The most reliable urine specimen is obtained by:

Suprapubic aspiration avoids potential contamination Urinary Tract infection Most often, the urine is often obtained from a voided specimen. In children, who are not toilet trained, a urine collection device, such as bag, is placed over the genitals, and the urine is cultured from the bagged specimen Suprapubic aspiration avoids potential contamination; however due to its invasiveness, it is rarely used except in children and selected patients Urine obtained from a urinary catheter is less invasive than a suprapubic aspiration and is less likely to be contaminated than that from a voided specimen. Ref: Smith 18th edition Pgno: 200