Chenodeoxycholic Acid (CDCA), % of Bile Acids

Bile acids can contribute to persistent loose, urgent stools. But the percentage of one bile acid in stool doesn't establish whether bile acids are causing your symptoms. Chenodeoxycholic acid (CDCA) percentage describes the composition of the sample, and its interpretation depends on the other bile acids present.

This test uses LC-MS to report CDCA as a percentage of the bile acids measured in stool. Its standalone clinical use remains exploratory. Research on stool CDCA concentrations and combined primary bile acid percentages supports interest in this measurement, but those results aren't interchangeable with CDCA percentage alone. There is no established treatment target for this individual percentage.

How Bile Travels From Your Liver to Your Stool

Your liver makes two main primary bile acids from cholesterol: cholic acid and CDCA. They help your small intestine absorb dietary fat. Most bile acids are reabsorbed and returned to the liver for reuse.

Before release, your liver usually attaches glycine or taurine to bile acids. Gut bacteria can remove these attachments, leaving unconjugated bile acids. Certain bacteria then convert CDCA into lithocholic acid (LCA) and cholic acid into deoxycholic acid (DCA). These products are secondary bile acids, which commonly dominate the stool bile acid profile.

The CDCA component reported here is distinct from its glycine-linked, taurine-linked, and sulfated forms. Studies of those other molecules can help explain bile acid biology, but they don't directly establish what this percentage means.

What the Percentage Represents

Your result depends on both CDCA and the other bile acids included in the laboratory's total. Its percentage can rise because CDCA increases, because other bile acids decrease, or both. The reverse can lower the percentage. It doesn't measure the total amount of bile reaching your colon or the fraction of all liver-produced CDCA that escaped bacterial conversion.

Bile production, intestinal reabsorption, bacterial activity, and transit time can all affect the stool profile. Fast transit may leave less time for bacterial conversion, while changes in converting bacteria can alter the profile even without diarrhea. A percentage alone cannot separate these explanations.

Chronic Diarrhea and IBS-D

CDCA in the colon can stimulate fluid secretion and bowel movement. In a study of 55 adults with diarrhea-predominant irritable bowel syndrome and 28 healthy controls, stool CDCA concentrations were substantially higher in the IBS group. Higher concentrations were weakly associated with more frequent bowel movements and, in a smaller subgroup, with a lower threshold for first sensing rectal stretching. The study also found fewer bacteria from the Ruminococcaceae family.

That study used a related LC-MS method but reported CDCA as an amount per gram of stool. It did not establish a diagnostic threshold for this percentage. Other research and clinical testing use the combined percentage of cholic acid and CDCA, sometimes alongside blood C4 or a timed stool collection. Evidence for that combined measurement cannot be assigned to CDCA percentage alone.

Constipation and Slow Transit

Slower transit can change bile acid conversion and reabsorption. In one study, a minority of adults with constipation-predominant irritable bowel syndrome, roughly 15%, had reduced total bile acid excretion during a timed stool collection. Lower excretion was associated with slower colon transit. This finding concerns total bile acid output and doesn't establish that a low CDCA percentage causes constipation.

A study in children found that most with functional constipation had bile acid profiles similar to controls. A small subgroup had abundant sulfated CDCA, which has reduced fluid-secreting activity. Sulfated CDCA is a different molecule from the CDCA component reported here, so this percentage cannot identify that pattern.

Fatty Liver, Fibrosis, and Cirrhosis

Human studies have linked liver disease with altered stool bile acids. A 2022 study compared adults with biopsy-confirmed fatty liver disease and healthy controls. Stool primary bile acid concentrations, including CDCA, were higher in groups with more advanced liver scarring. These were comparisons between people at different disease stages, not evidence that a rising percentage tracks scarring within one person.

A cirrhosis study found lower secondary-to-primary bile acid ratios and changes in bacteria associated with bile acid conversion. Its stool measurements used a different laboratory method from this LC-MS test. Advanced disease and its treatments could both affect the findings.

The pattern isn't consistent across studies. A 2025 study of fatty liver disease found higher blood bile acids with advanced fibrosis but no difference in total stool bile acid concentrations. Stool CDCA percentage has not been validated to diagnose fatty liver, stage fibrosis, or determine whether scarring is progressing.

Colorectal Cancer Research

A 2025 meta-analysis found higher stool CDCA concentrations in people with colorectal cancer and in groups considered at increased risk. The included studies compared people with different existing conditions or risk factors. They didn't establish that CDCA rises before cancer develops.

The studies used concentration measurements and varied laboratory methods, rather than a standardized standalone CDCA percentage. This result has no established role in colorectal cancer screening. Neither a low nor a high percentage can determine whether you have cancer.

Why Lower Isn't Necessarily Better

A low percentage can reflect conversion to other bile acids, reduced delivery of CDCA, or an increase in other components of the sample. It doesn't prove excessive bacterial conversion or damage to your gut lining. A high percentage likewise doesn't prove that your microbiome is unhealthy.

Primary and secondary bile acids have different effects that depend on the individual molecule, its concentration, and where it acts. The available human evidence doesn't establish that deliberately raising or lowering this stool percentage improves health.

When Results Can Be Misleading

Stool bile acids vary between bowel movements and across days. A single sample may not represent your average bile acid output. Some clinical protocols combine a random stool primary bile acid percentage with blood testing, while others use a timed collection. Their validation applies to those specific combinations and collection procedures.

• Antibiotics: oral vancomycin increased stool CDCA concentration and reduced LCA in a small randomized study with eight volunteers receiving vancomycin. This was a concentration finding during treatment, not proof of a particular percentage change or of an infection caused by that change. Antibiotic exposure also complicates interpretation of bacterial conversion.
• Laxatives and antidiarrheals: senna and loperamide changed transit and stool bile acid profiles in healthy volunteers. Medication-related changes don't establish an underlying bile acid disorder.
• Bile acid treatments: bile acid binders and medicines that alter bile acid supply or reabsorption can change the profile. A binder can increase bile acids recovered from stool while improving diarrhea, so greater stool excretion during treatment doesn't necessarily mean greater exposure to active, unbound bile acids.
• Changes in the denominator: CDCA's percentage can change when other bile acids change. A stable percentage can also conceal changes in the amounts of several bile acids.
• LC-MS limitations: LC-MS separates individual bile acids before detecting them. Accuracy still depends on extraction from stool, separation of similar molecules, and control of interference from other sample components. Storage and repeated freezing and thawing can affect recovery. Precision reported for a blood assay cannot be assumed for this stool assay.

Laboratories can measure different sets of bile acids and use different preparation and calculation procedures. Even two LC-MS reports may therefore have different totals underlying their percentages.

What a Trend Can Establish

Repeated measurements may show whether a pattern persists under similar conditions. They haven't been shown to turn this percentage into a reliable measure of microbiome recovery, liver scarring, cancer risk, or treatment success. There is also no established size of change that separates meaningful improvement from ordinary biological and laboratory variation.