I agree with you, summers are really hot here. But be cool, your son is not having anything serious. Your lab reports don't point to urinary tract infection
can result in burning micturition, high coloured (dark yellow) urine, passing less frequent and small amount of urine. So check if he has other above mentioned symptoms. Easy way to check if its due to summer heat is to give plenty of fluids, juices, water, tender coconut water. If he starts passing more frequently large volume of urine and his burning micturition improves, then its probably due to dehydration in summer heat.
If problem doesn't subside even after one day of good amount of fluids, urinary tract infection should be suspected. He might need urine cultures as it is more informative than urine routine which you have already done. Need for antibiotics will be decided by your pediatrician
So your child's problem is probably due to dehydration. A small chance of urinary infection is there but it gets cured very well with antibiotics. So nothing much serious to worry about. Tak care.
Dr. C. Balaji