What is the diagnostic approach for gastroparesis?

Diagnostic Approach for Gastroparesis

Gastroparesis diagnosis requires three mandatory components: appropriate symptoms (nausea, vomiting, postprandial fullness), documented delayed gastric emptying on 4-hour gastric emptying scintigraphy, and exclusion of mechanical obstruction via upper endoscopy. 1

Step 1: Clinical Assessment

Evaluate for cardinal symptoms that distinguish gastroparesis from other upper GI disorders:

• Nausea and vomiting (particularly of undigested food)
• Early satiety and postprandial fullness
• Bloating and upper abdominal pain 2, 1

Identify high-risk etiologies:

• Diabetes mellitus (present in 25% of all gastroparesis cases; affects 20-40% of patients with long-standing type 1 diabetes) 3
• Post-surgical (especially after gastric, bariatric, or transplant surgery) 3
• Medication-induced (opioids, anticholinergics, GLP-1 agonists—all delay gastric emptying) 3
• Post-viral illness or idiopathic causes 2

Step 2: Exclude Mechanical Obstruction

Perform upper endoscopy (EGD) first to rule out structural lesions including peptic ulcer disease, malignancy, strictures, or inflammatory conditions before proceeding with any functional testing. 1 This is non-negotiable—gastroparesis cannot be diagnosed if mechanical obstruction is present. 2

Step 3: Document Delayed Gastric Emptying

Gold Standard Test

Order 4-hour gastric emptying scintigraphy using a standardized low-fat, radiolabeled solid meal (99mTc sulfur colloid cooked into egg whites, consumed with jam and toast). 4, 1

Critical testing parameters:

• Test duration must be 4 hours—shorter durations (<2 hours) miss approximately 25% of gastroparesis cases 4
• Gastroparesis is confirmed when gastric retention is >10% at 4 hours 4
• For patients being considered for advanced therapies (gastric electrical stimulation, G-POEM), require retention >20% at 4 hours 4

Pre-Test Preparation (Essential to Avoid False Results)

• Withdraw all medications affecting gastric emptying for 48-72 hours (prokinetics, opioids, anticholinergics, GLP-1 agonists) 4
• In diabetic patients, monitor and control blood glucose during testing—hyperglycemia itself slows gastric emptying and produces false-positive results 4, 3
• Avoid smoking on test day 4

Alternative Testing When Scintigraphy Unavailable

13C-octanoate breath testing is a validated non-radioactive alternative that correlates well with scintigraphy. 4, 1 This uses stable isotope labeling and measures 13CO2 in breath samples to indirectly determine gastric emptying. 2

Step 4: Additional Testing for Persistent Symptoms Despite Normal Emptying

Antroduodenal manometry should be reserved for specific scenarios: 4

• Symptoms persist despite normal gastric emptying on scintigraphy
• Need to differentiate neuropathic versus myopathic motility disorders
• Suspicion for small bowel obstruction or rumination syndrome

This test evaluates gastric-duodenal motor coordination and shows decreased antral contractility in gastroparesis. 2, 4

Common Diagnostic Pitfalls to Avoid

• Never diagnose gastroparesis based solely on symptoms or endoscopic findings (e.g., retained food in stomach)—objective delayed emptying must be documented 4, 1
• Do not use 2-hour or shorter gastric emptying studies—they miss 25% of true cases 4
• Failure to control hyperglycemia during testing generates false-positive results in diabetic patients 4, 3
• Not withdrawing gastric motility-affecting medications before testing leads to inaccurate results 4
• Symptom severity does not correlate with degree of gastric emptying delay—do not use clinical severity to infer physiological severity 4

Diagnostic Algorithm Summary

1. Upper endoscopy → exclude mechanical obstruction 1
2. 4-hour gastric emptying scintigraphy with proper preparation → document delayed emptying 4, 1
3. If scintigraphy unavailable → use 13C-octanoate breath testing 4, 1
4. If emptying normal but symptoms persist → consider antroduodenal manometry 4