From the Guidelines
Menstrual blood in urine can significantly affect urinalysis results, potentially leading to false positive findings, and it is recommended to collect urine samples outside of the menstrual period when possible to avoid interference 1. When menstrual blood contaminates a urine sample, it can cause the appearance of red blood cells, protein, and hemoglobin in the urinalysis, mimicking conditions like urinary tract infections or kidney disease when none are present. To minimize contamination, the following steps can be taken:
- Using a tampon before collection
- Collecting a midstream sample after thorough cleansing of the genital area Alternatively, a catheterized specimen may be necessary for accurate results in urgent situations, as suggested by the American Urological Association's best practice policy recommendations 1. This interference occurs because menstrual blood contains the same components that would be abnormal if originating from the urinary tract itself, making it difficult for standard urinalysis to distinguish between menstrual contamination and true urinary pathology, highlighting the importance of careful patient history and physical examination to exclude local causes of microscopic hematuria 1. In cases where hematuria is suspected to be caused by menstruation, repeat urinalysis 48 hours after cessation of menstruation can help confirm the diagnosis, and no additional evaluation is warranted if the hematuria has resolved 1.
From the Research
Urinalysis and Menstruation
- The effect of menstrual blood on urinalysis results is not directly addressed in the provided studies 2, 3, 4, 5, 6.
- However, study 2 mentions that the differences between midstream clean-catch and catheterization urinalyses do not appear to be significant in the majority of ambulatory women without active vaginal bleeding who present with symptoms suggestive of a urinary tract infection.
- This implies that the presence of menstrual blood may affect the results of urinalysis, but the study does not provide further information on this topic.
Menstrual Cycle and Urinary Symptoms
- Study 6 investigates the impact of the menstrual cycle on urinary symptoms and the results of urodynamic investigation.
- The study finds that 41% of women reported cyclical urinary symptoms, with the majority experiencing worsening symptoms just before or during their period.
- The prevalence of abnormal detrusor activity on videocystourethrography increased significantly with time from the last menstrual period, which may be related to increases in circulating progesterone levels 6.
Uroflowmetry and Menstrual Cycle
- Study 5 compares bladder emptying function in normal women during the proliferative and secretory phases of the menstrual cycle.
- The study finds that uroflowmetry parameters were not significantly different between the two phases of the menstrual cycle, suggesting that the menstrual cycle does not have a significant impact on uroflowmetry results 5.