We describe a case of Argininemia detected by Michigan Newborn Screening (NBS). The Secretary's Advisory Committee on Heritable Disorders in Newborns and Children recommends that every MS/MS newborn screening program include Argininemia as part of their uniform screening panel. While affected infants will be detected by this testing, Arginine levels may take time to accumulate. Thus, some infants may not be detected by this methodology and early sample collection. In Michigan, since initiating testing for Argininemia in 2006, there has been workup of 23 cases for elevated Arginine identified by NBS, with one case identified as affected. We report this affected case. Subsequently, the Arginine/Ornithine ratio was calculated for all cases and was found to be informative with respect to predicting whether a patient is affected by Argininemia.