Gallstones Diagnosis: Ultrasound, CT, HIDA Scan & Blood Tests
When should you be tested for gallstones?
Testing for gallstones is indicated when a patient has symptoms suggestive of biliary colic (right upper quadrant pain after fatty meals), complications (jaundice, pancreatitis, fever), or when gallstones are incidentally found on imaging for other reasons. Routine screening for asymptomatic people is not recommended.
Ultrasound – the first‑line imaging test
How it works: High‑frequency sound waves create images of the gallbladder and bile ducts.
What it shows:
- Gallstones (bright echoes with acoustic shadowing).
- Gallbladder wall thickening (>4mm – suggests cholecystitis).
- Pericholecystic fluid (inflammation).
- Dilated common bile duct (suggests obstruction).
- Sludge (echogenic, non‑shadowing material).
Sensitivity: >95% for gallstones >2mm. Less sensitive for small stones or microlithiasis.
Advantages: No radiation, cheap, fast, no preparation needed (except fasting 6‑8 hours).
CT scan for gallstones – when it is useful
CT scan is not the first‑line test for gallstones because some cholesterol stones are radiolucent (not visible). However, it is useful in specific situations:
- Complications: Detects acute cholecystitis (gallbladder wall thickening, stranding, pericholecystic fluid), pancreatitis, or bile duct obstruction.
- Alternative diagnosis: Rules out other causes of right upper quadrant pain (appendicitis, kidney stones, liver lesions).
- Calcified stones: Pigment stones and calcium carbonate stones are visible; some cholesterol stones are not.
Sensitivity: 60‑80% for gallstones (lower than ultrasound).
HIDA scan – for gallbladder function
A HIDA (hepatobiliary iminodiacetic acid) scan is used when acute cholecystitis is suspected but ultrasound is inconclusive, or to diagnose biliary dyskinesia (gallbladder motility disorder without stones).
How it works: A radioactive tracer is injected intravenously, taken up by the liver, and excreted into bile. Serial images track bile flow into the gallbladder and duodenum.
Findings:
- Non‑visualisation of the gallbladder at 4 hours: Indicates cystic duct obstruction – highly sensitive for acute cholecystitis.
- Delayed gallbladder emptying (ejection fraction <35%): Suggests biliary dyskinesia (chronic acalculous gallbladder disease).
Preparation: Fast for 4‑6 hours.
Blood tests – liver function, CBC, bilirubin
Blood tests do not diagnose gallstones directly but help identify complications:
- Liver function tests (LFTs): Elevated alkaline phosphatase (ALP), gamma‑glutamyl transferase (GGT), and bilirubin suggest common bile duct obstruction. Elevated ALT/AST may indicate cholecystitis or pancreatitis.
- Complete blood count (CBC): Elevated white blood cells suggest acute cholecystitis or cholangitis.
- Bilirubin (direct and indirect): Direct hyperbilirubinaemia indicates bile duct obstruction; indirect suggests haemolysis (pigment stones).
- Amylase and lipase: Elevated in gallstone pancreatitis.
Endoscopic ultrasound (EUS) and ERCP
Endoscopic ultrasound (EUS): A specialised ultrasound probe passed through the oesophagus and stomach to image the biliary tree. Highly sensitive for microlithiasis (small stones not seen on standard ultrasound) and common bile duct stones. Used when there is high suspicion for stones with negative imaging.
ERCP (endoscopic retrograde cholangiopancreatography): Both diagnostic and therapeutic. A camera is passed into the duodenum, and dye is injected into the bile duct. Can remove stones, place stents, and perform sphincterotomy. Used for confirmed or high‑suspicion CBD stones, especially with jaundice or pancreatitis.
Interactive FAQ – Gallstones diagnosis
Yes – small stones (<2mm) or microlithiasis can be missed. Sludge may be mistaken for stones. EUS is more sensitive for microlithiasis.
Endoscopic ultrasound (EUS) and MRCP (magnetic resonance cholangiopancreatography) are the most sensitive non‑invasive tests. ERCP is the gold standard for diagnosis and treatment.
Yes – fasting for 6‑8 hours ensures the gallbladder is distended and not contracted, which improves visualisation of stones and wall thickness.
No blood test diagnoses gallstones directly. Elevated bilirubin, alkaline phosphatase, or white blood cells suggest complications (obstruction or infection).
Yes – up to 40% of cholesterol stones are radiolucent and not visible on CT. Ultrasound is preferred for diagnosis.
It diagnoses acute cholecystitis (non‑visualisation of gallbladder) and biliary dyskinesia (low ejection fraction). It does not directly show stones.
Elevated lipase/amylase + imaging (CT or ultrasound) showing gallstones + no other cause of pancreatitis. ERCP is often performed to remove the stone.
MRCP (magnetic resonance cholangiopancreatography) is used to visualise the bile duct when CBD stones are suspected, especially when EUS is unavailable. It does not require contrast and has no radiation.
No – clinical history alone is not sufficient. Imaging (ultrasound) is required to confirm the diagnosis.
Disclaimer: This information is for educational purposes. If you have symptoms of gallstones, consult a gastroenterologist at Vivekananda Hospital for appropriate diagnostic testing.