At almost 4 I think it would be quite difficult to tell the difference. I had no idea that ds1 had ADHD at that age and I would have been hard pushed to say that ds3 didn't. They were both very "active" boys.
Looking back it was the strange things that marked ds1 as different. He was a happy baby and loved everyone. He would hold his arms up to strangers to be lifted, he never had a 'clingy' phase and he showed no particular preference for me although I was his main carer.
He dribbled, and I mean dribbled. The whole front of his t-shirt would be soaked, much like a teething baby but was just as bad at 4.
He was always the child that spilt his drink no matter where we were. We could be with friends with much younger children and I could guarantee whose drink would go over. It became a bit of a joke.
He appeared very clever. He could count to 100 before he was 2 and shortly afterwards could read all the numbers on the street doors as we passed. I thought he was a genius but I now think that wasn't normal. He couldn't figure out jigsaws at all.
He simply couldn't follow instructions. I knew he wasn't really naughty but he just didn't seem able to do as he was asked. He was the same where ever he was and whoever he was with.
In comparison ds3 is boisterous, doesn't alwast do as I ask him but always does as his teacher says. Is a monster at home and a little delight at school/after school club.
What concerns do you have?