Does prolonged menstrual bleeding affect urine test results?

Under normal circumstances, having an ongoing menstrual period can affect urine test results, potentially causing abnormalities that interfere with a doctor's assessment. Therefore, routine urinalysis is not recommended during this time. The detailed explanation is as follows:

When menstruation has not completely finished, small amounts of menstrual blood may continue to discharge from the vagina. During a routine urinalysis, this blood may mix into the urine sample. Menstrual blood contains components such as red blood cells, white blood cells, and endometrial tissue, which can lead to elevated red blood cell counts in the urine. It may also affect the detection results of other indicators such as white blood cells and protein, thus failing to reflect the true condition of the urine.

The extent of this interference varies among different urinalysis parameters. The most significant impact is on red and white blood cell measurements in routine urine tests, while metabolic indicators such as glucose and ketones are less affected. However, sample contamination may still render overall results unreliable.

If a urine test is absolutely necessary during an ongoing menstrual period due to special circumstances, it is important to clean the external genitalia with warm water beforehand to prevent menstrual blood from contaminating the sample. Collecting a midstream urine specimen can help minimize contamination as much as possible. For routine urinalysis, it is best to avoid the menstrual period itself as well as the three days before and after menstruation, waiting until menstrual bleeding has completely stopped to ensure accurate test results.