Improving the accuracy of clinical interpretation of serological testing for the diagnosis of acute hepatitis a infection

Background: Hepatitis A (HA) remains a common infection globally that results in a self-limiting hepatitis with gastrointestinal and systemic symptoms. Direct detection of the virus in blood or stool is often not possible once symptomatic. Serological testing is frequently performed to investigate abnormal liver function tests - and interpretation of equivocal and low-level positive anti-hepatitis A virus (HAV) IgM is difficult even in the context of accurate epidemiological and clinical information. Objectives: The aim of this project was to characterise the association between low-level reactive anti-HAV IgM results and clinical disease. Study design: Anti-HAV serology results recorded over 22 months were analysed. Equivocal and positive Architect anti-HAV IgM results were matched with available clinical and demographical data to identify confirmed and probable cases of acute HAV infection. Results: Reactive anti-HAV IgM results were recorded for 88/7661 (1.15%) samples. Using clinical and laboratory data, 35 patients were confirmed to have acute HAV infection. Acute HA was associated with a mean Architect anti-HAV IgM value of 9.4 (SD 6.8-12.0). Cases of HA had a mean peak ALT value of 1920 (SD 682-3158). All confirmed cases (35/35) of acute HAV were associated with at least one clinical indicator, with 28/31 cases (90%) having a documented jaundice. All 35 (100%) cases of acute HAV infection had anti-HAV IgM > 4.0. A diagnosis other than acute HA was identified in 7/11 (63.6%) of low-level reactive anti-HAV IgM results (clinical data unavailable for further 4/11, 36.3%). Where clinical information was available, acute HA was excluded in all 31 patients with equivocal or low-level reactive anti-HAV IgM results. Conclusions: The accuracy of reports sent out to the clinician showed room for improvement. An interpretive algorithm is proposed including a clinically significant cut-off value for anti-HAV IgM.