A 3 year old child brought by his mother. Examination: bruises on the buttocks. Mother also gives history of runny nose 2 weeks ago. What is the single most appropriate next action?

The key is B. Coagulation profile. [Henoch schonlein purpura occurs mostly in the winter months. About 50-90% of patients have a preceding upper respiratory tract infection (URTI). There is a symmetrical, erythematous macular rash, especially on the back of the legs, buttocks and ulnar side of the arms. Within 24 hours, the macules evolve into purpuric lesions, which may coalesce and resemble bruises. Plasma D-dimer - May be substantially increased. PT and aPTT - May be reduced (eg, hypoprothrombinemia)].