What is a gastric emptying study?

What is a Gastric Emptying Study?

A gastric emptying study is a diagnostic test that measures how quickly food leaves the stomach, with gastric emptying scintigraphy using a radiolabeled solid meal being the gold standard method that should be performed for at least 2 hours (preferably 4 hours) after meal ingestion. 1, 2

Primary Testing Method: Gastric Emptying Scintigraphy

Gastric emptying scintigraphy is the most widely accepted and reliable diagnostic test for gastroparesis. 1, 2 The procedure involves:

• Patient ingests a bland meal containing a small amount of radioactive material (typically 99mTc-sulfur colloid-labeled egg meal) 1
• Serial imaging is performed at hourly intervals to measure the rate at which the stomach empties 1
• The radionuclide must be cooked into the solid portion of the meal for accurate results 1

Test Duration Considerations

The test should be performed for at least 2 hours, but extending to 4 hours significantly increases diagnostic yield. 1, 2 This is critical because:

• Conventional 2-hour testing misses approximately 25% of patients with delayed gastric emptying 3
• Extending the study from 2 to 4 hours increases detection of gastroparesis from 33% to 58% of symptomatic patients 3
• Shorter test durations are inaccurate for determining gastroparesis 1

Alternative Testing Methods

While scintigraphy remains the gold standard, several alternative methods exist 1:

Breath Testing

• Uses non-radioactive 13C-octanoate labeled into a solid meal 1, 2
• Measures 13C in breath samples to indirectly determine gastric emptying 1
• Primarily used for clinical research and pharmaceutical studies rather than routine clinical practice 1

Ultrasound Imaging

• Increasingly reproducible and less invasive than scintigraphy 1
• Measures changes in cross-sectional area of the gastric antrum 4
• May have investigator variability as a limitation 1

Magnetic Resonance Imaging (MRI)

• Provides reproducible, non-invasive assessment of gastric content volume 1
• Can track serial changes in gastric volume after meal ingestion 1

Antroduodenal Manometry

• Provides information about coordination of gastric and duodenal motor function 1, 2
• Can differentiate between neuropathic and myopathic motility disorders 1, 2
• Useful when scintigraphy results are normal but symptoms persist 1

Less Reliable Methods

• Nasogastric tube aspiration is the least reliable method and should be avoided 1
• Pharmacokinetic studies using water-soluble substances (e.g., paracetamol) absorbed in proximal intestines are available but less commonly used 1

Physiological Principles

Understanding gastric emptying kinetics is essential for interpreting results 1:

• Solid food empties at a constant rate (zero-order kinetics), meaning a very large meal can take more than 8 hours to completely empty 1
• Clear fluids empty exponentially (first-order kinetics), with typical half-life of 10-15 minutes 1
• A 200 mL drink of water reduces to approximately 25 mL within 30 minutes 1

Clinical Applications

Gastric emptying studies are primarily used to diagnose gastroparesis and dumping syndrome. 1, 2

For Gastroparesis Diagnosis

• Confirms delayed gastric emptying in patients with nausea, vomiting, and postprandial fullness 1, 2
• Should be performed after upper endoscopy rules out structural causes 2

For Dumping Syndrome

• Can confirm rapid gastric emptying after esophageal, gastric, or bariatric surgery 1
• However, sensitivity and specificity are generally low because rapid emptying occurs immediately after ingestion, a phase not adequately captured in most studies 1
• The 4-hour study duration integrated into a single value (half-emptying time) may neutralize the rapid initial emptying effect 1

Important Caveats

Several factors can affect test accuracy and interpretation:

• Patients with small gastric pouches from bariatric surgery may have difficulty completing the test meal 1
• The test measures only the rate of emptying, not the underlying cause of symptoms 1
• Normal gastric emptying does not exclude a gastric motility disorder—antroduodenal manometry may be needed 1, 2
• Liquid emptying studies may detect gastroparesis missed by solid studies alone, with 32% of patients having delayed liquid emptying despite normal solid emptying 5