From the Guidelines
A clean catch urine sample can still be valid for a woman who is menstruating, but special precautions should be taken to minimize menstrual blood contamination. According to the most recent and highest quality study available, which is from 2010 1, asymptomatic bacteriuria can be reliably detected through urine culture, and the presence of at least 10^5 colony-forming units per mL of urine of a single uropathogen, in a midstream clean-catch specimen, is considered a positive test result. To ensure the validity of the sample, women should use a tampon before collecting the sample to prevent blood from entering the urine specimen. The proper clean catch technique remains essential:
- Thoroughly wash hands
- Cleanse the genital area from front to back with antiseptic wipes
- Start urinating into the toilet
- Then collect the midstream portion in a sterile container without touching the inside of the cup or lid. If visible blood contamination occurs despite these precautions, it's best to inform the healthcare provider and potentially reschedule the test if possible. Menstrual blood in the sample can affect certain test results, particularly by introducing red blood cells, protein, or bacteria that aren't actually present in the urine, potentially leading to false positive results. For some tests like pregnancy tests or certain infection screenings, even a slightly contaminated sample may still provide accurate results, but this depends on the specific test being performed. The guidelines for asymptomatic bacteriuria in adults, as stated in the 2005 study 1 and reaffirmed in the 2010 study 1, emphasize the importance of proper urine specimen collection to minimize contamination.
From the Research
Validity of Clean Catch Urine for Women Having Menses
- The validity of a clean catch urine sample for women having menses is a topic of debate, with some studies suggesting that the midstream clean-catch technique may not be necessary for accurate results 2, 3.
- A study published in 2000 found that the contamination rates for midstream clean-catch urine samples were similar to those for urine samples collected without cleansing, suggesting that the midstream clean-catch technique may not be beneficial in reducing contamination 2.
- A systematic review published in 2023 found that there was no difference in contamination rates between midstream clean-catch urine samples and random voiding samples, and that the midstream clean-catch technique may not be better than other methods for collecting urine samples 3.
- However, a study published in 1989 found that midstream clean-catch urine sampling was comparable to catheterization in terms of urinalyses and urine cultures, but this study excluded women with active vaginal bleeding 4.
- Another study published in 2021 found that clean catch urine samples can be used to diagnose chlamydia and gonorrhea in adolescent females, with high sensitivity and specificity 5.
- It is worth noting that the presence of menses may affect the accuracy of urine test results, and some studies suggest that urine samples should be collected when the patient is not menstruating 4.
- Overall, the evidence suggests that a clean catch urine sample may be valid for women having menses, but the results should be interpreted with caution and in the context of the individual patient's symptoms and medical history 2, 3, 5, 6, 4.