Thank you for your query.
Do not worry.
Every sickeness can cause minor proteinuria
I think your doctor is suspecting some urinary problem.So he wants to check it out throughly.
A small amount of urine can give erronous results.
I think you child is fine.
Consult your doctor if the problem persists.
If you have any further queries you are free to consult me.
Hope this answers your query.
Wishing a speedy recovery.
Have a nice day.