Hematuria is the presence of red blood cells in the urine. Visible hematuria, also known as gross hematuria (also frank hematuria or macroscopic hematuria), causes visible red or brown discoloration of the urine. Microscopic hematuria is invisible to the naked eye and is often found by urinalysis or urine dipstick; it is said to be chronic or persistent if 5 or more red blood cells (RBCs) per high-power field can be seen in 3 of 3 consecutive centrifuged specimens obtained at least 1 week apart. Any part of the kidneys or urinary tract (ureters, urinary bladder, prostate, and urethra) can leak blood into the urine. The causes of hematuria are broad, ranging from urinary tract infection to kidney stones to bladder cancer.
Microscopic hematuria is found regularly on routine urinalysis, with a prevalence between 0.18% and 37%. Some studies have shown increased incidence with age and female sex, but others did not show a correlation. In many people, no specific cause is found. Cancer of the kidney, prostate, bladder, or testes is found in 5% of people with microscopic hematuria and up to 40% of those with visible hematuria. Hematuria is common in pediatric populations, with a prevalence of 0.5–2%.
Certain substances can mimic hematuria either by discoloring the urine or by causing a false positive on urine dipstick. Causes of a false positive urine dipstick include hemoglobin (in absence of red blood cells), semen, myoglobin, porphyrins, betanin (after eating beets), and drugs (such as rifampicin, phenazopyridine, and sulphonamides). Substances that mimic hematuria by causing red or brown discoloration of the urine include drugs (such as sulfonamides, quinine, rifampin, phenytoin), betanin, and menses.