Final answer:
For a child peeing blood, the best initial test is a urinalysis, which helps identify the cause of blood in the urine. Depending on the findings, additional imaging tests or procedures may be required.
Step-by-step explanation:
The best test for a child experiencing hematuria (blood in urine) is usually a urinalysis. This simple test can provide a wealth of information and help determine the cause of the bleeding. It can identify if the blood is coming from a urinary tract infection, kidney disease, or other conditions. If necessary, further testing such as an ultrasound, CT scan, or cystoscopy might be recommended depending on the results of the urinalysis and the patient's other symptoms and medical history.