Platelet count (PLT)

What it measures

Counts platelets, the cell fragments that start blood clotting. Ordered for bleeding or bruising, before procedures and to monitor drugs and marrow disease.

Specimen and preparation

• Specimen: Whole blood (EDTA); citrate tube if EDTA clumping suspected
• Tube: Lavender top
• Preparation: Ensure a clean venipuncture and prompt mixing to avoid clots and clumping.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Reactive: infection, inflammation, iron deficiency
• After splenectomy or bleeding
• Essential thrombocythemia and other MPNs
• Malignancy

Causes of low values

• Immune thrombocytopenia (ITP)
• Dengue and other viral infections
• DIC, TTP, HUS
• Marrow failure or chemotherapy
• Hypersplenism and liver cirrhosis

Method

Impedance or optical counting on analyzer; smear estimate to confirm abnormal counts

Good to know

Always check the film for platelet clumps (EDTA pseudothrombocytopenia) before reporting a low count. Below 20 ×10⁹/L is usually critical. Consider heparin-induced thrombocytopenia if counts fall on heparin.

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