It is very important to get a clean specimen of urine. A midstream urine or clean catch sample (urine collected after the child has already started passing urine), a sample collected by passing a catheter into the bladder under aseptic methods or a suprapubic aspiration (best done with ultrasonography) are by far the best methods. Using a urine bag is very inaccurate and is should be avoided if possible.

Leukocytes, nitrites and protein, and sometimes blood, are typical findings when the urine is tested with a reagent strip. It is probably not a urinary tract infection if the reagent strip test on a sample of freshly passed urine is completely normal, i.e. negative for protein, nitrite, blood and leucocyte esterase.

Pus cells are usually present on a spun deposit of urine.

The only accurate way to confirm a urinary tract infection is a positive culture when the urine has been collected correctly. More than 100 000 bacteria/ml on a clean catch urine, more than 1 000 bacteria/ml on a catheter specimen or any bacteria on a suprapubic sample is abnormal.

It is very important to make an accurate diagnosis and not simply send a urine bag sample to the laboratory. A normal urine bag result will exclude a urinary tract infection but a positive result may simply be due to skin or stool contamination. A confirmed diagnosis is also important because it indicates that a series of management steps is required. Treating a presumed urinary tract infection without confirming the diagnosis is bad practice.