New Blood-Based Test, 7-Alpha-Hydroxy-4-Cholesten-3-One (7AlphaC4), for Bile Acid Malabsorption in Patients With Inflammatory Bowel Disease or Unspecified Diarrhea

Background: Serum 7AlphaC4 is a diagnostic test for bile acid (BA) malabsorption (BAM) or bile acid diarrhea (BAD) and the only available blood-based test for BAM/BAD. Elevated concentrations (>57 ng/mL) are associated with excess colonic bile acids as the cause of diarrhea. Concentrations >48 ng/mL may have a high positive predictive value (PPV) of 82% for bile acid diarrhea and high likelihood of responding to BA sequestrants. As a BA precursor, 7AlphaC4 is an intermediate in BA biosynthesis from cholesterol. In BAM, less BAs re-enter enterohepatic circulation and more BAs spill into the colon where they increase motility and secretion. At the same time, less reabsorbed BAs means less negative feedback and an ensuing increase in hepatic BA synthesis. As BA synthesis increases, blood levels of 7AlphaC4 also increase. Thus, 7AlphaC4 is a surrogate measure of stool BA that obviates the need for a nuclear medicine test or stool collection. Methods: An in-house developed method for the quantitation of 7-alpha-hydroxy-4-cholesten-3-one by protein precipitation followed by liquid chromatography with tandem mass spectrometry was validated. Reference range of 1.8 – 57 ng/mL was determined using sera of 120 non-disease individuals. Results: Analysis of 189 patient samples yielded a mean concentration of 38.1 ng/mL (range, undetectable (< 0.5) - 331 ng/mL); 36.5% were low at < 15 ng/mL (carrying a negative predictive value (NPV) of 85%); 20.1% were high at >48 with 15.9% > 57. Most common accompanying ICD diagnoses were diarrhea unspecified, noninfectious gastroenteritis and colitis, hyperlipidemia/disorders of bile acid and cholesterol metabolism, Crohn’s disease, intestinal malabsorption, ulcerative colitis, IBS, change in bowel habit, obesity, NASH/fatty liver, gastroesophageal reflux, collagenous colitis, and rectal abscess. Of 14 patients with highest 7AlphaC4 levels (>100), more than one third (5/14, 36%) were Crohn’s disease patients with small intestine involvement (ileal resection status not known). Most common tests ordered at the same time or subsequent to 7AlphaC4, in order of frequency were tissue-transglutaminase IgA or other celiac tests, fecal calprotectin, fecal pancreatic elastase, stool PCR for 22 GI pathogens, Giardia, O&P, fecal fat, Helicobacter pylori, Clostridioides difficile toxin, and stool WBC. Conclusions: Here, we analyze results and orders associated with a new test for bile acid diarrhea, the blood-based bile acid precursor, 7AlphaC4 (also called 7AC4, 7C4, C4). More than half (56.6%) were low (< 15) or high (>48) and as such, potentially diagnostic, carrying a high NPV or high PPV for bile acids contributing to diarrhea. BAM/BAD may account for 30% of all chronic diarrhea cases and as such, may affect > 1% of the population. At the same time, disruptions in bile acid homeostasis and reabsorption occur more frequently in IBD (up to 40%, with or without ileal resection), and here, we observed that many of the highest 7AlphaC4 occurred in Crohn’s patients. Hence, 7AlphaC4 is a blood-based marker that may be helpful in providing quantitative evidence of the contribution of colonic bile acids toward diarrhea (and hence, a higher likelihood of responding to bile acid sequestrants), especially in patients with more than one possible etiology of diarrhea.