Should I have biopsy with PDA of 3.5?

Depends! I suspect you're referring to psa (prostate specific antigen) rather than pda. We typically consider levels <4 to be normal but we also know that normal varies w/age (higher being accepted w/aging). Psa also increases w/infection. Steady increases in psa (even if <4) warrant further evaluation, eg biopsy. But a steady value or an initial value <4 probably can be watched. Talk w/your family doc.