My 5 week old was dx with entrovirus. he also had a positive lactoferrin stool culture. his ammonia level was 80. could this be a metabolic disorder?

Unlikely: A severe infection such as adenovirus before the immune system has matured at about 2 mo. puts a great strain on the body's metabolism, likely sufficient to raise the ammonia level. It most likely will disappear as he recovers. The lactoferrin just indicates that he had significant inflammation of his intestines from the adenovirus. Urine for organic acids is a good metabolic screening test.