I heard that after cystoscope & ct scan for microscopic hematuria, 80% of time no cause is found and urine is monitored yearly. does that sound right?

Generally yes,: Before doing the imaging study and cystoscopy, a complete urinalysis should be done to evaluate for infection and the presence of red blood cell casts which would indicate glomerulonephritis. Also, a test for calcium/creatinine ration for evaluation of hyper calciuria, a common cause of hematuria. Sometimes checking other close family members is helpful, as there is a familial hematuria syndrome