Can a Brain Scan, Blood Test or Computer Test Diagnose ADHD?

But ADHD isn't diagnosed that way. This guide explains why blood tests and brain scans can't confirm ADHD, what computer tests like the QbTest can and can't do, and how ADHD is actually diagnosed.

ADHD is a neurodevelopmental condition. It affects how the brain manages attention, activity and impulses. But it doesn't leave a single, clear marker that a test can pick up.

Instead, ADHD is recognised by a pattern of experiences over time. To be diagnosed, ADHD traits need to:

• have started in childhood
• show up in more than one setting, such as home, school or work
• have lasted over time
• have a real impact on daily life

No scan or blood sample can show these things. They can only be understood by looking carefully at someone's life, from childhood to now.

No. There is currently no blood test for ADHD.

Sometimes a GP or specialist may suggest blood tests, but this is to rule out other causes of similar difficulties, such as:

• thyroid problems
• low iron or anaemia
• vitamin deficiencies

These can affect energy, focus and mood. Checking for them makes sure nothing else is being missed. Blood tests may also be used before starting some ADHD medications, to check that treatment is safe. But a normal or abnormal result can't tell you whether someone has ADHD.

No. Research has found some differences in brain structure and activity between groups of people with and without ADHD. But these differences are small, they vary a lot between individuals, and they overlap with people who don't have ADHD.

This means a scan can't show whether one particular person has ADHD. NICE guidelines say brain imaging should not be used to diagnose ADHD.

You may come across private clinics offering brain scans, such as SPECT or EEG, as a way to diagnose ADHD. These aren't recommended in the UK, and they can be expensive. If a brain scan is ever suggested, it's usually to look into a different medical concern, not to confirm ADHD.

Computer tests, sometimes called continuous performance tests, measure how someone responds to a simple task on a screen over a set period of time.

The best known in the UK is the QbTest. It usually takes around 15 to 20 minutes. The person responds to shapes on a screen, while a camera tracks small movements of their head. It measures:

• attention, such as how consistently someone responds
• impulsivity, such as how often they respond when they shouldn't
• activity, such as how much they move while doing the task

The results are compared with other people of the same age and gender.

In 2024, NICE recommended that the QbTest can be used to help assess ADHD in children and young people aged 6 to 17. The key word is "help". It should only be used alongside a full clinical assessment, never instead of one.

Computer tests can be useful because they:

• add objective information to the wider picture
• can help clinicians reach a decision more quickly in some cases
• give families something concrete to discuss

But they also have important limitations:

• They only show a short snapshot. A 20-minute task can't capture how someone manages over weeks, months or years.
• They happen in one setting. ADHD needs to show up across different areas of life, not just during a test.
• Other things can affect results. Tiredness, anxiety, low mood, sleep problems or simply being in a new situation can all change how someone performs.
• Some people perform well under test conditions. A new, structured task can help people with ADHD focus for a short time, so a "normal" result doesn't rule ADHD out.
• They can't look back. A computer test can't show whether difficulties began in childhood.

That's why a computer test result is always one piece of evidence among many, and is never the deciding factor on its own.

ADHD is diagnosed through a detailed assessment with a specialist clinician, following DSM-5 or ICD-11 criteria and NICE guidelines. This usually includes:

• questionnaires about ADHD traits and how they affect daily life
• information from others, such as parents, teachers or a partner
• a clinical interview, such as the DIVA-5 for adults, exploring childhood and the present day
• a look at physical and mental health, to consider other explanations

It may not feel as straightforward as a scan or a blood test. But a careful conversation about someone's whole life is the most reliable way to understand whether ADHD is the right explanation, and what support will help.

Raiys works nationwide, offering online ADHD assessments for adults and for children and young people aged 5 to 17 across the UK. Our experienced, specialist ADHD team follows NICE guidelines, bringing together questionnaires, information from people who know you or your child, and a detailed clinical interview. You'll receive a detailed written report, usually within 14 days.

If you're in crisis right now, call 999, go to A&E, or call Samaritans free on 116 123, any time of day or night.

Ready to take the next step? Find out more about our adult ADHD assessment or child ADHD assessment.

There's no shortcut to an ADHD diagnosis. But a thorough assessment means you can trust the outcome, whatever it is.