Table 1. Current and future bile acid diarrhea (BAD) diagnostic tests (BA=bile acids; primary BAs are cholic acid and chenodeoxycholic acid). Information in pediatric patients is limited.
Amount of primary bile acids reflects direct or indirect secretory potential (CDCA and CA respectively, as CA undergoes 7α hydroxylation in the colon to form the secretory, deoxycholic acid). Modified with permission from ref. 29, Vijayvargiya P, Camilleri M. Commentary: Current practice in the diagnosis of bile acid diarrhea. Gastroenterology 2019;156:1233–1238.
| Diagnostic Test | 75SeHCAT | Fasting serum C4 | Fasting serum FGF19 | Total fecal BAs | Primary BAs >4% + total fecal BAs | Fecal primary BAs >10% | Combined tests of fecal primary BAs + fasting serum C4 |
|---|---|---|---|---|---|---|---|
| What does it measure? | Ileal capacity to reabsorb radio-labeled bile acid retention (%) on day 7 | Hepatic bile acid synthesis | Amount of feedback inhibition to hepatic bile acid synthesis | Total fecal bile acid excreted from the colon | Amount of primary bile acids reflects direct or indirect secretory potential (CDCA and CA respectively) with total fecal BA excretion | Amount of bile acids that are directly synthesized from the liver with secretory potential | Combining serum and stool biomarkers to simplify diagnosis of bile acid diarrhea |
| Diagnostic cutoffs | <5% (severe) <10%+ (moderate) <15% (mild) |
≥52.5 ng/mL | ≤61.7 pg/mL | ≥2,337 μmol/48h | Primary BA >4% + total fecal BA >1,000 μmol/48h | >10% primary BA | Fecal sample primary BA >10% + serum C4 ≥52.5 ng/mL |
| Sensitivity relative to fecal wt >400g/48h | 15% | 28% | 59% | 46% | 49% | ||
| Specificity relative to fecal wt >400g/48h | 86% | 75% | 92% | 97% | 91% | ||
| Diet, radiation and equipment required for measurement | γ camera + radiation exposure; 7-day test | HPLC; Measure before 9am |
ELISA; Measure before 9am |
HPLC Requires 100-gram high fat diet × 4 days and 2-day stool collection |
HPLC + HPLC single, random stool sample + C4 measured before 9am |
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| Comment or pitfalls of testing | ? best for type I BAD | ? diagnostic accuracy | ? diagnostic accuracy | Analysis of fecal BAs reflects BA in colon | Identify additional patients | Identify additional patients | Identifying BAD based on 48h fecal BA: 63% Sensitivity with 90% specificity |