Histologically proven AMA positive primary biliary cholangitis but normal serum alkaline phosphatase: Is alkaline phosphatase truly a surrogate marker?

BACKGROUND AND AIMS

The most highly directed and specific autoantibody in human immunopathology is the serologic hallmark of primary biliary cholangitis (PBC), antimitochondrial antibodies (AMAs). However the clinical significance of finding a positive AMA, with normal alkaline phosphatase (ALP) remains enigmatic.

METHODS

We took advantage of 169 consecutive outpatients who were identified as having a positive AMA, but normal ALP levels between January 2012 and January 2018. A liver biopsy was performed on 67/169 of these AMA positive normal ALP patients.

RESULTS

In all 169 patients we reconfirmed the AMA and also performed anti-gp210 and anti-sp100, liver stiffness (LSM) assessed by vibration-controlled transient elastography (VCTE), an abdominal computed tomography (CT) scan, and either a magnetic resonance imaging (MRI) or ultrasound. The liver biopsies were reviewed by two unbiased observers. 87.6% of the 169 patients were females with a mean age of 46; the median AMA titer 1:320; an elevated serum IgM was found in 53.3%. Importantly, in patients with a liver biopsy, 55（82.1%）out of 67 had varying degrees of cholangitis activity, diagnostic of PBC.

CONCLUSION

In patients who were AMA-positive but had normal ALP levels, more than 80% were associated with histological classic PBC. These data emphasize the importance of a positive AMA, even with a normal ALP and also question the role of ALP as a sole surrogate marker of cholangitis.