Yes, you can do a urine test while on your period, but menstrual blood can contaminate the sample and skew certain results. Whether that matters depends on the type of test. A drug screening won’t be affected at all, while a standard urinalysis or urine culture is more likely to come back with misleading findings. The good news is that simple collection techniques can minimize the problem, and your doctor can account for your cycle when reading results.
Which Tests Are Affected and Which Aren’t
Menstrual blood introduces red blood cells, white blood cells, and protein into your urine sample. These are the exact markers a standard urinalysis measures to check for kidney problems, urinary tract infections, and other conditions. When menstrual blood mixes in, a dipstick test can show false positives for blood in the urine, elevated protein, and higher-than-normal white blood cell counts. That can make it look like you have an infection or kidney issue when you don’t.
Drug tests are a different story. These screenings look for specific drug metabolites, not blood cells or protein. Menstrual blood doesn’t interfere with the chemistry involved, so your results will be accurate regardless of where you are in your cycle. The same applies to most hormone-based blood draws, though if you’re taking a urine pregnancy test, know that the hormone it detects (hCG) isn’t affected by menstrual blood either. In fact, the FDA notes that getting your period when you didn’t expect it is itself a sign that a negative pregnancy result was correct.
How Menstrual Blood Skews Urinalysis Results
A urinalysis uses a paper dipstick that changes color when it reacts with certain substances. Even a tiny amount of menstrual blood can trigger the hemoglobin indicator on the strip, producing a false-positive result for blood in the urine. This is a well-documented problem: research labs routinely exclude urine samples from menstruating patients in studies specifically because of erythrocyte (red blood cell) contamination.
Vaginal discharge and mucus can cause additional confusion. These secretions contain white blood cells and bacteria that mimic the signs of a urinary tract infection on a dipstick. If your doctor ordered the test to check for a UTI, contamination from menstrual blood and discharge can make the results unreliable. The concern isn’t just false positives. According to NIH clinical guidelines, women with blood in their urine are already the most likely group to receive incomplete evaluations, partly because doctors can’t always tell whether the blood came from the urinary tract or the vagina.
How to Collect a Clean Sample
If you need to provide a urine sample during your period, the goal is to keep menstrual blood out of the cup. Cleveland Clinic’s collection guidelines recommend inserting a fresh tampon before you begin. This blocks the flow of menstrual blood during the collection process. If you don’t use tampons, a menstrual cup or disc serves the same purpose.
After that, follow the standard clean-catch method:
- Clean the area. Separate the skin folds around your urinary opening and wipe from front to back with the provided antiseptic towelettes. Use a fresh towelette each time, repeating two to three times.
- Start in the toilet. Urinate for a few seconds before placing the cup into the stream. The first burst of urine carries the most bacteria and debris from the skin.
- Catch midstream. Fill the cup about halfway, then finish urinating into the toilet.
This technique significantly reduces contamination, though it doesn’t eliminate it entirely. Some blood may still reach the sample, especially during heavy flow days.
Should You Reschedule the Test?
It depends on why the test was ordered. For routine urinalysis or a suspected UTI, rescheduling to a time when you’re not menstruating gives the cleanest results. NIH guidelines note that when doctors need to evaluate blood in the urine, menstruating patients should ideally be “reevaluated when the gynecologic bleeding has resolved.” If the test can wait a few days without causing harm, that’s often the simplest solution.
If rescheduling isn’t practical, or if you need urgent results, tell your healthcare provider that you’re on your period. Labs can flag the sample and doctors can interpret the results with that context in mind. In some cases, a catheterized sample (collected directly from the bladder through a thin tube) bypasses vaginal contamination entirely, though this is typically reserved for situations where an accurate result is medically urgent.
For drug screenings, pre-employment tests, or pregnancy tests, there’s no reason to reschedule. These tests measure substances that menstrual blood doesn’t affect, and the presence of blood in the sample won’t invalidate the result or trigger a retest.
What to Tell Your Doctor or the Lab
Cleveland Clinic’s guidance is straightforward: let your provider know if you’re currently menstruating. This isn’t optional disclosure. It directly affects how your results are read. A lab that knows about your period can note it on the report, which tells the reviewing doctor not to chase down a false positive for blood or protein. Without that context, an abnormal-looking result could lead to unnecessary follow-up tests or a delayed diagnosis of the actual issue the test was meant to investigate.
If you get results back and realize you forgot to mention your period, contact your provider’s office. They can reinterpret the findings or schedule a repeat test. A single contaminated urinalysis isn’t a medical problem on its own, just a reason to collect another sample under better conditions.