Biomarker: RBC, urine

Overview

Urine RBC measures the number of red blood cells present in a urine sample, usually reported as red blood cells per high-power field (RBC/HPF) on microscopic examination. Red blood cells normally remain within the bloodstream, so increased urinary RBCs may indicate bleeding or inflammation anywhere in the kidneys or urinary tract. Potential causes include urinary tract infection, kidney stones, kidney inflammation or injury, prostate disease, and urinary tract cancers. The measurement is clinically useful for detecting and evaluating hematuria, including microscopic hematuria that is not visible to the naked eye.

Clinical Use Cases

Detecting microscopic or visible hematuria.
Evaluating possible urinary tract infection, kidney stones, kidney injury, or urinary tract inflammation.
Supporting assessment of glomerular kidney disease when dysmorphic RBCs or RBC casts are present.
Investigating possible prostate, bladder, kidney, or other urinary tract disease.
Confirming a positive urine dipstick blood result, because dipstick testing alone does not establish microscopic hematuria.
Monitoring hematuria or urinary abnormalities during clinical evaluation or follow-up.

Specimen Types

Midstream, clean-catch urine specimen.
Random urine specimen.
First-morning urine specimen when specifically requested.
Urine sediment obtained after centrifugation for microscopic examination.
Timed or 24-hour urine collection when ordered for broader urinary testing.

Measurement Methods

Manual urine sediment microscopy with bright-field or phase-contrast microscopy.
Automated urine particle analysis using flow cytometry or digital imaging systems.
Urine reagent-strip testing for heme as an initial screening method. This detects heme activity and does not directly count intact RBCs, so positive results should be confirmed by microscopy.
Morphologic assessment of RBCs, including evaluation for dysmorphic RBCs and RBC casts when glomerular bleeding is suspected.

Test Preparation and Influencing Factors

No fasting is usually required for an isolated urine RBC test.
Use the clean-catch technique to reduce contamination from skin, genital secretions, or external blood.
Menstrual blood or bleeding hemorrhoids can contaminate the specimen and cause an inaccurately high result; inform the health care professional before collection.
Excessive fluid intake may dilute urine and affect some urinalysis results.
Vigorous exercise can temporarily cause hematuria in some individuals.
Tell the health care professional about prescription medicines, over-the-counter medicines, vitamins, and supplements. Do not stop medicines unless instructed.
Some medicines and foods can change urine color and may resemble visible blood without indicating RBCs in the urine.
Analyze the specimen promptly because urinary cells can deteriorate during storage, potentially reducing the measured RBC count.
A positive dipstick blood result should be evaluated with microscopic urinalysis rather than interpreted as urine RBC elevation by itself.