30th April 2024

A 35-year-old woman presents with a two-month history of persistent fatigue, easy bruising, and recurrent nosebleeds.

A 35-year-old woman presents with a two-month history of persistent fatigue, easy bruising, and recurrent nosebleeds. She has lost 5 kg over the last month without any changes in diet or exercise. She denies any history of significant illness and does not take any regular medications.

Investigations:

Haemoglobin: 95 g/L (120–160)

White cell count: 50 × 10^9/L (4.0–11.0)

Platelets: 50 × 10^9/L (150–400)

Peripheral blood smear: Presence of leukemic blasts

Creatinine: 90 μmol/L (45–84)

Lactate dehydrogenase (LDH): Elevated

Which initial investigation is most likely to help establish a diagnosis?