Do anti-smooth muscle antibodies predict development of autoimmune hepatitis in patients with normal liver function? – A retrospective cohort review

BackgroundThe presence of anti-smooth muscle autoantibody (SMA) in Autoimmune Hepatitis (AIH) is well established. However, there are no data demonstrating the clinical significance in patients with normal liver function and few showing positive predictive value for AIH when alanine aminotransferase (ALT) is raised.MethodsWe retrospectively established outcomes in a cohort of 251 consecutive patients with positive tubular or glomerular SMA. Patient records were checked for 12 years after the positive SMA result to identify development of AIH.ResultsOf 202 patients with SMA and ALT < 55 IU/L, one (0.5%) had a subsequent diagnosis of AIH and this patient probably had abnormal ALT at the time of SMA detection. 22% of 45 patients with raised ALT (> 55 IU/L) and 23% of 43 patients with persistently raised ALT (> 3 months duration), had a diagnosis of AIH on follow up. Of 10 patients with AIH, 80% were diagnosed within three months of the positive SMA.ConclusionsProgression to AIH in patients with normal liver function and positive SMA-T/G is rare but patients with positive SMA and raised ALT (> 55 IU/L) should be referred to secondary care for investigation. Positive predictive value of SMA with raised ALT for AIH was 22%.