3yo with autism has high TSH and normal free T4

My son had some blood tests and here are the results. 

                                           Ref ranges

TSH - 8.1                        0.27-4.5

Free T4- 15.2.                 11-23

Is this anything to be concerned about? I have read there are links between autism and the thyroid. 

That is a high TSH, indicating hypothyroidism. What does the Doctor Say?

The doctor hasn't said anything. This blood test was from months ago when they were checking for fragile x. We were told there were no issues. 

Only this week when my wife was with the dietician did she see these tests apppear on the screen and asked for a copy. 

TSH was well outside the normal ranges which prompted me to post on this site. I would have thought the doctors would have spotted it months ago when the bloods were taken. 

He is out of range on a few others but TSH was very high?

Should I go to GP about this? What follow up tests should I mention?

Certainly see the Doc and ask for another test.