of S. aureus infections. Further information about the study can be found here.
If donors wish to discuss the finding of the research with someone who should they contact?

Please send an email to letting them know the nature of your query and they will refer it to the relevant person to provide you with a response.