Inter- and Intra-individual Variation, and Limited Prognostic Utility, of Serum Alkaline Phosphatase in a Trial of Patients With Primary Sclerosing Cholangitis

Abstract

Background & aims: Serum alkaline phosphatase (ALP) and the enhanced liver fibrosis (ELF) score are used as endpoints in trials of patients with primary sclerosing cholangitis (PSC). We aimed to quantify inter- and intra-individual variation in levels of ALP and the ELF score over time, and evaluated their association with fibrosis progression.

Methods: We analyzed data from 234 patients with large-duct PSC enrolled in a 2-year, phase 2b placebo-controlled trial of simtuzumab. Participants were assessed by laboratory tests every 4 weeks, and liver biopsies collected at time of screening, week 48, and week 96.

Results: Serum levels of ALP and ELF scores did not differ significantly between simtuzumab and placebo groups, so the data were pooled. Median per-patient variations in ALP between clinic visits were approximately 12% over 12 weeks, 20% over 48 weeks, and 20% over 96 weeks. Reductions, unrelated to study intervention, of more than 40% in ALP were observed in 10.9% of patients with baseline activity greater than 2-fold the upper limit of normal (ULN) and 12.5% of patients with more than 3-fold the ULN at 1 year. At 2 years, reductions of more than 40% in ALP were observed in 15.8% of patients with baseline activity greater than 2-fold the ULN and 17.9% of patients with more than 3-fold the ULN. Among the 209 patients with Ishak fibrosis stage 0-4 at baseline, serum ALP activity did not associate with development of cirrhosis or with a 2-point increase in fibrosis stage at 2 years. In contrast, the median per-patient variation in ELF scores between clinic visits was approximately 3% over 12 weeks, 4% over 48 weeks, and 4% over 96 weeks. Elevated ELF scores at baseline and at weeks 12, 24 and 48, each associated with development of cirrhosis at 2 years (odds ratio >2.75; P < .01 for all timepoints). ELF scores at baseline and weeks 12, 24 and 48, also associated with a 2-point increase in fibrosis stage at 2 years (odds ratios all greater than 2; P < .01 for all timepoints).

Conclusions: In an analysis of data from patients with large-duct PSC enrolled in a prospective trial, we found large interindividual and intraindividual variations in serum ALP activity. Serum ALP activity did not associate with disease progression over a 2-year period. Variations in ELF score were smaller, and scores determined at multiple timepoints associated with fibrosis progression and development of cirrhosis.

Keywords: Biomarker; Cholestasis; Immune-Mediated Liver Disease; Prognostic Factor.