Do I need to have blood test before taking Finasteride?

In my opinion,  finasteride lowers the PSA by approximately 50%.. I recommend that you get a baseline PSA  and follow the recommendations of your urologist for follow up testing and examination.

No.  I generally prescribe the drug without a blood test.  The diagnosis is clinical and most men, especially those with recent onset of androgenic alopecia, respond well to the drug.

I recommend you get a baseline PSA with your urologist before starting Finasteride.  Make sure you follow up with your urologist.  Finasteride can also cause sexual side effects.  Always seek treatment from a qualified physician.