A father says Fiona Stanley Hospital medical staff failed to conduct a simple test that would have prevented his son dying from a drug they prescribed.

Philip Olsen says his son Jared was originally admitted to Fiona Stanley Hospital for further treatment of severe stomach pains which was diagnosed as probable Chrones disease in Feburary.

Mr Olsen told Gary Adshead his son was discharged with a number of medications including the drug Mercaptopurine.

Mr Olsen says a standard blood test was not conducted to see if Jared would be safe to take the drug.

Jared died on the 5th of March from body toxicity reaction from the drug.