Gallstones are most commonly diagnosed with an abdominal ultrasound, which has an overall diagnostic accuracy of about 95% for stones in the gallbladder. But the full diagnostic process typically involves a combination of physical examination, blood tests, and sometimes advanced imaging, depending on where the stones are located and whether they’re causing complications.
What Happens During a Physical Exam
When you describe symptoms like upper-right abdominal pain, especially after fatty meals, your doctor will start with a physical exam. The most well-known test is called Murphy’s sign: your doctor presses on the right side of your abdomen, just below the ribcage, and asks you to take a deep breath. If you feel a sharp pain and instinctively stop breathing in, that’s a positive result. In one study, a positive Murphy’s sign was 97% sensitive and had a 93% positive predictive value for acute gallbladder inflammation.
That said, the test is less reliable in older adults. In patients over 70, the sensitivity drops to about 48%, and the positive predictive value falls to 58%. No single physical exam finding can confirm or rule out gallstones on its own, which is why imaging and blood work come next.
Abdominal Ultrasound: The First-Line Test
A standard abdominal ultrasound is the go-to imaging test for gallstones. It’s noninvasive, painless, widely available, and doesn’t use radiation. The transducer glides over your upper abdomen while you lie on your back, and the whole thing takes about 15 to 30 minutes. Gallstones show up as bright spots with shadows behind them, and the test also reveals signs of inflammation like thickening of the gallbladder wall or surrounding fluid.
For stones sitting in the gallbladder itself, ultrasound performs well, with a diagnostic accuracy around 95%. However, it’s much less reliable for stones that have moved into the common bile duct, the tube that drains bile into your intestine. Sensitivity for detecting bile duct stones drops to roughly 65%, and for tiny stones or sludge in the duct, it’s even lower at about 39%. So a normal ultrasound doesn’t always mean you’re stone-free, particularly if your symptoms or bloodwork suggest a stone is blocking bile flow.
Blood Tests That Point to a Problem
Blood tests don’t detect gallstones directly, but they reveal the downstream effects of a stone blocking bile drainage. Your doctor will typically order a liver panel and a complete blood count.
When a stone blocks the bile duct, bile backs up and a pattern called cholestasis appears on bloodwork. The most telling marker is alkaline phosphatase, an enzyme that rises to four or more times the normal level within one to two days of an obstruction. Bilirubin, the pigment that gives bile its color, also climbs. When the “direct” (conjugated) fraction makes up more than half of your total bilirubin, that points to a blockage rather than a liver problem. Liver enzymes called aminotransferases may rise modestly, typically in the 300 to 500 range, though a stone passing through the duct can cause a brief, dramatic spike.
If acute inflammation (cholecystitis) is suspected, your white blood cell count will often be elevated. This doesn’t tell your doctor where the problem is, but combined with imaging findings, it helps confirm that your gallbladder is actively inflamed rather than just harboring silent stones.
Why CT Scans Often Miss Gallstones
If you end up in the emergency room with abdominal pain, you may get a CT scan before anyone suspects gallstones specifically. CT is excellent for many abdominal emergencies, but it’s a poor gallstone detector. Only stones with enough calcium show up on CT, and many gallstones are made primarily of cholesterol, making them invisible to the scanner. Studies have found CT detects as few as 46% of gallstones. So if a CT scan comes back normal but your symptoms fit, an ultrasound is still needed.
Advanced Imaging for Bile Duct Stones
When ultrasound and blood tests suggest a stone has escaped the gallbladder and lodged in the bile duct, your doctor needs a closer look. Two specialized tests fill this role.
MRCP (Magnetic Resonance Imaging of the Bile Ducts)
MRCP is a specialized MRI that produces detailed 3D images of the bile ducts and pancreatic duct without any needles, sedation, or contrast dye injected into the ducts. You lie in an MRI machine for about 30 to 45 minutes. It’s the preferred next step when bile duct stones are suspected because it’s completely noninvasive and gives doctors a clear map of the ductal system. Recent evidence suggests MRCP can replace diagnostic invasive procedures for a wide range of bile duct problems, including stones, strictures, and other blockages.
ERCP (Endoscopic Procedure)
ERCP uses a flexible scope passed through your mouth, down through your stomach, and into the opening of the bile duct. Unlike MRCP, it’s invasive and requires sedation, but it has a major advantage: if a stone is found, the doctor can remove it during the same procedure. Because of this dual diagnostic-and-treatment capability, ERCP is now reserved primarily for situations where a bile duct stone is highly likely and treatment is planned, rather than used as a purely diagnostic test.
Endoscopic Ultrasound for Tiny Stones
Some gallstones are so small (under a few millimeters) that standard ultrasound misses them entirely. These microliths can still cause pain, pancreatitis, or recurring symptoms that are hard to explain. Endoscopic ultrasound (EUS) places a tiny ultrasound probe at the tip of an endoscope positioned right next to the gallbladder and bile duct, giving a much closer view than a scan through the abdominal wall. For microlithiasis that a standard ultrasound missed, EUS has a sensitivity between 93% and 100%. It’s typically used when symptoms are classic for gallstones but conventional imaging keeps coming back normal.
HIDA Scan: Testing Gallbladder Function
A HIDA scan (also called hepatobiliary scintigraphy) is a nuclear medicine test that tracks how well your gallbladder fills with and releases bile. A small amount of radioactive tracer is injected into a vein, and a camera follows it as your liver takes it up and passes it into the bile ducts and gallbladder. After the gallbladder fills, you’re given a medication that triggers it to squeeze, and the scan measures how much bile is ejected.
A normal gallbladder ejection fraction is above 30% to 35%. If yours falls below that threshold, it suggests chronic gallbladder inflammation or a condition called biliary dyskinesia, where the gallbladder doesn’t contract properly. The HIDA scan is also useful in acute situations: if the tracer never fills the gallbladder at all, that strongly suggests the cystic duct is blocked, which is the hallmark of acute cholecystitis. This is the test that Murphy’s sign is ultimately compared against when gauging its accuracy.
How the Pieces Fit Together
In practice, diagnosis follows a logical sequence. Symptoms and a physical exam raise suspicion. An abdominal ultrasound confirms stones in the gallbladder in most cases. Blood tests reveal whether a stone is causing a blockage or inflammation. If bile duct stones are suspected, MRCP provides a noninvasive look, and ERCP follows only if a stone needs to be removed. For stubborn diagnostic puzzles, where symptoms persist but standard ultrasound is negative, endoscopic ultrasound or a HIDA scan fills the gap.
Most people with straightforward gallstone pain will only need an ultrasound and basic blood work before moving to a treatment discussion. The more complex tests are reserved for complications, unclear cases, or when the stone has traveled beyond the gallbladder itself.