Embodiments of the present invention are directed to a biological marker, the gamma isoform of protein kinase C (PKCg), which surprisingly allows rapid identification of compromised cognitive, behavioral, and neuropsychological functions under conditions associated with acute, transient hypoxia in humans. It was surprisingly discovered that PKCg is released from neural cells and can be detected in peripheral blood after hypoxic events unrelated to the reduction or elimination of blood flow through affected tissues. Embodiments of this invention are also directed to a broad range of clinical applications, particularly in emergency medicine. Other embodiments are related to compositions and methods for distinguishing between hypoxic encephalopathies and conditions arising from neuroanatomical/structural anomalies and/or incidental pathologies, for example, alcohol intoxication.