“Hepatitis b?”

The only sure way is to compare the date of a + test against the date of any prior - test. Otherwise, you can glean the date from clinical symptoms of hepatitis(whcih can be very subtle or even asymptomatic)--like fatigue, weight loss, jaundice, dark urine, pale stools, etc, etc. Lastly, a hepatitis IgM antibody blood test result may help determine when it occurred. And a doctor will put all of these together to come up with a possible date--knowing that it may not be possible to do so with any certainty.