What does it mean in my last urinalysis : positive rbc 1-5, the reference range for it in lab is ...negative per hpf ;?

The only thing to: Surmise from this information is that you have 1-5 rbc's presumably per high powered field which is micro-hematuria. Without any other information that is all that can be deduced.

Probably nothing: Many labs consider this within "normal limits." one common standard for microhematuria is 3 or more red cells on 2 of 3 properly-collected specimens. I trust there were no other abnormalities, especially no red cell casts. Anything from subtle kidney disease to a bouncy ride on a bicycle to see the doctor can be the explanation.