Platelet count

Also known as PLT, platelets, thrombocyte count

cell count · no single molecular formula

LOINC 777-3 code verified whole_blood 10*3/uL

What this substance is

A platelet is a cell fragment, not a compound. The cell type is recorded in the anatomy graph as CL:0000233; there is no molecular identity to give.

Reference ranges

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This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm. The platelet count is part of a complete blood count. You do not need to do anything special to get ready.

Platelet count is reported with the CBC on a K2 EDTA whole-blood venous sample; impedance analysers such as the Coulter DxH 800 derive PLT from the platelet histogram. Clotted specimens are rejected. No preparation is needed for a count, unlike platelet function tests, for which aspirin and ibuprofen may need to be stopped.

Where: laboratory

Sources: NHANES 2019-2020 Laboratory Procedure Manual: Complete Blood Count (Coulter DxH 800), CDC/NCHS; Platelet Tests -- MedlinePlus Medical Tests, U.S. National Library of Medicine cited · not yet checked by a person

In the lab

impedance

Electrical impedance count from platelet histogram

Platelets are tiny cell pieces that help blood clot. The machine counts them by the small electrical blips they make passing through a tiny hole.

Platelets are counted by impedance in the RBC aperture as particles of about 2 to 20 fL; the count is derived from the platelet histogram and multiplied by a calibration constant.

Read by: Electrical impedance pulses in the 2 to 20 fL size window

What can throw it off

Clumped platelets
Very small red cells near the upper threshold
Cell fragments and cellular debris

Why labs disagree: Platelet results are not interchangeable between measuring systems, even between systems that all use the impedance method, and one study noted that the reference range on Sysmex analysers seems lower than most textbook data. Platelet upper limits also differ markedly between men and women, so labs are advised to set intervals on their own analyser.

Sources: Arbiol-Roca A et al. Reference intervals for a complete blood count on an automated haematology analyser Sysmex XN in healthy adults from the southern metropolitan area of Barcelona. EJIFCC 2018 (PMC5949618, open access); CDC NHANES 2011-2012 Laboratory Procedure Manual: Complete Blood Count using Coulter HMX cited · not yet checked by a person

What it reports on

platelet structural component of
A platelet count is the number of platelets, small blood cells that help blood clot.
bone marrow synthesized by
Platelets are formed in the bone marrow, so a marrow problem can lower the count.
spleen stored by
The spleen stores platelets, and an enlarged spleen can hold or remove too many, lowering the count.

Associated symptoms

Conditions this marker features in

When low

low Low platelet count · defining
Thrombocytopenia is defined by the platelet count: below 150,000 per microlitre is lower than normal (NHLBI). Some clinicians use 100 × 10^9/L as the cutoff instead.
low Anaemia from red cells breaking down too fast · supportive
Checked to find the type of haemolytic anaemia. A low platelet count points to a clotting disorder of small vessels or Evans syndrome.

Ordered as part of

cbc