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What initial investigations should I perform for a patient presenting with thrombocytopenia?

Answer

Guideline-Aligned (High Confidence)

Generated by iatroX. Developer: Dr Kola Tytler MBBS CertHE MBA MRCGP (General Practitioner).

Last reviewed: 16 August 2025

Initial Investigations for Thrombocytopenia

The primary initial investigation for a patient presenting with thrombocytopenia is a full blood count (FBC) ¹,²,⁴,⁶. This should be considered very urgent (within 48 hours) if there is unexplained bleeding, bruising, or petechiae ⁴.
A comprehensive assessment should be conducted to determine the possible underlying cause of the thrombocytopenia ¹. This includes reviewing the patient's medical history and current medications, as some medicines can be associated with thrombocytopenia ¹.
If a bleeding disorder is suspected, or if there is abnormal bruising, an abnormal clotting screen may be considered as part of further investigations ². For women with heavy menstrual bleeding, testing for coagulation disorders (e.g., von Willebrand's disease) should be considered if they have had heavy menstrual bleeding since their periods started and have a personal or family history suggesting a coagulation disorder ⁶.
Depending on the initial platelet count and clinical context, a repeat full blood count may be arranged ¹. For instance, if the platelet count is 50–100 × 10^9/L without other referral criteria, a repeat FBC in 1–2 weeks may be appropriate ¹. If a platelet count is 100–150 × 10^9/L with no underlying cause identified, a repeat FBC in 4–6 weeks is suggested ¹. If a medicine is suspected to be the cause, the count should be reviewed and repeated in 1–2 weeks after considering stopping the medicine ¹.