Wikipedia
Microhematuria
Microscopic hematuria is a medical condition in which urine contains small amounts of blood. Blood quantity is too low to change the color of the urine (otherwise, it is known as gross hematuria). While not dangerous in itself, it maybe a symptom of kidney disease, such as IgA nephropathy, which should be monitored by a doctor.
The American Urological Association (AUA) recommends a definition of microscopic hematuria as three or more red blood cells per high-power microscopic field in urinary sediment from two of three properly collected urinalysis specimens.