Explainer · updated 2026-11-09
Platelets, explained in plain English
Key facts
- Typical adult reference interval: 158-424 x10^3/uL (HRI-HR)
- Level above which a count counts as raised: about 450 x10^3/uL (Bleeker 2011)
- What platelets do: clump together to plug a cut and start a clot (Bleeker 2011)
- The medical name for a low count: thrombocytopenia (Bleeker 2011)
What it is
Platelets are the small cell fragments that clump together to plug a cut and start a clot. They are counted on every routine blood count. Both a high and a low count get looked into.
What the number is telling you
The count is read beside the other rows of the blood count and beside your previous counts. A single high reading is often repeated, because infection, inflammation and iron deficiency can raise it for a while and then settle.
What high or low can mean
High: Above about 450 thousand per microlitre is thrombocytosis, the count that guidelines use to define a raised result. Most cases are reactive: the marrow is answering an infection, inflammation, tissue damage or iron deficiency. A smaller number come from a problem in the marrow itself.
Low: A low count is thrombocytopenia. The marrow may be making fewer platelets, or the body may be destroying or pooling them faster than usual.
What a typical result looks like
The harmonized adult interval from the HRI-HR set runs from 158 to 424 thousand per microlitre. The range on your own report is the one that counts.
Questions worth asking your doctor
- Was this count repeated, and did it stay high?
- What in my recent history could explain it?
- Do my other blood count rows point anywhere?
- How does this compare with my previous counts?
If a result worries you, ask your doctor.
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