Effient 10 mg & 162 mg asprin has lowered my dad's platelet count to 38k after 3 mon. Of angioplasty (1stent-lad). Should his doctor stop effient?

Probably. Low platelet count due to Effient is not common but bleeding risk is increased with platelet count at that level + efffient and aspirin. Usually drugs like Effient or Plavix (clopidogrel) are recommednded for one year for patients with drug eluting stents to help prevent clotting of the stent. Plavix (clopidogrel) may be less likely to cause low platelets. Talk to the doctor to understand the risk/benefit of the treatment.
He might have to, bu. He might have to, but it is risky, unless it was a bare metal stent. If it is a drug eluding stent, then it's a judgement call that only his cardiologist can make.