7AlphaC4 (7 alpha-hydroxy-4-cholesten-3-one)

7AlphaC4 is a diagnostic blood test for diarrhea due to excess colonic bile acids.

Bile acids (BAs) are detergent molecules necessary to emulsify fat and facilitate interstinal absorption of lipids and fat-soluble vitamins. When BA reabsorption in the ileum is impaired, more BAs in the colon cause loose or watery stool while less BAs re-entering enterohepatic circulation results in increased hepatic BA synthesis (due to less negative feedback inhibition).

7 Alpha-hydroxy-4-cholesten-3-one (7AlphaC4) is an intermediate in the synthesis of BAs from cholesterol. With increased hepatic BA synthesis, 7AlphaC4 concentrations in serum also increase. Elevated serum 7AlphaC4 can be diagnostic of bile acid malabsorption (BAM) or bile acid diarrhea (BAD).

BAM/BAD results from impaired ileal reabsorption (e.g. in Crohn's disease, radiation ileitis, ileal resection), increased BA production (many cases of functional diarrhea and diarrhea-predominant irritable bowel syndrome (IBS-D)), or excess hepatic BA synthesis (in hypertriglyceridemia and in patients on metformin therapy).

BAM/BAD occurs in up to 50% of functional diarrhea and in 33-60% of IBS-D and is co-existent in 35% of microscopic colitis and in 42% of inflammatory bowel disease (IBD) with or without ileal disease.