Key takeaways
- Platelets are the blood cells that help your blood clot, and your count is measured as part of a full blood count.
- At Blood London, a full blood count costs £63.75 plus the £50 blood draw, with results back in 1 day.
- A mildly high or low platelet count is common and usually has a benign, temporary cause.
- Clumping of platelets in the sample tube is a frequent, harmless cause of a falsely low reading, which a repeat test can rule out.
- Very low platelet counts, or bleeding symptoms such as unusual bruising or bleeding gums, need same-day medical advice.
- Platelet results are read alongside the rest of the full blood count and your symptoms, not in isolation.
Platelets are small blood cells that clump together to stop bleeding and start the clotting process. A platelet count outside the expected range is common and usually reflects something temporary, such as a recent infection, but a very low count or bleeding symptoms need same-day advice. Platelets are measured in the full blood count at Blood London.
Book a full blood count at 117a Harley Street: £63.75 plus the £50 blood draw, results in 1 day.
What do platelets actually do?
Platelets circulate in your blood and clump together at the site of an injury to form the first stage of a clot, working alongside clotting proteins to stop bleeding. They are made in the bone marrow and normally survive in the bloodstream for around a week before being replaced. Because platelets are counted as part of a full blood count, a platelet result almost always arrives alongside your red cell and white cell counts, which helps put it in context. Our guide to full blood count results explains the other lines on the report.
What commonly causes a high platelet count?
A mildly high platelet count is common and most often reflects the body's response to something else, such as inflammation, iron deficiency, or recovery from a recent infection, rather than a problem with the platelets themselves. This pattern, sometimes called a reactive rise, usually settles once the underlying cause resolves. Persistently high counts without an obvious cause are less common and are the kind of result a doctor would want to look into further, alongside your history and the rest of your blood count. In adults over 40, NICE lists a raised platelet count as one of the findings that can prompt a doctor to consider further tests, particularly alongside other symptoms.
What commonly causes a low platelet count?
A low platelet count often follows a recent viral illness or certain medicines, and in many people it settles on its own without treatment. Heavy drinking, liver disease and pregnancy can also lower the count. One of the most frequent causes of an apparently low reading is not a true drop in platelets at all, but clumping of platelets in the sample tube during processing, which a repeat test using a different collection method can usually rule out. Less commonly, a persistently low count can reflect how the bone marrow is working, or an immune condition, which is why an unexplained or persistent low result is followed up rather than dismissed.
The table below summarises common patterns and what they usually mean.
| Pattern | How common | Usual cause | What tends to happen next |
|---|---|---|---|
| Mildly high, isolated | Common | Inflammation, iron deficiency, recent infection | Often settles; reviewed alongside the rest of the count |
| Mildly low, isolated | Common | Recent viral illness, certain medicines, sample clumping | Repeat test to confirm the true count |
| Persistently high | Less common | Needs further assessment | Doctor review and further tests |
| Persistently low, or with bleeding symptoms | Less common | Needs further assessment, may need same-day care | Same-day medical advice if bleeding symptoms are present |
When does a platelet result need same-day medical attention?
A platelet result needs same-day medical attention when it is very low, or when it comes with bleeding symptoms such as unusual or widespread bruising, blood in your urine or stools, bleeding gums, nosebleeds that will not stop, unusually heavy periods, or a rash of tiny red or purple spots that do not fade when pressed. These symptoms alongside an abnormal count should be assessed by a doctor the same day, and severe bleeding is a reason to go to A&E or call 999. A rash that does not fade under a glass, together with a fever or feeling very unwell, is an emergency: call 999.
Why might my platelet count be repeated before anything else is done?
A platelet count is often repeated before further action is taken, because clumping in the original sample is a common and harmless cause of a falsely low reading, and a single mildly abnormal result outside the laboratory's reference range can occur by chance in a healthy person. A repeat test, sometimes using a different tube or method, confirms whether the result reflects your true platelet count before a doctor considers what, if anything, caused it.
How testing works at Blood London
Platelets are measured as part of a full blood count, which costs £63.75 plus the £50 blood draw, with results usually back within 1 day. The Haematology Profile pairs the full blood count with ESR, a general inflammation marker, for £75 plus the £50 blood draw, also with results in 1 day. No fasting is needed. As with all our private blood tests in London, you can walk in or book online at 117a Harley Street, seven days a week, with no GP referral needed, and your results are sent to you by email showing each result against the laboratory's reference range. You can add a doctor review of your report to your test for £75.
Book a full blood count at 117a Harley Street: £63.75 plus the £50 blood draw, results in 1 day. Start your booking.
Frequently asked questions
Is a high platelet count a sign of cancer?
Usually not. A high platelet count is far more often a reactive response to inflammation, iron deficiency or infection. In adults over 40, though, a persistently raised count without an obvious cause is one of the findings NICE asks doctors to consider alongside other symptoms, so it should be reviewed by a doctor.
Can dehydration affect my platelet count?
Dehydration can concentrate your blood generally, which sometimes affects how counts appear, but it is not a typical cause of a genuinely high or low platelet result on its own.
Why was my platelet count different on a repeat test?
Sample handling, including how quickly it was processed and whether platelets clumped in the tube, can affect a single reading. A repeat test in different conditions often gives a more reliable count.
Do certain medicines lower platelet counts?
Yes, some medicines can lower platelet counts as a side effect. Mention any medicines you are taking to the phlebotomist or your doctor if your count is unexpectedly low.
Should I avoid exercise if my platelet count is low?
If you have a confirmed low platelet count, ask a doctor for advice on activity, since very low counts can increase bleeding risk with injury. This is a question for your doctor rather than a general rule.
How is a platelet problem actually diagnosed?
A single count is rarely enough. A doctor looks at a repeat test, the rest of your full blood count, your symptoms and sometimes a blood film examined under a microscope before reaching a conclusion.
References
- NHS: Blood tests
- Lab Tests Online UK: Platelet count
- NHS: Immune thrombocytopenia (ITP)
- NICE guideline NG12: Suspected cancer, recognition and referral