Science of Urinalysis - What is Hematuria

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What is Hematuria

Hematuria is defined as the presence of blood in urine, specifically red blood cells. Hematuria can be classified as gross which means the blood is visible to the eye, or microscopic when the blood cannot be seen and is only detected during testing, either through a chemical reaction, utilizing flow cytometry or under a microscope.

Hematuria can be caused by many factors. Often, it is associated with infections in the urinary tract or, less commonly, it may be due to kidney disease or even cancer in the kidney, bladder or prostate. Gross or microscopic hematuria can also accompany bladder and kidney stones. There are also certain medications that can cause hematuria.

When testing urine, laboratorians need to be aware of how to handle grossly bloody urine samples as well as the possibility of interference on the blood pad of urine dipsticks. Grossly bloody urine that is red, purplish or brown may interfere with results from automated urine dipstick readers; it may be necessary to manually read the results, noting how the color of the reaction pads change throughout each parameters’ stated reaction period. Microscopic hematuria should also be handled with care. High concentrations of ascorbic acid or a urine pH <5.1 are known to cause false-negative blood results on urine dipstick; a false-positive result for blood may be caused by hemoglobinuria, myoglobinuria, some soaps and detergents (including bleach) and certain bacteria. Because interference on the blood pad is not uncommon, it is important to correlate the dipstick results with the microscopic findings.

Resources:

Delanghe J, Speeckaert M. Preanalytical requirements of urinalysis. Biochem Med (Zagreb). 2014 Feb 15;24(1):89-104. doi: 10.11613/ BM.2014.011. PMID: 24627718; PMCID: PMC3936984.

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