How does menstrual blood affect Leukocyte Esterase (LE) results in urinalysis?

From the Guidelines

The presence of menstrual blood in urine can cause false positive leukocyte esterase results on a urinalysis, and to obtain accurate results, it's recommended to avoid collecting urine samples during menstruation if possible. This occurs because red blood cells from menstruation can interfere with the chemical reaction used to detect leukocyte esterase, which is an enzyme produced by white blood cells. When menstrual blood contaminates a urine sample, the test strip may detect the presence of white blood cells that are actually from the menstrual blood rather than from a urinary tract infection.

Key Considerations

• Menstrual fluid contains not only red blood cells but also white blood cells and other cellular components that can trigger the leukocyte esterase reaction 1.
• To minimize contamination, a clean-catch midstream urine collection technique should be used, and the healthcare provider should be informed about the menstruation to properly interpret the results.
• In some cases, alternative testing methods like urine culture may be needed to confirm or rule out a urinary tract infection when menstrual contamination is suspected.

Clinical Implications

• Healthcare providers should be aware of the potential for false positive results when interpreting urinalysis results from patients who are menstruating.
• If infection is suspected based on urinalysis or symptoms, a urine culture should be obtained; if infection is confirmed, the evaluation should be repeated after treatment to document resolution of hematuria 1.
• Given the potential intermittent nature of hematuria, some organizations specifically recommend up to 3 repeated analyses in these scenarios, and providers may consider repeated microscopic testing on the basis of the risk associated with the clinical presentation 1.

From the Research

Effect of Red Color from Menstruation on Leukocyte Esterase Results

• There are no direct studies that investigate the effect of the red color from menstruation on leukocyte esterase results of a urinalysis 2, 3, 4, 5, 6.
• However, it is known that leukocyte esterase is an enzyme produced by white blood cells, and its presence in urine can indicate a urinary tract infection (UTI) 5.
• The sensitivity and specificity of a urine leukocyte esterase dipstick test for the diagnosis of UTI have been studied, with results showing a sensitivity of 63.6% and a specificity of 44.2% 5.
• Microfluidic paper-based devices have been developed for the quantitative detection of leukocyte esterase in urine, with a detectable range of 2 to 32 U mL-1 6.
• The presence of blood in urine, such as during menstruation, may potentially interfere with the results of a urinalysis, including the leukocyte esterase test 2, 3.
• However, without direct evidence, it is unclear how the red color from menstruation specifically affects the leukocyte esterase results of a urinalysis 2, 3, 4, 5, 6.

Urine Sample Collection and Contamination

• The method of urine sample collection can affect the results of a urinalysis, with midstream clean-catch samples often recommended to minimize contamination 2, 3.
• However, studies have shown that the contamination rates of midstream clean-catch samples are not significantly different from those of other collection methods 2, 3.
• The use of a vaginal tampon during urine sample collection has been studied as a method to decrease contamination from the vagina, but results have shown no significant difference in contamination rates 3.

Diagnostic Accuracy of Urine Cultures

• Urine cultures are considered the gold standard for diagnosing UTIs, but the results can be affected by contamination and other factors 2, 3, 4.
• The diagnostic accuracy of urine cultures has been studied, with results showing that the sensitivity and specificity of urine cultures can vary depending on the population and collection method 2, 3, 4.