Blood test to find out why baby bites?????

[longagegap]

Hi just wondering if anyone else child has had this test.I cant remember what they called it , my son has global development dely and had bloods done yesterday the rest i know what they are for but the one for biting i dont know ,he is manic at doin this and wont use his hands for anything else but to bite them . He is 13 months , i know he is teething but this is all the time . He is due a visual brain test on Monday and an MRI scan on Thursday , if anyone knows the name of why the blood test is could u let me no please