A “wee bag” is the common, informal term for a pediatric urine collection bag, also known as a U-bag. This device is a small, sterile, disposable plastic pouch designed to collect a urine sample from a non-toilet-trained child for laboratory analysis. The bag features an adhesive strip around an opening that adheres to the genital area, creating a temporary, leak-proof seal. This non-invasive method secures a sample from infants and toddlers who cannot urinate into a standard collection cup. The bags are designed for use on both male and female infants, typically holding 100 to 200 milliliters for a single specimen.
Why Urine Collection Is Necessary
Healthcare providers request a urine sample to investigate health issues in infants and young children. The most frequent reason is to screen for a suspected urinary tract infection (UTI), especially when a child presents with a fever of unknown origin. Untreated infections can potentially lead to kidney scarring and long-term renal issues.
Urine testing also provides valuable information about overall kidney function, detects signs of dehydration, or identifies systemic conditions like diabetes or metabolic disorders. The bag collection method is often selected as a convenient initial screening step when the suspicion of a serious infection is low.
Step-by-Step Application Guide
Successful collection requires meticulous skin preparation to ensure the adhesive seal holds and minimize contamination. The genital area must be thoroughly cleaned with soap and water or a sterile wipe, avoiding creams, oils, or powders. For female infants, cleanse from front to back, cleaning the skin folds around the vulva. For male infants, clean the end of the penis, gently retracting and cleaning the foreskin if uncircumcised. Allow the area to air dry completely.
Next, peel the backing paper from the adhesive, taking care not to touch the sticky surface. For female infants, place the bag opening over the vulval area, securing the adhesive from the area between the rectum and the vaginal opening upwards.
For male infants, the penis is placed entirely inside the bag opening, and the adhesive is firmly pressed onto the skin around the scrotum. Loosely fit a clean diaper over the bag, ensuring the collector is not pulled or tugged. Once urine is collected, gently remove the bag and immediately transfer the contents to the sterile laboratory container provided.
Reliability Concerns and Other Sample Methods
The main drawback of the collection bag method is the high risk of sample contamination, which occurs when skin bacteria or genital flora enter the bag along with the urine. Contamination rates for U-bags can be as high as 30% to 80%, often leading to false-positive results for urinary tract infections (UTIs). Due to this unreliability, professional guidelines advise against using a bag specimen for a urine culture that confirms a UTI diagnosis.
If the initial bag sample suggests an infection, a more reliable collection method is required for confirmation. Less invasive alternatives include the “clean catch” stimulation method, where a healthcare provider attempts to catch a midstream sample after stimulating the infant to void. When a sterile sample is mandatory, medical professionals use invasive techniques. These include urethral catheterization, where a small tube is temporarily inserted into the bladder, and suprapubic aspiration, the gold standard for a fully sterile sample, which involves inserting a needle directly into the bladder through the lower abdominal wall.