Urine Bile Salts

A traditional bedside urine test for bile salts, reported as present or absent. It is not part of routine urinalysis at large US labs and is not very reliable on its own.

AI-drafted. Awaiting verificationLOINC 43889-5

What it is

Bile salts are made by the liver and released into bile to help you digest fat. Healthy urine normally has very little. The usual method is Hay's sulfur (sulphur) test. A lab sprinkles fine sulfur powder on the urine. If bile salts are present, they lower the surface tension of the urine and the powder sinks. The result is reported as present or absent. Some labs still include it on urine reports.

Why it matters

A positive result has traditionally been read as a hint that bile is not draining normally, as can happen with a blocked bile duct or some liver conditions, often alongside bilirubin in the urine. The test is crude and can't tell causes apart. Clinicians usually turn to blood tests, such as bilirubin and liver enzymes, to learn more. A negative result does not rule out a liver or bile duct problem.

If it’s high

A positive result means the urine lowered the surface tension enough for the sulfur to sink. This has traditionally been linked to bile salts reaching the urine when bile does not flow normally. It can also be a false positive, because the test is not specific. Your clinician can sort out which it is with blood tests and your symptoms.

Common causes

A result not caused by bile salts at all, since the sulfur sinks whenever the urine's surface tension drops, and other things such as its salt content and acidity also affect that
A blockage in the bile ducts, for example from gallstones
Liver conditions that cause jaundice, such as hepatitis
Inherited conditions that slow bile flow, which are uncommon

What can help

Ask whether blood tests for bilirubin, liver enzymes or bile acids would give a clearer picture
Mention symptoms such as yellow skin or eyes, dark urine, pale stools, itching or belly pain
Tell your clinician about every medicine and supplement you take, and about alcohol use

What can affect your result

Technique: the test is done by eye, so it depends on how the powder is added and read
Sample freshness and cleanliness of the container
Other things that change the urine's surface tension, such as its salt content and acidity
Your lab's practice: large US labs such as Labcorp do not list it in their complete urinalysis
The test responds to a drop in the urine's surface tension, so it is not specific to bile salts.
It is done by eye, so results depend on technique and the person reading it.
A sample that is old, or collected in a container that is not clean, may not reflect your urine at the time.

Any time. A fresh urine sample is tested soon after collection. Reflects the sample at the moment of collection.

When to talk to a clinician

A positive bile salts result is worth mentioning to your clinician, who can decide whether blood tests would help. Reach out soon if you also notice yellow skin or eyes, tea-colored urine, pale stools, itching, nausea or belly pain. Get urgent care if yellow skin or eyes come with severe belly pain, fever or chills, or confusion.

Questions you could ask

Does the rest of my urine report, such as bilirubin and urobilinogen, change how you read this?
Should we check blood tests for bilirubin and liver enzymes?
Could a medicine, a supplement or the way the sample was handled explain this result?
Should this urine test be repeated with a fresh sample?

Questions people ask

What is Hay's test?

It is a quick bench test for bile salts in urine. Sulfur powder is sprinkled on the urine, and if it sinks, bile salts may be present. Reports usually show it as present or absent.

Are bile salts and bile pigments the same thing?

No. Bile pigments mean bilirubin, the yellow pigment from old red blood cells. Bile salts help digest fat. They are tested separately, and your report may list both.

Does a positive result mean I have a liver problem?

Not by itself. The test is crude, and false positives happen. A positive result is a reason to ask your clinician about blood tests that look at the liver and bile ducts more directly.

Show the science and sources

For clinicians and researchers

Hay's sulfur test is a qualitative bench test. Finely powdered sulfur floats on normal urine because of surface tension. Bile salts (conjugated bile acids) act as surfactants and lower the surface tension, so the powder sinks. A 2015 review reports an inverse relationship between urine surface tension and bile salt concentration, with surface tension also falling in jaundice, but it names sodium chloride as another constituent that affects surface tension and lists age and acidity as other influences. Because the readout is a physical change in surface tension, it is not chemically specific. A 1951 clinical review called urine bile salt testing not very satisfactory or useful. Routine automated urinalysis in the US does not include it: Labcorp's complete urinalysis component list has no bile salts line. Bile pigments on the same report are bilirubin, which is measured by a different, dipstick or diazo method (see the urine bilirubin marker). Quantitative urinary bile acids are a separate specialist mass-spectrometry test that looks for metabolic abnormalities of bile acids, and serum total bile acids are the usual blood measurement. The closest LOINC code is 43889-5, Bile acid [Presence] in Urine.

LOINC 43889-5 (primary). Specimen: urine.

Sources

Hay's test, Wikipedia
Liver Function Tests, Bristol Medico-Chirurgical Journal (1951)
Clinical Methods: Chapter 191, Urinalysis, Butterworths (NCBI Bookshelf) (1990)
Urinalysis, Complete With Microscopic Examination (test 003772), Labcorp
FBAC: Bile Acids, Urine, Cincinnati Children's Hospital Medical Center (Mayo Clinic Laboratories Extended Catalog)
Surface tension in human pathophysiology and its application as a medical diagnostic tool, BioImpacts (2015)

AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.