If the sample was cloudy too, it might be due to pus cells, mucus etc associated with infection. Since you say he has burning sensation too, its likely to be due to an infection.
If its an infection, urine microscopy will show lot of pus cells and urine culture will confirm the organism and its sensitivity to antibiotics.
If its infection, your son will need appropriate antibiotics.
How ever it may due to other cause like protein in the urine, crystals like calcium, oxalate
or uric acid crystals.
If crystals are found in urine, your doctor will advise for further investigations.
Usually urine microscopy results are available the same day within few hours. Check with the lab.
Till then make him drink plenty of water, fruit juices etc. Fluids help in both infection and crystals.
Cranberry juice will be good for your son.
Hope my answer helps you.
Wish a speedy recovery for your son.