Had a blood test done, and the doc said he had a low blood platelet count and will need to be retested. is that something serious?

Depends how: Low and if you have any other abnormalities in your blood work. Low platelets can cause delay in blood clotting. If you are not having any problems with bleeding, i would not worry too much. Follow your doctor's advice and have re-test first before you get too worried. Lab errors do occur. Isolated finding of low platelets could mean itp, a treatable disease.