What blood tests are used to diagnose carcinoid tumors?

Blood Tests for Diagnosing Carcinoid Tumors

Chromogranin A (CgA) and 24-hour urinary 5-hydroxyindoleacetic acid (5-HIAA) are the primary blood tests used to diagnose carcinoid tumors, with CgA serving as a general marker for all neuroendocrine tumors and 5-HIAA specifically for carcinoid syndrome. 1, 2

Primary Diagnostic Tests

General Markers

• Chromogranin A (CgA):
  • First-line blood test for all neuroendocrine tumors
  • Produced in large quantities by neuroendocrine cells
  • Elevated in most carcinoid cases, particularly with metastatic disease
  • Can be used for both diagnosis and monitoring disease progression 1, 2

Syndrome-Specific Tests

• 24-hour urinary 5-HIAA:
  • Specific for carcinoid syndrome
  • Metabolite of serotonin produced by carcinoid tumors
  • Varies by tumor location:
    • Midgut carcinoids: Usually elevated (70% of patients)
    • Foregut carcinoids: Sometimes elevated
    • Hindgut carcinoids: Typically not elevated 1, 2

Additional Biochemical Tests

Tumor-Specific Markers

• Tachykinins (neurokinin A and B):

  • Elevated in midgut carcinoids 1

• Whole blood serotonin:

  • Can be useful but less commonly used clinically
  • Levels vary with time of day and meals
  • May remain elevated despite treatment 3

General Screening Tests

• Thyroid function tests (TFTs)
• Parathyroid hormone (PTH)
• Serum calcium
• Calcitonin
• Prolactin
• Alpha-fetoprotein (AFP)
• Carcinoembryonic antigen (CEA)
• Beta-human chorionic gonadotropin (β-HCG) 1

Collection and Testing Considerations

For 5-HIAA Testing

• Potential false positives: Avoid these foods/medications 24 hours before collection:

  • Foods: Bananas, avocados, aubergines, pineapples, plums, walnuts
  • Medications: Paracetamol, fluorouracil, methysergide, naproxen, caffeine 1

• Potential false negatives from:

  • Levodopa, aspirin, ACTH, methyldopa, phenothiazines 1

For CgA Testing

• Blood sample collection:
  • 10 ml standard heparin bottle with trasylol (aprotinin)
  • Must be spun immediately before freezing
  • Send to specialized reference laboratories 1

Testing Algorithm

1. Initial suspicion of carcinoid tumor:

   • Order baseline CgA and 24-hour urinary 5-HIAA 1, 2

2. If carcinoid syndrome suspected:

   • Add specific tests based on suspected syndrome (see table below)

3. If results are equivocal but suspicion remains high:

   • Consider imaging studies (multiphase CT/MRI and somatostatin receptor scintigraphy) 2

4. For monitoring after diagnosis:

   • Measure CgA and 5-HIAA every 3-6 months 2

Syndrome-Specific Testing Guide

Tumor Location	Primary Test	Expected Result
Foregut carcinoid	24h urinary 5-HIAA	Sometimes raised
Midgut carcinoid	24h urinary 5-HIAA + Tachykinins	Usually raised (70%)
Hindgut carcinoid	CgA (general markers)	5-HIAA not raised

Important Caveats

• Diagnostic accuracy: No single test is 100% sensitive or specific; combining biochemical testing with imaging yields the best results 4
• Platelet saturation: Blood serotonin may remain elevated despite treatment due to platelet saturation 3
• Treatment effects: Somatostatin analogs can affect test results, with treated patients showing different biomarker patterns than untreated patients 5
• Definitive diagnosis: While blood tests are valuable, histological confirmation remains the gold standard 1

Remember that a multidisciplinary approach involving specialists in gastroenterology, oncology, endocrinology, radiology, nuclear medicine, and pathology is essential for proper diagnosis and management of carcinoid tumors 1, 6.