Gallstones are most commonly detected with an abdominal ultrasound, a painless imaging test that picks up stones in the gallbladder with about 94% accuracy. But ultrasound is just one piece of the diagnostic process. Depending on your symptoms and where stones may be lodged, your doctor might use blood tests, specialized scans, or more advanced imaging to get the full picture.
What Happens Before Any Test
Testing for gallstones typically starts with a physical exam. Your doctor will press on the upper right side of your abdomen and ask you to take a deep breath. If your inflamed gallbladder makes contact with the examiner’s hand and you involuntarily stop breathing from pain, that’s called a positive Murphy’s sign. It’s a useful clue, with about 80% diagnostic accuracy for acute gallbladder inflammation, but it’s not reliable enough on its own. In older adults especially, a negative result doesn’t rule anything out.
Your doctor will also ask about the nature of your pain. Biliary colic, the hallmark symptom of gallstones, is a steady, intense ache in the upper right abdomen that often radiates to the back or right shoulder. It typically starts after eating and lasts 30 minutes to several hours. Notably, general symptoms like gas, bloating, and nausea are not specific to gallstones. These complaints show up at roughly equal rates in people with ulcers, functional gut disorders, and gallbladder disease. Fatty foods are also not a reliable trigger, despite the common belief.
Abdominal Ultrasound: The First-Line Test
An abdominal ultrasound is the standard first test when gallstones are suspected. The American College of Radiology recommends it as the go-to imaging study for right upper quadrant pain. It uses sound waves to create images of your gallbladder and bile ducts, and it involves no radiation.
You’ll need to fast for six hours before the scan. During this fasting period, you can drink small amounts of clear fluids up until about two hours before the appointment. Fasting matters because it keeps your gallbladder full of bile, which makes stones much easier to see. A gallbladder that has recently contracted after a meal can obscure small stones.
The test itself takes about 15 to 30 minutes. A technician applies gel to your abdomen and moves a handheld probe across the area. It’s painless, though you may feel some discomfort if the probe presses on an inflamed gallbladder. Pooled data across studies show ultrasound detects gallstones with 94% sensitivity and 93% specificity, making it both highly accurate at finding stones and reliable at ruling them out.
That said, standard ultrasound is less effective at spotting stones that have moved out of the gallbladder and into the common bile duct. One study found its sensitivity for bile duct stones dropped to just 39%, meaning it misses more than half of them.
Blood Tests That Signal a Problem
Blood work doesn’t detect gallstones directly, but it reveals whether a stone is causing a blockage or other complications. Your doctor will typically order a panel that includes liver enzymes and bilirubin levels.
When a gallstone blocks a bile duct, alkaline phosphatase (a liver enzyme) rises to four or more times its normal level within one to two days. Other liver enzymes may also rise, sometimes dramatically if a stone is passing through the common bile duct, though the increase tends to be more modest in chronic or partial blockages. Bilirubin, the pigment that gives bile its color, builds up in the blood when bile can’t drain properly. If levels climb high enough, bilirubin spills into the urine, turning it noticeably dark.
Normal blood work doesn’t rule out gallstones. Up to 80% of people with gallstones have no symptoms at all, and their liver function tests are completely normal. Blood tests are most useful when your doctor suspects a complication like a blocked duct, infection, or pancreatitis.
HIDA Scan: Testing Gallbladder Function
If your ultrasound looks normal but your symptoms strongly suggest a gallbladder problem, your doctor may order a HIDA scan (also called cholescintigraphy). This nuclear medicine test evaluates how well your gallbladder fills and empties rather than looking for stones directly.
A small amount of radioactive tracer is injected into a vein. It travels through your bloodstream to the liver, into the bile, and then into the gallbladder. A camera tracks the tracer’s movement over about an hour. Partway through, you’ll receive an injection of a hormone that stimulates your gallbladder to contract, and the scan measures what percentage of bile it squeezes out.
A normal gallbladder ejects at least 38% of its contents. Below that threshold, the diagnosis is biliary dyskinesia, a condition where the gallbladder doesn’t empty properly. If the tracer never enters the gallbladder at all, that suggests the cystic duct is blocked, which points to acute cholecystitis (gallbladder inflammation).
MRCP: The Best Test for Bile Duct Stones
Magnetic resonance cholangiopancreatography, or MRCP, is a specialized MRI that produces detailed images of the bile ducts and pancreatic duct. It’s the preferred non-invasive test when doctors suspect a stone has left the gallbladder and become lodged in the common bile duct, a condition called choledocholithiasis.
CT scans are a cornerstone of emergency abdominal imaging, but they have limited sensitivity for bile duct stones. Many gallstones are made of cholesterol, which doesn’t show up well on CT. When clinical suspicion for a duct stone persists despite a negative CT, MRCP is the recommended next step. Current evidence strongly supports MRCP as the preferred imaging study to confirm or exclude bile duct stones when the diagnosis is uncertain.
The test requires no contrast dye injection and takes about 30 to 45 minutes inside an MRI machine. You’ll need to fast beforehand, similar to the preparation for ultrasound. It’s painless but can be uncomfortable if you’re claustrophobic.
ERCP: Diagnosis and Treatment in One Procedure
Endoscopic retrograde cholangiopancreatography (ERCP) is both a diagnostic and therapeutic procedure, but doctors generally reserve it for situations where they expect to treat a problem during the same session. It’s not a screening test.
During ERCP, a flexible scope is passed through your mouth, down through your stomach, and into the first part of your small intestine where the bile duct opens. Contrast dye is injected into the duct system and X-rays are taken to visualize stones or blockages. If a stone is found, the doctor can often remove it on the spot by widening the duct opening and extracting the stone with a small basket or balloon.
Because ERCP carries a small risk of complications (including pancreatitis), it’s typically used only after less invasive imaging has identified or strongly suggested a bile duct stone that needs removal.
Endoscopic Ultrasound for Tiny Stones
Standard abdominal ultrasound can miss very small stones, sometimes called microlithiasis, as well as stones in the bile duct. When suspicion remains high despite normal imaging, endoscopic ultrasound (EUS) offers a closer look. This test places an ultrasound probe at the tip of an endoscope, positioning it right next to the gallbladder and bile ducts from inside the digestive tract.
EUS detects gallbladder microlithiasis with nearly 99% sensitivity and 100% specificity. For common bile duct stones, its sensitivity is about 93%, compared to roughly 39% for standard ultrasound. It requires sedation and is more invasive than a regular ultrasound, so it’s reserved for cases where other tests have been inconclusive.
When Gallstones Are Found by Accident
Many gallstones are discovered incidentally during imaging ordered for a completely unrelated reason. This is common: up to 80% of people with gallstones never experience symptoms. These “silent” stones show up on CT scans, ultrasounds, or MRIs performed for other conditions.
Finding gallstones on a scan doesn’t necessarily mean they’re causing your symptoms. Gallstones do not cause dyspepsia or fat malabsorption, and nonspecific complaints like bloating and gas aren’t reliable indicators of gallbladder disease. The key distinction is whether you’ve experienced true biliary colic. If the stones are genuinely asymptomatic and you have no complications, treatment is typically not recommended. Most silent gallstones never cause problems, though a small percentage of people will eventually develop symptoms over time.