You may want to check out this article on health screening in Singapore here.
As pointed out by Dr Hwee Yong, there are many causes for an elevated PSA test, so the doctor must interpret these findings on the background of asking questions related to your history (eg. any urinary symptoms? Any weight loss? Any blood in your urine? etc), as well performing a proper clinical examination (in this case, a prostate examination).
As a next step, I’d suggest seeing either a GP at a private or polyclinic. He will be able to advise you on the follow-up after determining the answers to the above.
Cheers
