How is maple syrup urine disease diagnosed?

Newborn screen: In the US, MSUD is part of the newborn screen all babies get before leaving the hospital, but it's usually symptomatic in the first weeks after birth when amino acids start to accumulate in the blood. Symptoms are poor feeding, irritability, seizures, and smelly urine. Definitive test is quantitative plasma amino acids, and is usually done on day of life 2 if there is a family history of MSUD.