Gallstones are typically diagnosed with an abdominal ultrasound, which detects stones in the gallbladder with about 94% accuracy. But the diagnostic process usually involves more than just one scan. Depending on your symptoms and where stones may be lodged, your doctor will use a combination of physical examination, blood tests, and sometimes advanced imaging to get the full picture.
What Happens During the Physical Exam
The first step is a hands-on evaluation. Your doctor will press on the upper right side of your abdomen, just below your rib cage, and ask you to take a deep breath. If the pain sharpens as you inhale, that’s a positive Murphy’s sign, a test that’s about 97% sensitive for acute gallbladder inflammation. It works because your gallbladder drops down as your diaphragm moves during a breath, pressing the inflamed organ against the examiner’s fingers.
Your doctor will also check for tenderness that rebounds when pressure is released, which can signal that inflammatory fluid is irritating the lining of your abdominal cavity. Fever, nausea, and pain that radiates to your right shoulder blade all help paint the clinical picture before any imaging is ordered.
Ultrasound: The First-Line Imaging Test
A standard abdominal ultrasound is nearly always the first imaging test ordered for suspected gallstones. It’s fast, painless, widely available, and doesn’t involve radiation. You’ll typically be asked to fast for 6 to 8 hours beforehand so your gallbladder is full of bile, which makes stones easier to spot. A technician glides a handheld probe over your upper abdomen, and the sound waves create a real-time image of your gallbladder on a monitor.
Ultrasound picks up gallstones with a pooled sensitivity of 94% and specificity of 93%, meaning it catches the vast majority of stones and rarely gives a false alarm. It can also reveal gallbladder wall thickening, surrounding fluid, and other signs of inflammation that point toward acute cholecystitis rather than stones sitting quietly.
Blood Tests and What They Reveal
Blood work doesn’t detect gallstones directly, but it tells your doctor whether a stone has caused a blockage or triggered inflammation. Several markers matter here.
Alkaline phosphatase (ALP), a liver enzyme, rises to four or more times its normal level within one to two days of a bile duct obstruction, regardless of where the blockage sits. Another enzyme called GGT is even more sensitive for detecting bile flow problems and is often checked alongside ALP to confirm that the elevation is coming from the biliary system rather than bone or other tissues.
Bilirubin, the pigment that makes bile yellow, builds up in the blood when a stone blocks its drainage path. Elevated bilirubin combined with abnormal liver enzymes strongly suggests a stone has moved out of the gallbladder and into one of the bile ducts. A complete blood count showing elevated white blood cells adds evidence of infection or inflammation. Together, these results help your doctor decide whether you need basic monitoring or urgent intervention.
When Ultrasound Isn’t Enough
Ultrasound excels at finding stones inside the gallbladder but struggles to see the full length of the bile ducts, especially the lower portion near the intestine. If blood tests suggest a duct blockage but ultrasound doesn’t show one, your doctor will move to more specialized imaging.
MRCP
Magnetic resonance cholangiopancreatography (MRCP) is a specialized MRI that creates detailed images of the bile ducts and pancreatic duct without any needles, dye injections, or sedation. For stones lodged in the common bile duct, MRCP has a sensitivity between 88% and 100% and a specificity between 88% and 92%. It performs comparably to the more invasive alternative (ERCP) for diagnosis and is now the preferred noninvasive option when duct stones are suspected.
Endoscopic Ultrasound
Endoscopic ultrasound (EUS) places a tiny ultrasound probe at the tip of a thin, flexible scope that’s passed through your mouth and into the upper part of your small intestine. Because the probe sits just millimeters from the bile duct, it can detect very small stones and sludge, sometimes called microlithiasis, that standard ultrasound and even MRCP can miss. EUS is recommended when small common bile duct stones are suspected but haven’t shown up on other tests.
HIDA Scan
A HIDA scan evaluates how well your gallbladder functions rather than looking for stones themselves. A small amount of radioactive tracer is injected into a vein, travels through your liver, and collects in your gallbladder. A camera then tracks how much of the tracer your gallbladder squeezes out when stimulated. A normal ejection fraction is above 30% to 35%. If yours falls below that threshold and you have typical gallbladder symptoms but no visible stones, you may be diagnosed with biliary dyskinesia, a motility problem that can cause pain similar to gallstones.
Why CT Scans Often Miss Gallstones
You might assume a CT scan would catch everything, but its sensitivity for gallstones is only about 75%. The reason comes down to stone composition. Gallstones that contain calcium show up well on CT because they’re dense enough to stand out. Cholesterol stones, which account for the majority of gallstones, can have the same density as the surrounding bile, making them essentially invisible on a CT image. This is why ultrasound, not CT, remains the go-to test. CT scans are more useful when your doctor suspects complications like a gallbladder perforation, abscess, or when the diagnosis is uncertain and other abdominal conditions need to be ruled out.
Conditions That Mimic Gallstones
Several conditions can produce upper abdominal pain that feels a lot like gallstone attacks. Peptic ulcers, acid reflux, pancreatitis, and even irritable bowel syndrome share overlapping symptoms. Less obvious mimics include esophageal spasm, pneumonia in the lower right lung, and cardiac chest pain. This overlap is part of why diagnosis involves multiple tools rather than a single test. If your ultrasound comes back clean but your symptoms persist, your doctor may pursue testing for these alternatives before concluding that your gallbladder is the source.