A common cause of raised PSA is infection in prostate. Therefor your doctor has prescribed antibiotic and your PSA is in decreasing trend after treatment .
PSA is non specific test for detection of prostate cancer
. Although PSA level of 4 is taken as cutoff,no level of PSA can correctly predict whether a person has cancer or not.A person with PSA less than 4 has 15% risk of cancer, 4-10 have around 25% risk of cancer while >10 have around 67% risk.
If your PSA is persistantly high and/or there is some abnormal finding in your rectal examination
you can discuss with your doctor regarding biopsy-which is the only test that gives definitive diagnosis of cancer.