How To Treat High Potassium Level With Down Syndrome Condition?

Hi,I have received a call from our new GP today in regards to a recent annual blood test my 9 year old son Ashton has had. Ashton has Down Syndrome and the new bloods are showing a high potassium level. Can you tell me if this is another common thing for people with Down Syndrome or just one of those things. Ashton had open heart at age 3 to repair a 30mm ASD and has had no heart problems since.Thanks for your time Meaghan