Urine testing is an important diagnostic tool in healthcare, providing insights into various health conditions. These tests can help detect issues ranging from kidney problems to urinary tract infections (UTIs). For accurate results, however, the urine sample must be collected properly. Sometimes, these samples can become contaminated, meaning they contain unintended substances that interfere with the test’s reliability.
What Contamination Means
A contaminated urine sample contains foreign substances not naturally part of the urine or originating from the urinary tract. These often include bacteria, skin cells, or other external matter, such as squamous epithelial cells. It is important to distinguish contamination from an actual urinary tract infection. Contaminated samples may show bacteria, but these are typically from the skin or genital area, not multiplying within the bladder. If a urine culture shows the growth of several different types of bacteria, it typically suggests contamination rather than a single infecting organism.
How Urine Samples Become Contaminated
Urine samples often become contaminated due to improper collection techniques. Inadequate cleaning of the genital area before urination is a frequent cause, allowing bacteria, yeast, or other microorganisms from the skin to enter. Vaginal discharge, menstrual blood, or fecal matter can also introduce contaminants. Touching the inside of the collection cup or lid, or using non-sterile containers, can introduce external bacteria or compromise integrity. Delays in transport or improper storage, like leaving the sample at room temperature, can lead to bacterial overgrowth, making it difficult to distinguish contaminants from infection-causing organisms.
Why Contamination Matters
Contaminated urine samples lead to inaccurate or misleading test results. This can cause false positives, where a person is incorrectly diagnosed with an infection, potentially leading to unnecessary antibiotic treatment. Such misdiagnosis may delay proper treatment for underlying health issues and contribute to antibiotic resistance. The most common outcome is the need for a retest, causing inconvenience and delays for patients and healthcare providers. Studies indicate that up to one in four urine samples may be contaminated, highlighting the widespread nature of this issue.
Ensuring a Clean Urine Sample
To minimize contamination, follow these steps for collecting a “clean-catch” urine sample:
- Wash your hands thoroughly with soap and water.
- For individuals with a penis, clean the tip of the penis with a sterile wipe, pulling back the foreskin if uncircumcised.
- For individuals with a vagina, spread the labia and clean the area around the urethra from front to back using sterile wipes.
- Urinate a small amount into the toilet first to flush away bacteria near the urethral opening.
- Without stopping the flow, place the sterile collection cup into the urine stream and collect the sample until it is about half full.
- Do not touch the inside of the cup or lid, or allow the cup to touch your skin.
- After collection, finish urinating into the toilet, securely close the lid, and wash your hands again.
- Deliver the sample to the laboratory as soon as possible, ideally within two hours, or refrigerate it if there is a delay.