Prospective studies on the use of a bag applied to the perineum for urine collection have shown a high incidence of false-positive culture results, ranging from 85% to 99%. Bagged specimens, when collected appropriately, may be used for screening urinalysis as a first step when a UTI is suspected. If there are signs of infection, a properly collected urine culture should then be obtained. For children under two years of age, it is recommended to perform sterile-technique urethral catheterization. Alternatively, suprapubic bladder aspiration has been shown to have the highest sensitivity but requires skilled providers with ultrasound guidance, so is often not practical. In older children with sphincteric control, mid-stream clean-catch collection is possible and reliable. American Academy of Pediatrics, American Academy of Family Physicians, and European Association of Urology guidelines each issue this recommendation with the support of quality A evidence.