GPT and hepatitis A virus infection: To illustrate this consider two patients; a patient with an acute hepatitis A infection can have ALT values >1000 U/L, whereas a patient with hepatitis C can have an ALT within the normal reference interval, yet 10 years later the patient with hepatitis A is likely to be alive and well irrespective of how they are managed, whereas the patient with hepatitis C if not investigated and diagnosed is at substantial risk of progressing to end-stage liver disease.