Final answer:
The diagnosis for a kid with hematuria and flank pain radiating to the groin is likely renal calculi. The best test to confirm this diagnosis is a computed tomography (CT) scan.
Step-by-step explanation:
The likely diagnosis for a kid with hematuria and flank pain radiating to the groin is renal calculi, also known as kidney stones. These are formed when minerals and salts in the urine crystallize and form solid masses. A specific test called a computed tomography (CT) scan is considered the best diagnostic method for detecting kidney stones. The CT scan uses X-rays to create detailed images of the urinary tract and can accurately identify the presence, size, and location of kidney stones.