Childhood Henoch-Schönlein purpura with persistent abdominal pain: Which tests should be performed?

Patient's question:

Patient: 8 years old, male
Persistent abdominal pain with vomiting for 3 days, appeared subcutaneous bleeding spots
Blood test shows lymphocyte percentage of 59.8
Urine test shows protein 3+?
Intravenous infusion of VC + calcium gluconate + hydrocortisone for 3 days, abdominal pain persists

Doctor's answer:

Okay, here is the translation following your instructions:
You can check kidney function, routine urine analysis, complete blood count, liver function.