Is there a test for dementia? This is what your GP does

There is no single test that proves dementia. No blood test, no home test, and no scan that settles it on its own. What does exist is a sequence of steps your GP works through, in which blood work plays a clear but modest part.

That is less satisfying than a simple yes or no. It is also the truth.

What is a memory test exactly?

A memory test is a short set of questions and tasks: remember a few words, draw a clock, count backwards. Your GP uses it to see whether something more than ordinary forgetfulness is going on. Such a test gives an indication, not a diagnosis.

You cannot pass or fail it. It exists to show whether further investigation is needed.

Which steps does your GP work through?

Usually four. First a conversation with you, and often with your partner or child, because they sometimes notice changes earlier. Then a memory test. Then blood work, to rule out treatable causes. And only if the picture stays unclear, a referral to a memory clinic.

So the diagnosis comes from the sum, not from any single result.

Then why does the GP request blood work?

To see whether something treatable is contributing. A vitamin B12 deficiency, an underactive thyroid, anaemia, disturbed blood sugar or an upset salt balance can all slow your thinking. These causes are not often the explanation, but you do not want to miss them (Muangpaisan et al., 2012).

With the thyroid, the nuance matters. The link between a mildly underactive thyroid and cognitive complaints is contested, and not every study finds it (Wilson et al., 2022).

I point that out deliberately. There is far too much certainty in how people talk about what blood can explain, and it helps nobody.

Which values sit on the list is set out in tired and forgetful.

Can a blood test detect dementia?

No. A standard blood test cannot detect dementia, cannot rule it out and cannot predict it. New blood markers for Alzheimer's are being researched, but in the Netherlands they are not part of ordinary GP care. What blood can do is bring treatable causes into view.

So do not buy a home test that promises to find dementia. Nobody can deliver on that promise.

What a blood test does usefully show, and which two risk factors are visible in it, is covered in preventing dementia.

An example from practice

An example helps here. Picture a man of 72 who visits his GP with his daughter. He scores moderately on the memory test. His blood shows a TSH of 9.8 mIU/l, pointing to an underactive thyroid, and a vitamin B12 of 145 pmol/l.

Those two values do not make the diagnosis. They do change the order of what happens next.

Both are treated first, and the picture is reviewed again a few months later. If nothing has changed by then, the referral follows after all. That is how you avoid a treatable cause being written off as dementia.

When does the GP refer you on?

When the picture stays unclear, when you are younger than 65, or when symptoms worsen quickly. The memory clinic then runs more extensive tests, often including a scan and a longer battery of assessments. The same rule holds there: the diagnosis comes from the whole picture.

The Hersenstichting and the RIVM describe the same route. They also stress that no single test handles this on its own.

In my view that is the reassuring part. No single number decides this, and no single number can be wrong about you on its own.

If you mostly notice forgetfulness without other complaints, read when forgetfulness is normal first. If you want the treatable causes checked now, a complete blood count covers part of that ground. The fourteen risk factors from the Lancet report sit apart from this (Livingston et al., 2024).

References

1. Muangpaisan W, et al. (2012). Prevalence of potentially reversible conditions in dementia and mild cognitive impairment in a geriatric clinic. Geriatr Gerontol Int. PMID 21794050.
2. Wilson S, et al. (2022). Subclinical Hypothyroidism and Cognitive Impairment. J Alzheimers Dis. PMID 35694927.
3. Livingston G, et al. (2024). Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission. The Lancet. PMID 39096926.
4. Hersenstichting. Diagnosing dementia: how does it work? hersenstichting.nl.
5. RIVM. Figures on dementia in the Netherlands. rivm.nl.

Would you like the treatable causes of memory complaints checked at a calm moment, without first booking an appointment with your GP? At Levenswijs Health you can. Every result is reviewed by a doctor registered in the Dutch BIG register. A blood test does not provide a diagnosis and cannot detect dementia. For treatment decisions, always discuss your results with your GP.