Microhematuria , also called microscopic hematuria (both usually abbreviated as MH ), is a medical condition in which urine contains small amounts of blood ; the 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 may be a symptom of kidney disease, such as IgA nephropathy or Sickle cell trait ,  which should be monitored by a doctor.
“Microscopic” means something is so small that it can only be seen through a special tool called a microscope. “Hematuria” means blood in the urine. So, if you have microscopic hematuria, you have red blood cells in your urine. These blood cells are so small, though, that you can’t see the blood when you urinate.