Worried about my dad

Hi!


Hoping you can help a concerned daughter 

My dad, he is 71.. and recently at his annual GP check his blood work found possibly something wrong with his kidney. He was sent for an ultrasound and a urine sample was taken. 
The urine sample was normal but the ultra sound found he has an enlarged prostate. 
He has now been asked to have a PSA test.. all communication with the GP is over text and we have no idea why this test had been ordered when an enlarged prostate is a benign condition. 
does the GP always order a PSA test after finding this condition or are they looking for cancer. 

Any help or advice would be amazing