Indications for Testing

Carcinoid syndrome marked by symptoms of flushing and diarrhea, wheezing, right-sided congestive heart failure

Laboratory Testing

  • Symptoms should guide laboratory testing for biochemical markers (National Comprehensive Cancer Network [NCCN], 2017)
  • Testing for hormones produced by NETs may include
    • 5-hydroxyindoleacetic acid (5-HIAA) (urine or plasma) – for flushing
      • Metabolic product of serotonin
      • Two sequential 24-hour urine samples recommended
      • Significant elevation (10 times the upper reference limit) of urine 5-HIAA may indicate the presence of a carcinoid tumor
    • Chromogranin A
      • Prognostic marker in NETs; elevated levels suggest poorer prognosis (NCCN, 2017)
    • Gastrin – fasting concentrations, with individual off proton-pump inhibitors for 1 week
      • Prognostic marker in gastric tumors with hypergastrinemia syndrome
    • Adrenocorticotropic hormone (ACTH)/cortisol – useful in thymic and bronchial tumors with Cushing syndrome
    • Serotonin – whole blood preferred over serum
      • Highly specific for carcinoid identification
      • Not frequently used
    • Neurokinin A – prognostic marker for midgut NETs


  • Definitive diagnosis requires biopsy and pathologist examination
  • Useful immunohistochemical stains may include chromogranin A, synaptophysin, and cytokeratin 8,18
  • For detailed descriptions, refer to ARUP’s Immunohistochemistry Stain Offerings

Imaging Studies

  • Computed tomography (CT)/magnetic resonance imaging (MRI)
    • Abdomen and pelvis
  • Echocardiography
    • For bronchopulmonary effects
    • Evaluate valvular thickening and leaflet damage
  • Endoscopy
    • As indicated by location (esophagogastroduodenoscopy [EGD], colonoscopy)
  • Other imaging as indicated
    • Bronchoscopy
    • CT of chest
    • CT enterography or capsule endoscopy
    • Endorectal MRI
    • Endoscopic ultrasound
    • Fluorodeoxyglucose positron emission tomography (FDG-PET)/CT and brain imaging with CT/MRI for poorly differentiated carcinomas
    • MRI with gadoxetate
    • Somatostatin receptor-based imaging

Differential Diagnosis