Complete blockage of the urethra (acute urinary retention, or AUR). This results in a complete inability to urinate. It can cause kidney damage, which may be reversed if the problem is diagnosed and treated before the damage becomes too severe.
Long-term, partial blockage of urine flow from the bladder (chronic urinary retention, or CUR). This causes urine to remain in the bladder after urination (post-void residual urine).
A urinary tract infection (UTI). But repeated urinary tract infections can also be caused by long-term inflammation or infection in the prostate (chronic prostatitis).