Gallstones are most commonly found with an abdominal ultrasound, a painless imaging test that detects stones with about 94% accuracy. But depending on your symptoms and where stones might be lodged, your doctor may use a combination of physical exams, blood tests, and more specialized imaging to get the full picture.
The Physical Exam
Before any imaging, your doctor will press on the upper right side of your abdomen, just below your ribs. This is where your gallbladder sits. If a gallstone is causing inflammation, you’ll feel a sharp spike in pain when you try to breathe in while the doctor applies pressure. This maneuver is called Murphy’s sign, and it’s about 97% sensitive for detecting active gallbladder inflammation. A positive result doesn’t confirm stones on its own, but it tells your doctor to move quickly to imaging and blood work.
Blood Tests That Point to a Blockage
Blood tests can’t show gallstones directly, but they reveal the damage stones cause when they block bile flow. Your doctor will typically order a panel of liver function tests looking for a few key markers.
Bilirubin is a waste product your liver processes and sends out through bile. When a stone blocks the bile duct, bilirubin backs up into your bloodstream, which can turn your skin and eyes yellow. Alkaline phosphatase, a liver enzyme, jumps to four or more times its normal level within one to two days of a blockage, regardless of where the obstruction sits. Liver enzymes called ALT and AST also rise, sometimes dramatically, when a stone is passing through the common bile duct. Together, these markers help your doctor determine whether a stone is just sitting quietly in the gallbladder or actively blocking something.
Abdominal Ultrasound: The First-Line Test
A standard abdominal ultrasound is the go-to test for gallstones. It’s quick, widely available, uses no radiation, and picks up gallbladder stones with a pooled sensitivity of 94% and specificity of 93%. The technician applies gel to your abdomen and moves a handheld probe over the area. Sound waves bounce off the stones and create a visible shadow on the screen, making them relatively easy to spot.
You’ll need to fast for 8 to 12 hours beforehand. Fasting keeps your gallbladder full of bile, which makes it balloon out and gives the ultrasound a clearer view. It also reduces gas buildup in your abdomen, which can interfere with the image. Most people have the test done first thing in the morning after skipping breakfast. The exam itself takes about 15 to 30 minutes, and results are often available the same day.
When Tiny Stones Get Missed
Standard ultrasound occasionally misses very small stones or sludge, the thick, gritty sediment that can form in the gallbladder. If your symptoms strongly suggest gallstones but the ultrasound comes back normal, your doctor may order an endoscopic ultrasound (EUS). This test places a tiny ultrasound probe on the end of a thin, flexible tube that’s guided through your mouth and into your upper digestive tract, getting much closer to the gallbladder and bile ducts than an external probe can.
The difference in detection is striking. In one study of 35 patients who had normal standard ultrasounds but ongoing gallstone-type pain, endoscopic ultrasound found gallbladder sludge or small stones in 33 of them. EUS has a sensitivity of 94% to 98% for these tiny stones, making it the best tool when conventional imaging falls short.
CT Scans and MRCP for Bile Duct Stones
A CT scan is often done in emergency settings because it’s fast and good at ruling out other causes of abdominal pain. However, it’s not great at finding gallstones specifically. CT catches only about 50% of stones in the bile ducts, since many stones don’t show up well on standard X-ray-based imaging.
MRCP (magnetic resonance cholangiopancreatography) is a specialized MRI that creates detailed images of the bile ducts and pancreatic ducts without radiation or contrast dye injected into the ducts. It detects bile duct stones with roughly 73% to 75% sensitivity, significantly outperforming CT. Your doctor will typically order MRCP when blood tests suggest a stone has moved out of the gallbladder and into the common bile duct, a situation that can cause more serious complications like pancreatitis or infection.
The test itself feels like a regular MRI. You lie inside the scanner for 30 to 45 minutes while it takes images. No needles, no sedation, no recovery time.
HIDA Scan: Testing Gallbladder Function
Sometimes the question isn’t whether you have stones but whether your gallbladder is working properly. A HIDA scan answers this by tracking a small amount of radioactive tracer as it moves from your bloodstream through your liver, into your gallbladder, and out into your small intestine.
If the tracer never shows up in your gallbladder, that’s a strong sign of acute inflammation, likely from a stone blocking the duct that connects the gallbladder to the rest of the biliary system. The scan also measures your gallbladder ejection fraction, which is how much bile the gallbladder squeezes out when stimulated. A normal ejection fraction is above 30% to 35%. A number below that range suggests the gallbladder isn’t contracting well, a condition called biliary dyskinesia, which can cause symptoms identical to gallstones even when no stones are present.
ERCP: Diagnosis and Treatment in One Procedure
ERCP is the most invasive test on this list, but it has a unique advantage: your doctor can remove stones during the same procedure. A flexible scope is threaded through your mouth, down through your stomach, and into the opening where the bile duct empties into the small intestine. Contrast dye is injected into the ducts, and X-rays capture real-time images of any blockages.
If a stone is spotted in the bile duct, the doctor can widen the duct opening and extract it right then. Because ERCP carries a 5% to 10% complication rate (primarily inflammation of the pancreas), it’s not used as a first-line screening tool. It’s reserved for situations where blood tests and imaging have already identified or strongly suggested a bile duct stone that needs to be removed.
The Typical Diagnostic Sequence
In practice, the testing process follows a predictable path. You describe your symptoms, typically pain in the upper right abdomen after eating, sometimes with nausea. Your doctor does a physical exam and orders blood work alongside an abdominal ultrasound. For most people, the ultrasound confirms the diagnosis and no further testing is needed.
If the ultrasound is normal but your symptoms persist, endoscopic ultrasound may be the next step. If blood tests suggest a stone has migrated into the bile duct, MRCP maps the ducts noninvasively, and ERCP follows if a stone needs to be retrieved. A HIDA scan enters the picture when imaging shows no stones but your symptoms point squarely at the gallbladder. Each test builds on the last, narrowing the diagnosis until your doctor has a clear answer and a plan.