Recently, we have had three patients who had weak positive ('grayzone') hepatitis B surface antigen results due to administration of the hepatitis B vaccine within 5 days of the laboratory test.  This has been an intermittent but steady occurrence over the last several years.  Historically, this happens most commonly when a patient receives the vaccine on a different patient encounter than the laboratory testing.

The hepatitis B vaccine contains surface antigen, which is detectable by the hepatitis B surface antigen assay and can cause either grayzone or positive results, with positive results reported to Iowa Department of Public Health.  Positive (as opposed to grayzone) results are more common in children where the amount of surface antigen in the vaccine is higher relative to body weight than in adults.  As a general guideline, please avoid testing for hepatitis B surface antigen within 5 days of a patient having received the hepatitis B vaccine.  This will avoid false positives.

Questions should be directed to Matthew Krasowski, MD, PhD, Medical Director of the Clinical Chemistry Laboratory (384-9380, matthew-krasowski@uiowa.edu).