Platelets: Normal Values and What an Abnormal Count Means

Platelets, also called thrombocytes, are small cell fragments formed in your bone marrow. They are indispensable when it comes to stopping bleeding.

As soon as a blood vessel is damaged, platelets stick to the injury, clump together and form a first plug. They then set the clotting cascade in motion, which turns that soft plug into a firm, stable clot.

This test measures how many platelets circulate per litre of blood. The value is measured as standard in the complete blood count and says something about your ability to stop bleeding. It counts the platelets rather than testing how well they work, which is a separate question.

A low platelet count (thrombocytopenia) means bleeding is stopped less effectively. You notice it as bruises that form easily, small wounds that keep bleeding, bleeding gums or nosebleeds. Causes range from a viral infection and medication to an autoimmune reaction, a liver condition or an enlarged spleen.

A high count (thrombocytosis) is usually reactive: the body temporarily produces more platelets during inflammation, infection, iron deficiency or after surgery. Less often a bone marrow disorder underlies it. With strongly raised counts the risk of clot formation can increase.

The count says nothing about how well the platelets work. Anti-inflammatories such as aspirin and NSAIDs inhibit platelet function while the count stays normal.

Platelets are measured as standard in the complete blood count. Testing is particularly useful with bruising for no clear reason, small wounds that keep bleeding, bleeding gums, frequent nosebleeds or heavy periods.

The value is also checked before surgery or a procedure, and to follow up when an abnormal count was found before or when you take medicines that can affect production.

Because the count can be temporarily raised after an infection or inflammation, your doctor will often reassess an abnormal result at a later point.