Microhematuria: Hematuria means blood in the urine and microhematuria refers to hematuria that is visible only under a microscope. There is so little blood that it cannot be seen without magnification.
Microhematuria is in contrast to gross hematuria in which the blood is so plentiful that it is visible grossly with merely the naked eye.
Hematuria, whether it be microscopic or gross, is abnormal and should be further investigated. It may or may not be accompanied by pain. Painful hematuria can be caused by a number of disorders, including infections and stones in the urinary tract. Painless hematuria can also be due to a large number of causes, including cancer.
The prefix "micro-" is derived from the Greek "mikros" meaning small. It diminishes whatever it precedes.