Platelets, also known as thrombocytes, are small blood cells that circulate within our blood and bind together when they recognize damaged blood vessels, helping to form clots that prevent excessive bleeding. There is a normal range for platelet counts, and levels outside of this range can indicate certain medical conditions.
What is the normal platelet count?
A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood for adults. For children, the normal range is higher, from 150,000 to 500,000. Newborns have higher platelet counts as well, ranging from 150,000 to 350,000 at birth.
A platelet count below the normal range is called thrombocytopenia. This condition can occur for many reasons, from genetic disorders to particular medications. A mild drop in platelets may not cause any issues, but very low counts can lead to excessive bruising or bleeding.
A platelet count above the normal range is called thrombocytosis. This is rarer but can occur due to some bone marrow diseases, infections, inflammation, or certain tumors. Very high platelet counts may increase clot risk.
What are dangerously low platelet levels?
There is no single platelet count that is universally dangerous for all people. Those with mild thrombocytopenia may have no symptoms at all. However, platelet counts below 20,000 are considered life-threatening.
At levels below 10,000 platelets per microliter, spontaneous severe bleeding is likely. This can include bleeding gums, nosebleeds, extensive bruising, blood in urine or stool, and heavy menstrual bleeding in women.
When the platelet count drops below 5,000, internal bleeding in the brain or other organs becomes much more likely. At these dangerously low levels, any minor bump can cause substantial internal bleeding that may become life-threatening without rapid treatment.
Symptoms of very low platelet counts
- Bleeding gums
- Red or purple dots on skin (petechiae)
- Easy bruising
- Blood in urine or stool
- Heavy menstrual bleeding
- Prolonged bleeding from cuts
- Dizziness, headaches, or blurred vision from potential internal bleeding
What causes low platelet levels?
There are many potential causes of low platelet levels, including:
Decreased platelet production
- Aplastic anemia – Bone marrow cannot produce enough blood cells
- Leukemia – Cancer of bone marrow cells
- Vitamin deficiencies – Lack of vitamin B12 or folate
- Infections – HIV, hepatitis C, mononucleosis
- Genetic disorders – Fanconi anemia, Wiskott-Aldrich syndrome
Increased platelet destruction
- Idiopathic thrombocytopenic purpura (ITP) – Antibodies destroy platelets
- Thrombotic microangiopathies – Blood clots form in small vessels
- Hemolytic uremic syndrome – Can occur after intestinal infection
- Preeclampsia – Pregnancy complication involving high blood pressure
- Certain medicines – Heparin, quinine, sulfa antibiotics
- Autoimmune disorders – Lupus, rheumatoid arthritis
Sequestration of platelets
- Enlarged spleen – Traps and destroys platelets
- Cirrhosis – Platelets trapped in scarred liver
- Bone marrow cancers – Crowd out normal platelet production
How are low platelet levels diagnosed?
Low platelet levels are diagnosed with a complete blood count (CBC) test. This simple blood test measures levels of platelets as well as other blood components like red blood cells and white blood cells.
If a CBC shows abnormally low platelet counts, further testing can help determine the underlying cause:
- Bone marrow biopsy – Examines marrow directly for problems
- Genetic testing – Checks for inherited disorders
- Imaging tests – CT, ultrasound, or MRI to identify enlarged spleen
- Antibody tests – Help diagnose autoimmune disorders
How are dangerously low platelets treated?
Treatment depends on the cause and severity of thrombocytopenia. Options may include:
Treating underlying disorders
If a specific condition like leukemia or vitamin deficiency is causing low platelets, treating the underlying problem may help platelet levels recover.
For sudden, severe drops in platelets, a transfusion of platelets isolated from donor blood can temporarily increase levels. This helps prevent serious bleeding while other therapies take effect.
Surgically removing the spleen can treat thrombocytopenia caused by an enlarged spleen trapping too many platelets.
Immunosuppressants and corticosteroids
Medications that suppress the immune system may help increase platelet counts in disorders where antibodies are destroying platelets, like ITP.
This procedure filters the blood to remove antibodies attacking platelets. It may be used for thrombotic microangiopathies like hemolytic uremic syndrome.
What are dangerously high platelet levels?
Platelet counts above 1,000,000 per microliter are considered extremely elevated. While high counts alone may cause no issues, very high levels can significantly increase the risk of potentially fatal blood clots.
Symptoms of very high platelet counts
- Blood clots in veins – Deep vein thrombosis, pulmonary embolism
- Heart attack
- Transient ischemic attacks (mini-strokes)
- Redness, warmth, and pain in extremity (clot)
- Sudden vision changes, slurred speech, weakness on one side (stroke warning signs)
- Chest pain, pressure (heart attack warning sign)
What causes high platelet levels?
Some potential causes of elevated platelet counts include:
- Iron deficiency anemia
- Chronic inflammatory conditions
- Tissue damage – Burns, surgery, injuries
- Infections – Tuberculosis, hepatitis, HIV
- Cancers – Leukemia, lymphoma, other bone marrow cancers
- Polycythemia vera – Bone marrow disorder
- Essential thrombocythemia – Bone marrow disorder
- Certain genetic mutations
How are high platelet levels diagnosed?
As with low platelets, a CBC blood test can detect increased platelet counts. Other tests may include:
- Blood smear examination – Analyzes blood cell appearance
- Genetic testing – For mutations like JAK2
- Bone marrow biopsy – Evaluates marrow for cancer or disorders
- Imaging tests – Help identify causes like infection
How are dangerously high platelets treated?
Treatment depends on the underlying cause but may include:
- Treating underlying conditions – Targeting infections or inflammation
- Aspirin or anti-clotting drugs – Reduces blood clot risk
- Hydroxyurea – Lowers platelet production
- Interferon alfa – Suppresses bone marrow
- Plateletpheresis – Filters excess platelets from blood
- Chemotherapy – For cancers and bone marrow disorders
- Splenectomy – Removes enlarged spleen trapping cells
When to seek emergency care for platelet abnormalities
Seek immediate medical care if you experience:
- Severe bleeding symptoms – Extensive bruising, nosebleeds, bloody urine/stool
- Sudden one-sided weakness, vision changes, slurred speech – Signs of stroke
- Chest pain, pressure, shortness of breath – Heart attack warning signs
- Swelling, pain, warmth in an extremity – Potential blood clot
- Severe headaches, confusion, vision changes – May indicate brain bleeding
Prompt emergency care can help stabilize dangerously high or low platelet counts before serious complications develop.
Platelet counts outside the normal range can occur for many reasons. Mildly abnormal levels may cause minimal symptoms or none at all in some cases. However, severely high or low platelet counts can lead to potentially fatal bleeding or clotting complications.
Levels below 20,000 or above 1,000,000 are considered medical emergencies requiring rapid treatment. Monitoring platelet counts with routine blood work allows early detection of any concerning changes so that appropriate treatment can be started before a crisis develops.