Abstract: Background–Abnormal bile acid (BA) metabolism has been observed in dogs with chronic enteropathy (CE). In humans, BA malabsorption (BAM) results in excessive BA loss into the colon, triggering secretory diarrhea. This leads to compensatory BA synthesis from cholesterol. Serum 7α-hydroxy-4-cholesten-3-one (C4), a key marker for the rate of BA synthesis, serves as a marker for BAM in humans. However, studies in dogs are limited.Objectives–To develop and analytically validate a liquid chromatography with tandem mass spectrometry (LC-MS/MS) method to quantify C4 in dog serum. Animals–17 privately-owned healthy control dogs (HC) and 15 dogs with CE with partial or no response to food and immunosuppressant trials. Methods–A cross-sectional retrospective study. The LC-MS/MS was validated according to FDA guidelines for bioanalytical method validation. Serum C4 quantification was performed using 50 µL of serum samples through LC-MS/MS. Serum C4 concentrations were compared between groups by Mann-Whitney U-test.Results–The assay was analytically validated with good linearity (1-1000 ng/mL, R = .999) and adequate coefficients of variation of inter-assay (median: 1.4%, range: 4.2-7.9) and intra-assay (median: 12.1%, range: 7.4-14.8). Dogs with CE had significantly (p = .009) higher serum C4 concentrations (median: 53, range: 20-204 ng/mL) than HC (median: 26, range: 16-44).Conclusions and Clinical Importance–Increased serum C4 concentrations were found in a subset of dogs with CE that poorly responded to standard treatments, suggesting a compensatory hepatic BA synthesis. This aligns with previous findings of decreased BA transporters in the ileum of dogs with CE and increased fecal BA concentrations.
