[Differential characteristics of AMA-M2 autoantibody in primary biliary cirrhosis and non-PBC patients].

Objective To explore the differential characteristics of the AMA-M2 autoantibody in patients with primary biliary cirrhosis (PBC) and non-PBC patients. Methods Patients with abnormal liver function at the Capital Medical University affiliated to Beijing You-an Hospital were enrolled in this study between January 2011 and December 2013. Serum levels of ANA, AMA and AMA-M2 were detected by indirect fluorescence assay and enzyme-linked immunosorbent assay. The patients' clinical data was obtained for retrospective analysis. Statistical analyses were performed using the SPSS 16.0 software. Enumeration data have been presented as numbers and percentages, and were analyzed using the chi-square test and one-way ANOVA test. Results Of the 5315 patients with abnormal liver function, 15.3% (811/5315) were AMA-M2 positive patients; among those 811 patients, 78.4% (636) had PBC, 4.4% (36) had PBC overlapping with autoimmune hepatitis (AIH), 4.4% (36) had drug-induced liver injury, 6.5% (53) had hepatitis B, 3.3% (27) had hepatitis C, 0.6% (5) had hepatitis E, 0.9% (7) had alcoholic liver disease, 0.5% (4) had non-alcoholic fatty liver, 0.8% (6) had primary hepatic carcinoma, and 0.1% (1) had infectious mononucleosis. Serum AMA-M2 level was significantly higher in the PBC patients (vs. other groups, p < 0.001) with the exception of the patients with PBC/AIH overlap syndrome. Among the 811 patients with AMA-M2 positivity, 88.5% (718) showed AMA positivity and 91.1% (739) showed ANA positivity. Serum alanine transferase (ALT) and aspartate transferase (AST) levels were significantly higher in the drug-induced liver injury patients (527.74±684.65 U/L, 490.60±716.89 U/L) and the hepatitis E patients (1015.94±165.55 U/L, 665.4±297.14 U/L) than in the PBC patients (96.02±115.56 U/L, 94.82±83.32 U/L) (ALT:F = 8.041, p < 0.001, p < 0.001; AST:F = 8.066, p < 0.001, p < 0.001). Serum alkaline phosphatase (ALP; 265.16±179.08 U/L) and glutamyl transferase (GGT; 332.02±279.29 U/L) were significantly higher in the PBC patients than in the hepatitis B patients (135.35±123.17 U/L, 140.27±229.24 U/L) and the hepatitis C patients (85.65±27.77 U/L, 92.70±125.72 U/L) (ALP:F = 3.911, p = 0.01, p = 0.001; GGT:F = 4.081, p < 0.001, p < 0.001).The serum IgM level was significantly higher in the PBC patients (4.60±2.67 g/L) than in the patients with drug-induced liver injury (1.76±1.15 g/L), hepatitis B (2.02±1.41 g/L), hepatitis C (1.48±0.92 g/L), hepatitis E (1.40±0.68 g/L),alcoholic liver disease (1.57±1.07 g/L), non-alcoholic fatty liver (1.05±0.72 g/L), and primary hepatic carcinoma (2.64±2.26 g/L)(F = 16.83, p < 0.001, p < 0.001, p < 0.001, p < 0.05, p < 0.01, p < 0.05 respectively). Conclusions Although detection of serum AMA-M2 is an important feature of PBC diagnostic testing, there is a high ratio of serum AMA-M2 detected in patients with drug-induced liver injury, hepatitis B, C and E, alcoholic liver disease, non-alcoholic fatty liver, and primary hepatic carcinoma. The AMA-M2 positive non-PBC patients still require close observation to watch for future development of PBC. Key words: Liver diseases; Antibodies, antinuclear; Non-primary biliary cirrhosis; Antimitochondrial antibody M2 subtype