Gallbladder Ejection Fraction: A Number Without Its Protocol

A gallbladder ejection fraction under 35% with a clean ultrasound is the working definition of a lazy gallbladder in most operating rooms. It is the number that decides who loses an organ. It is also a protocol artifact, and for years I ordered it and treated its cutoff as a fact of nature.

Chapter 23 of The Angry Gut, Bile Is a Hormone, Not Soap, makes the physiological case. What follows is the measurement case: what that percentage is made of, what bile actually signals, and what terrain grew the stone in the first place.

What the gallbladder ejection fraction cutoff is built from

The normal range everyone quotes came from 60 healthy volunteers at four centers. The lower limit of normal landed at 38%, defined at the 1% confidence bound, and the scatter depended entirely on how the stimulating hormone was infused. At best the coefficient of variation was 19% with a 60-minute infusion. With the short infusion in common use it was 52%, and at 30 minutes, 35%.

So the reproducibility is worse than the distance between a normal and an abnormal result. That study enrolled volunteers only, and it was built to describe normal, never to show that a low number predicts benefit from surgery.

What does predict benefit is the symptom pattern. In 93 consecutive patients with documented dyskinesia the stimulated fraction was the same in those who improved after surgery and those who did not, 19 plus or minus 9% against 16 plus or minus 7%. Patients with classic biliary pain were 22 times more likely to be relieved, and 97% of them were. Among the atypical patients, 9 of 32 got better with no operation at all. A threshold with no protocol attached is a number wearing a lab coat, which is the same problem as a liver enzyme read without its context.

Sludge is a weather report

The other word that gets an organ removed is sludge. Ultrasound found it in 1.7% of 17,021 patients, and on repeat imaging most of it was gone: 71.4% cleared inside roughly two months, with stones appearing in 8.9% and acalculous cholecystitis in 7.1%.

Do not read that as permission to ignore it. Followed forward, stones or complications such as acute cholecystitis occurred in 19.6%, on a small denominator of 56 people who grew sludge under observation over a mean of 20.3 months, and the stones that appeared stayed silent. One in five is not nothing. It is an argument for a watching plan with a date on it.

Bile is a hormone, and the signal is graded

Here is what the ejection fraction cannot see. Expose human ileal tissue to one bile acid at a time and the half-maximal response for fibroblast growth factor 19 comes at 20 micromolar of chenodeoxycholic acid, a concentration the ileum reaches after a fatty meal. The receptor is tuned to a dinner, not to a pharmacological dose.

Then the ladder. Against chenodeoxycholate, cholate produced 81% of the response, deoxycholate 40% and lithocholate 4%. Those last two are secondary bile acids, which your bacteria make out of the primary ones. This is cultured tissue, and it measures transcript rather than blood sugar.

Read what that means for terrain work. Your flora sets the volume on a hormone your own ileum makes, because the bacteria decide which bile acids exist to be read in the first place. The loop then runs back the other way, since bile is what keeps the upper gut thin and shapes who lives there. Community and signal write each other, which is the mechanism under a microbiome that drives symptoms elsewhere.

Why one blood draw cannot score this system

In a living person the axis runs on a clock. Basal levels of that growth factor vary ten-fold between normal people. They fall when bile acids are bound in the lumen and rise when they are fed, peak 90 to 120 minutes after the meal-driven rise in serum bile acids, and fasting abolishes the rhythm altogether.

There is no reference interval waiting to be quoted here. When synthesis doubled after gallbladder surgery, serum bile acids, cholesterol and triglycerides did not budge. The tissue is a hormone source, and the routine panel cannot see it.

A number is only useful when its protocol, its timing and its reference group travel with it, which is the standard behind testing whether a body can heal rather than collecting results.

What a drug bought at that receptor, and what it cost

The obvious move was to hit the receptor with a molecule, and that experiment has run its course. In 20 patients on a synthetic agonist the growth factor rose from 95.0 to 234.4 ng/L while the liver’s bile acid synthesis collapsed from 31.4 to 2.8 nmol/L, and the bile in the gallbladder went dilute, 77.9 against 196.4 mmol/L on placebo, with its cholesterol saturation index up to 2.8 from 1.8. More detergent, less able to hold cholesterol in solution.

In the large fibrosis trial a blinded re-read found improvement in 22.4% on the higher dose against 9.6% on placebo, disease resolution missed significance, and itch appeared in 51% of patients on the high dose against 19%. Accelerated approval came in May 2016; withdrawal came in November 2025. So the axis is real and reachable, and the flagship molecule aimed at it is off the market. Your own physiology aims a meal at that receptor daily, in a pulse, with an off switch. A tablet has none of those, which is why the interventions that open drainage are where this lands.

The terrain that grew the stone

Now the metabolic half, which is usually read backwards. Among 4,307 people in a population cohort, 67.2% of those without a gallbladder carried metabolic syndrome, against 51.9% of those who still had one, while moderate-to-severe fatty liver ran 42.7% against 34.2%. Those scans came a median of ten years after surgery, and adjusting for metabolic factors makes both associations disappear.

The critic’s reading is fair and I concede most of it: only 265 of those participants had lost a gallbladder, steatosis was graded on ultrasound rather than biopsy, and one shared cause can produce both the stone and the fatty liver. The inference is where I stop. Adjusting for body weight and diabetes removes the effect only if you treat those as confounders rather than as the path itself. The stone is a symptom of the terrain: bile made under high insulin, loaded with cholesterol, in a reservoir rarely asked to empty. A cohort can adjust that away; a practice walks in with the patient.

Two more drivers sit upstream of the knife. Among gallstone carriers, 65.7% report indigestion, a figure built mostly from studies without validated criteria, and the reviewers warned of operations that leave the complaint behind. Then the guideline driver: decades of low-fat advice kept the organ quiet, yet fat reaching the duodenum is what empties it. Bile that sits concentrates into sludge. That is a policy failure, not a patient failing, and it belongs beside the inflammatory terrain.

What is worth measuring instead

Sluggish liver and congested biliary system cannot be measured. No hepatology criterion returns a number for either. A real biliary measurement looks different: quantitative imaging that tracked 14 duct metrics and caught a rising stricture count over a median 371 days while blood tests stayed flat.

So ask what protocol produced your ejection fraction, whether your pain was the classic biliary pattern, and when any sludge gets rescanned. Settle the plan with the physician who prescribes, since nothing here is a reason to start or stop a medication. The Deep Dive for Chapter 23 lists every study and every number above, with what each result shows, what it does not, and the one that argues against my own position. What the flora do to appetite comes next.

Frequently asked questions

What is a normal gallbladder ejection fraction?

In 60 healthy volunteers at four centers the lower limit of normal came out at 38%, and the reproducibility depended on the infusion: a coefficient of variation of 19% with a 60-minute infusion, 52% with the short one, 35% at 30 minutes. A percentage quoted without its protocol cannot be interpreted. Ask which protocol produced yours. Context is what makes a number usable.

Does a low ejection fraction mean I need surgery?

It does not settle it. In 93 patients the number was the same whether the operation helped or not, while classic biliary pain predicted relief 22 times over, and 9 of 32 atypical patients improved with no operation. A real biliary indication is a good reason to operate. An ambiguous percentage on its own is not. Imaging findings need a matching clinical picture.

Can a blood test show whether my bile signaling works?

Not reliably. Basal levels of the relevant hormone vary ten-fold between healthy people, peak 90 to 120 minutes after a meal, and vanish on a fast, which is when blood is usually drawn. After gallbladder surgery doubled bile acid synthesis, serum bile acids and lipids did not move at all. The routine panel is blind to this axis. Measure what responds to treatment instead.

Is gallbladder sludge dangerous?

Mostly it clears: 71.4% of the patients followed with repeat scans were clear within about two months. Followed forward, though, stones or complications occurred in 19.6%, on a denominator of 56 people watched for a mean of 20.3 months. That is an argument for a scheduled repeat scan rather than either a scalpel or a shrug. Watchful plans need dates, not vibes.

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Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP, board certified in anesthesiology, pain medicine, interventional pain management, addiction medicine and obesity medicine. Adapted from Chapter 23 of The Angry Gut by Dr. Padda and Ami Michelle Grimes. Last reviewed September 2026.