All the patients suspected of viral hepatitis are tested for hepatitis viruses A, B and C: IgM anti-HAV, HBsAg, IgM anti-HBc, anti-HCV. If any of these markers are positive, there are conducted further serological tests to differentiate acute infection from chronic infection or past infection. If there is confirmed the presence of hepatitis B virus, anti-HDV (antibody to hepatitis D virus) is measured.
Tests for IgM anti-HEV (IgM antibody to hepatitis E virus) are measured if the patient is (or have recently traveled to) an endemic area and if the test is available.
In uncertain cases HCV-RNA and HBV-DNA can be measured, although these are sophisticated tests and are not routinely available.

At its onset, acute hepatitis mimics various non-specific diseases. Usually, hepatitis is suspected only when jaundice develops. At this stage hepatitis should be differentiated from other disorders associated with jaundice.
Hepatitis diagnosis includes non-specific liver function tests: aminotransferases (ALT and AST), bilirubin, alkaline phosfatase, etc. AST and ALT are usually highly elevated in hepatitis (> 400 IU/L) and ALT is usually higher than AST. The level of aminotransferases not always correlates with clinical severity of hepatitis, which means that ALT and AST can be markedly increased, but the evolution of hepatitis can be relatively mild, and vice versa.
Hyperbilirubinemia can be variable in hepatitis and usually is preceded by urinary bilirubin (darkening of urine). Alkaline phosphatase is moderately elevated in hepatitis.
If viral hepatitis is suspected, it is necessary to effectuate serological studies, to determine the type of virus.