30th April 2024

A 7-year-old boy is brought to the clinic with a history of easy bruising and prolonged bleeding after minor injuries.

A 7-year-old boy is brought to the clinic with a history of easy bruising and prolonged bleeding after minor injuries. He recently developed a large, painful bruise on his thigh after a fall. There is no known family history of bleeding disorders.

Investigations:

Haemoglobin: 130 g/L (110–150)

White cell count: 6.0 × 10^9/L (4.0–12.0)

Platelets: 200 × 10^9/L (150–450)

Prothrombin time (PT): Normal

Activated partial thromboplastin time (aPTT): Prolonged

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