Platelets are tiny cells in the blood that help bleeding stop; the normal count in adults is 150,000 to 450,000 per microlitre [1]. A low platelet count usually has a simple cause, such as platelets clumping together in the test tube, a viral infection, a medicine, liver disease or pregnancy; it is also common during chemotherapy and usually comes back up a few weeks after each cycle [1, 2, 5]. A high platelet count is also usually caused by tissue damage (such as surgery), infection, inflammation or iron deficiency [7, 8]; but if it is still high on a second test in an adult aged 40 or over, the cause, including cancer, should be looked for [9].
Key points
- The normal platelet count is 150,000 to 450,000. As long as the count is above 50,000, most people have no symptoms [1].
- Check a low count without symptoms by repeating the test first; sometimes platelets have only clumped together in the test tube and the count is wrongly reported as low [1].
- During chemotherapy, platelets are checked before every cycle, and the level needed depends on the drug: for example, the next cycle of carboplatin is given once the count is at least 100,000, and of oxaliplatin once it is at least 75,000 [5, 6].
- A platelet count below 10,000, or bleeding that will not stop, is an emergency [1, 2].
- Most high platelet counts are the body's reaction to another problem, not cancer [7]; but a high count that stays high on a repeat test in an adult aged 40 or over is worth investigating [9].
Low platelet count: what causes it?
A platelet count below 150,000 is called a "low platelet count" (thrombocytopenia): 100,000 to 150,000 is mild, 50,000 to 100,000 moderate and below 50,000 severe [1]. Platelets fall for three main reasons: the bone marrow makes fewer platelets, platelets are destroyed faster in the blood, or an enlarged spleen holds on to them [1].
The first step is to make sure the number is right. Sometimes platelets clump together only in the test tube and the machine counts fewer than there really are. Repeating the test in a different tube and counting the platelets under a microscope makes this clear [1].
| Cause | Explanation | What to do |
|---|---|---|
| Platelets clumping in the test tube (false low count) | The platelet count in the body is normal and causes no bleeding [1] | Repeat the test in a different tube [1] |
| Viral and some other infections | Such as Epstein-Barr virus, hepatitis C, HIV, COVID-19, chickenpox, measles, mumps, dengue, malaria and the stomach bacterium Helicobacter pylori; these infections usually slow down the bone marrow [1] | Treat the infection and repeat the test as your doctor advises [1] |
| Medicines | Such as the blood thinner heparin, some antibiotics (vancomycin, linezolid, co-trimoxazole and penicillins), the tuberculosis medicine rifampicin and some epilepsy medicines [1] | Tell your doctor about all your medicines and do not stop any of them on your own |
| Heavy drinking and chronic liver disease (such as cirrhosis) | The liver makes less of the hormone that produces platelets, and an enlarged spleen holds on to platelets; 6 to 8 in 10 people with chronic liver disease have a low platelet count [1] | Liver check-up and stopping alcohol [1, 2] |
| Pregnancy | Platelets fall in 5 to 10 in every 100 pregnancies; most of these are a mild type specific to pregnancy that goes away after birth and does not harm the baby [1] | Follow-up with your obstetrician [1] |
| Lack of vitamin B12 or folic acid | The bone marrow makes fewer blood cells [1] | Testing and treating the deficiency |
| Autoimmune platelet disease (ITP) | The immune system destroys the body's own platelets; the other blood cells are normal and the platelet count is usually below 100,000 [1] | See a haematologist; treatment depends on the platelet count and on bleeding [3] |
| Chemotherapy and some targeted therapies | They lower the platelet count [2] | See the section "Low platelets during chemotherapy" |
| Bone marrow diseases | Such as leukaemia, lymphoma or a cancer that has spread to the bone marrow, and myelodysplastic syndrome (a disease in which the bone marrow does not make blood cells properly) [1] | A low platelet count together with anaemia or an abnormal white cell count needs urgent assessment [1] |
This table does not replace an examination by a doctor. For every low platelet count, the doctor also looks at the blood under a microscope (a blood film) [1].
What platelet count is dangerous?
The lower the platelet count, the higher the risk of bleeding. This table is a general guide; if you are having chemotherapy or have a blood disease, your care team will tell you the numbers that apply to you.
| Platelet count (per microlitre) | What usually happens | What should I do? |
|---|---|---|
| Above 50,000 | Most people have no symptoms [1] | A mild fall (100,000 to 150,000) is usually re-tested after 4 to 6 weeks and a moderate fall (50,000 to 100,000) after 1 to 2 weeks [1] |
| 20,000 to 50,000 | Easy bruising, tiny red spots under the skin and longer bleeding after a small knock or cut [1] | See a doctor within the next few days |
| Below 10,000 | High risk of spontaneous bleeding [1] | Go to hospital the same day; admission and urgent assessment are usually needed [1] |
Before major surgery, the platelet count usually needs to be at least 40,000 to 50,000 [1].
Low platelets during chemotherapy
Chemotherapy and some targeted therapies can lower the platelet count [2]. This fall is usually temporary: platelets reach their lowest point a few weeks after each cycle and then come back up. For example, with the drug carboplatin the lowest count is usually around day 21, and by day 28 the platelet count of 9 in 10 patients is back above 100,000 [5].
While your platelets are low, take care to avoid bleeding [2]:
- Use a very soft toothbrush and an electric shaver instead of a razor, and wear shoes even at home.
- Do not take aspirin or ibuprofen without asking your doctor; these medicines increase the risk of bleeding.
- Cut down on alcohol or stop drinking it.
- If bleeding starts, press firmly with a clean cloth until it stops, and put ice on bruises.
Full guide: Low blood counts and preventing infection.
Minimum platelet count for chemotherapy
A blood count (CBC) is done before every cycle. The number needed is not the same for every drug, and the doctor takes it from each drug's prescribing information: for example, the platelet count needs to be at least 100,000 for carboplatin [5] and at least 75,000 for oxaliplatin [6]. If the count is still low, the doctor delays the cycle until the platelets recover, or lowers the dose for later cycles [5, 6].
For someone who is not bleeding, a platelet transfusion is usually needed only when the count is below 10,000; if you are bleeding, platelets may be given at a higher count [1, 4]. Some procedures need a higher number: if the count is below 20,000 before a lumbar puncture (spinal tap), or below 50,000 before major surgery, platelets are given beforehand [4].
Which foods raise the platelet count?
Many patients ask which foods will raise their platelet count. A low count caused by chemotherapy usually comes back up gradually as the bone marrow recovers [5], and what decides the treatment plan is the platelet count before each cycle [5, 6]. These points help:
- If the low count is due to a lack of vitamin B12 or folic acid, the deficiency should be treated as your doctor prescribes [1].
- Avoid alcohol [2].
- Before you take any supplement, vitamin or herbal product, tell your doctor; some of these products can change how cancer treatment works [12].
On eating during treatment, read: What to eat before and after chemotherapy and Foods to avoid during chemotherapy
High platelet count: what causes it?
A platelet count above 450,000 is called a "high platelet count" (thrombocytosis); some laboratories and studies use a cut-off of 400,000 [1, 9]. In most people, a high count is the body's reaction to another problem. In a study of 732 patients with a count of 500,000 or more, almost 9 in 10 had this kind of "reactive" high count [7]. The most common causes [7, 8]:
- Tissue damage, such as surgery or an injury
- Infection
- Long-term inflammation
- Iron deficiency
- Cancer
On its own, a reactive high count does not usually raise the risk of blood clots unless there is another risk factor as well [7].
Essential thrombocythaemia: when the bone marrow itself makes too many platelets
In a smaller number of people, the cause lies in the bone marrow itself. The most common of these conditions is essential thrombocythaemia: a slow-growing disease from the "myeloproliferative neoplasm" family in which the bone marrow makes too many platelets [10]. In about 8 in 10 patients, a change is found in one of the genes JAK2, CALR or MPL [10]. The main risk of this disease is blood clots, and treatment is mostly aimed at preventing clots: low-dose aspirin and, for people at higher risk, medicines such as hydroxyurea [10]. Most patients live with this disease for many years [10]. Read more: What are myeloproliferative neoplasms?
Can a high platelet count be a sign of cancer?
Sometimes a high platelet count is the first sign of a cancer that has not yet caused other symptoms [9]. In a large English study of people aged 40 or over with a platelet count above 400,000, about 1 in 9 men and 1 in 16 women were diagnosed with cancer within a year. When the count was also high on a second test within 6 months, this rose to about 1 in 5 to 6 men and 1 in 10 women [9]. The most common cancers were lung and bowel cancer, and a third of the people with one of these two cancers had no other sign of cancer [9].
So most people with a high platelet count do not have cancer, but a persistently high count in an adult is worth investigating. Depending on your age and symptoms, the doctor may consider [11]:
- A chest X-ray to check the lungs, for people aged 40 or over
- An endoscopy of the stomach and oesophagus, for people aged 55 or over who have nausea, vomiting, weight loss, reflux, indigestion or upper abdominal pain together with a high platelet count
- An ultrasound scan of the womb, for women aged 55 or over who have unusual vaginal discharge
Read more: Can a blood test detect cancer?
When should I contact a doctor?
Most changes in the platelet count have a simple cause. But:
Go to an emergency department straight away or call your local emergency number if [1, 2]:
- You have bleeding that does not stop after a few minutes of pressure
- You vomit blood, your stools are black or bloody, or your urine is red or pink
- You have a severe headache, changes in your vision, confusion or unusual drowsiness
Contact your doctor the same day if:
- Your platelet count is below 10,000; you usually need to be assessed in hospital the same day [1]
- A low platelet count comes with anaemia or an abnormal white cell count [1]
- You notice many tiny red or purple spots on your skin, or bleeding from your gums or nose [2]
- A few days after starting heparin injections, your platelet count has dropped or an arm or leg has become painful and swollen [1]
See a doctor within the next few days if:
- A high platelet count stays high on a repeat test, especially if you are 40 or over or have a persistent cough, weight loss or digestive problems [9, 11]
If you are having chemotherapy, learn the other warning signs too: Fever and warning signs after chemotherapy.
Frequently asked questions
My platelet count is slightly low but I feel well; should I worry?
Usually not. If your count is 100,000 to 150,000 and you have no symptoms, the doctor usually repeats the test after 4 to 6 weeks and checks your medicines, recent infections, liver disease and pregnancy [1]. The first step is also to make sure the platelets have not simply clumped together in the test tube [1]. To read the rest of your results, see Understanding your CBC results.
Can low platelets be a sign of leukaemia?
Usually not; infections, medicines and liver disease are more common causes [1]. But when a low platelet count comes with anaemia or an abnormal white cell count, urgent assessment is needed [1]. Read: Signs of leukaemia in a CBC blood test
What is ITP? Is it cancer?
ITP (immune thrombocytopenia) is not cancer; it is a disease in which the immune system destroys the body's own platelets [1]. In newly diagnosed adults without serious bleeding, a count of 30,000 or more is usually just monitored, and below that a short course of a steroid medicine is usually given [3]. For children with no bleeding, or only bruising and tiny spots on the skin, monitoring without medicine is also suggested [3].
Are low platelets during chemotherapy dangerous?
Most of the time this is a temporary, expected fall that the care team checks before every cycle [2, 5]. The risk of serious bleeding is mainly when the count is below 10,000; in that case platelets are usually transfused [1, 4]. Tell your care team at once about any bleeding that will not stop [2].
Can a high platelet count cause a stroke or blood clots?
What does a high platelet count with anaemia mean?
Iron deficiency can both cause anaemia and raise the platelet count [8]. Iron-deficiency anaemia in an adult is a reason to check the bowel with a stool test [11]. Read: Can anaemia be a sign of cancer?
Thresholds and guidelines (for doctors)
For physicians
Assessing thrombocytopenia. Platelets below 150 × 103/μL (mild 100 to 150, moderate 50 to 99, severe below 50). First exclude pseudothrombocytopenia with a citrate or heparin sample and a manual count; a peripheral blood smear for every patient. Repeat testing after 4 to 6 weeks when mild and 1 to 2 weeks when moderate. Admission and immediate evaluation for: major bleeding, platelets below 10 × 103/μL, evidence of haemolysis on the smear, new neurological or renal dysfunction, recent heparin exposure, associated coagulation abnormalities or vascular findings; also when accompanied by anaemia, leucopenia or leucocytosis. HIT in 0.2% to 5% of exposed patients: a fall of more than 50% in the platelet count 5 to 10 days after exposure, thrombosis in up to one-third; stop heparin and start a non-heparin anticoagulant immediately. Gestational thrombocytopenia accounts for 80% of thrombocytopenia in pregnancy (usually above 80 × 103/μL, from the second trimester; resolves after delivery). A minimum of 40 to 50 × 103/μL for most major invasive procedures and surgery [1].
ITP (ASH 2019). Newly diagnosed adults who are asymptomatic or have minor mucocutaneous bleeding: platelets 30 × 109/L or more, observation rather than corticosteroids (strong recommendation, very low certainty); below 30 × 109/L, corticosteroids (conditional recommendation). A short course (6 weeks or less) of prednisone 0.5 to 2.0 mg/kg/day or dexamethasone 40 mg/day for 4 days; admission suggested for newly diagnosed patients with platelets below 20 × 109/L. Newly diagnosed children with no or minor bleeding: observation rather than IVIG or anti-D (strong) and rather than corticosteroids (conditional). Second line in ITP lasting 3 months or more that is corticosteroid-dependent or unresponsive: a thrombopoietin receptor agonist, rituximab or splenectomy (preferably at least one year after diagnosis) [3].
Platelet transfusion (AABB/ICTMG 2025). Non-bleeding hypoproliferative thrombocytopenia during chemotherapy or allogeneic transplant: transfuse below 10 × 103/μL (strong recommendation); adults undergoing autologous transplant or with aplastic anaemia: no routine prophylaxis. Lumbar puncture below 20; central venous catheter at a compressible site below 10; low-risk interventional radiology below 20 and high-risk below 50; major non-neuraxial surgery below 50 × 103/μL. Dengue without major bleeding: transfusion not recommended [4].
Cycle thresholds in the FDA labels. Carboplatin: repeat a course only with neutrophils at least 2,000 and platelets at least 100,000 per mm3; thrombocytopenia below 50,000 in 25% of patients (single agent) with a nadir around day 21; dose adjusted to the nadir of the previous course (platelets below 50,000 or neutrophils below 500: 75% of the dose) [5]. Oxaliplatin: delay until neutrophils are 1.5 × 109/L or more and platelets 75 × 109/L or more; reduce the dose after grade 3 to 4 thrombocytopenia [6].
Thrombocytosis. In 732 patients with platelets of 500 × 109/L or more, 87.7% had secondary and 12.3% primary thrombocytosis (ET in 45% of primary cases); secondary causes: tissue damage 42%, infection 24%, malignancy 13% and chronic inflammation 10%. Arterial and venous thrombosis was more frequent in primary thrombocytosis; in secondary thrombocytosis it was only venous and occurred with other risk factors [7]. CPRD cohort (40,000 patients aged 40 or over with platelets above 400 × 109/L and 10,000 controls): 1-year cancer incidence 11.6% vs 4.1% in men and 6.2% vs 2.2% in women; 18.1% and 10.1% with a second raised count within 6 months; mostly lung and colorectal; one-third of patients with lung or colorectal cancer had no other symptoms [9]. NICE NG12: urgent chest X-ray at 40 or over with thrombocytosis (1.1.3); non-urgent upper GI endoscopy at 55 or over with a raised platelet count plus nausea, vomiting, weight loss, reflux, dyspepsia or upper abdominal pain (1.2.3 and 1.2.9); ultrasound for endometrial cancer at 55 or over with vaginal discharge plus thrombocytosis (1.5.13) [11]. ET: platelets 450 × 109/L or more and exclusion of other myeloid neoplasms (prefibrotic MF, PV, CML and MDS with ring sideroblasts and thrombocytosis); a JAK2, CALR or MPL driver mutation in about 80%; median survival about 18 years; thrombosis risk stratified by age over 60, thrombosis history and JAK2 mutation; low-dose aspirin, and cytoreduction for high-risk disease (hydroxyurea or pegylated interferon alfa first line) [10].
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