Biomarker · Blood cells

Platelets

Also known as: platelet count, thrombocytes, PLT

Small cell fragments that plug damaged vessel walls and start the clotting cascade. Too few (thrombocytopenia) and the person bruises and bleeds; too many (thrombocytosis) is usually a reaction to inflammation, bleeding or iron deficiency.

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Also known as: platelet count, thrombocytes, PLT
Units: ×10⁹/L
Measured by: Full blood count

What it is and what it does

Platelets bud off from giant marrow cells called megakaryocytes and survive for about 7 to 10 days, with a third held in the spleen. When a vessel is injured they stick to the exposed wall, activate, clump together and provide the surface on which clotting factors assemble. The count is part of the full blood count. Bleeding from a low count usually appears as pinpoint spots (petechiae), bruises, nosebleeds and gum bleeding; spontaneous serious bleeding becomes a risk below about 20 ×10⁹/L. Antiplatelet medicines such as aspirin change how platelets work without changing the count.

Why it may be higher

Reactive: infection, inflammation, surgery, bleeding, iron deficiency, cancer
After the spleen is removed
Essential thrombocythaemia and other myeloproliferative disorders

Why it may be lower

Immune thrombocytopenia (antibodies destroy platelets)
Medicines: heparin, some antibiotics, chemotherapy, sodium valproate, alcohol
Liver disease and an enlarged spleen (platelets pooled in the spleen)
Bone-marrow failure, B12 or folate deficiency, leukaemia
Sepsis, disseminated intravascular coagulation, pregnancy (mild), some viral infections

A high or low value can be associated with several different situations. The result is interpreted with other results, symptoms, history and clinical findings.

What can affect the result

Platelets can clump in the tube and read falsely low (pseudothrombocytopenia): a repeat in a different tube or a blood film settles it
Recent surgery, infection or iron deficiency raises the count
Pregnancy lowers it slightly

Reference ranges. Reference intervals for this marker depend on the laboratory, the assay, the units, age, sex and pregnancy. Interpret a result against the interval printed on the laboratory report, not against a figure from the internet.

Medicines that can change it

Aspirin Ibuprofen

Each medicine page lists its effect on this marker under "Effects on tests and results", with the source.

Educational content. A biomarker page explains what a substance is and why its level can change. It cannot determine the cause of your result: interpret a result using the range supplied by the laboratory that performed the test, with the clinician who ordered it.