The most valuable ancillary tests for the diagnosis of hepatic coma include blood ammonia measurement, electroencephalogram, evoked potentials examination, cranial CT or MRI. Hepatic coma, also called hepatic encephalopathy, is a metabolic disorder caused by severe liver disease, resulting in dysfunction of the central nervous system. Blood ammonia measurement checks the amount of ammonia in the blood. Elevated blood ammonia helps diagnose chronic hepatic encephalopathy, but blood ammonia can be normal in patients with acute hepatic encephalopathy. Electroencephalogram (EEG) can detect the electrical activity of brain cells, and in hepatic coma, high amplitude delta waves may be seen, but they are of less value in the diagnosis of subclinical hepatic encephalopathy. Evoked potential examination can be used to diagnose mild hepatic encephalopathy, and the evoked potential latency can be prolonged. Examinations such as cranial CT or MRI can detect signs of cerebral edema and cerebral atrophy, which can help diagnose acute hepatic encephalopathy and chronic hepatic encephalopathy. Other organic lesions of the cranium can also be detected to help in differential diagnosis. When hepatic coma occurs, it is recommended to seek timely medical treatment and standardize the treatment under the guidance of professional doctors.