‘True’ antimitochondrial antibody-negative primary biliary cirrhosis, low sensitivity of the routine assays, or both?

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Abstract
Anti‐mitochondrial antibody (AMA) is considered the serological hallmark of primary biliary cirrhosis (PBC), but may be missing in a proportion of these patients. We assessed sensitivity and specificity of the currently available techniques for AMA detection in a large series of PBC patients and controls, and analysed their clinical and immunological features according to the AMA status. By indirect immunofluorescence on rat tissue sections and HEp‐2 cells, Western immunoblot with bovine submitochondrial particles, and two ELISAs with AMA‐specific recombinant proteins, we evaluated the presence of AMA in 127 PBC patients, 166 patients with type 1 autoimmune hepatitis and 100 with non alcoholic fatty liver disease. In PBC patients Western immunoblot detects AMA significantly more often than indirect immunofluorescence on HEp‐2 cells (85%versus 72%, P = 0·02) or rodent tissue sections (71%, P = 0·01); both ELISAs are only slightly less sensitive than Western immunoblot (81% and 78%). Ten patients with non alcoholic fatty liver disease were AMA‐positive by indirect immunofluorescence, but none recognized AMA‐specific epitopes in Western immunoblot or in ELISAs. Twelve patients with type 1 autoimmune hepatitis were AMA‐positive by indirect immunofluorescence, but only 6 (3·6%) reacted by Western immunoblot and ELISAs. Western immunoblot or ELISA should be regarded as first‐line assay for the detection of AMA. Up to 15% of PBC patients are consistently AMA‐negative, yet they share the same clinical, biochemical and histological features of AMA‐positive PBC. Detection of AMA in type 1 autoimmune hepatitis might identify a subset of patients at risk of developing a hepatitic/cholestatic syndrome.

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