From the Guidelines
Diagnosing carcinoid tumors requires a combination of laboratory tests, including a 24-hour urine collection for 5-hydroxyindoleacetic acid (5-HIAA) and blood tests for chromogranin A (CgA) and specific hormone levels, as well as imaging studies like CT scans, MRI, and somatostatin receptor scintigraphy. The most important laboratory test is the 24-hour urine collection for 5-HIAA, which measures the breakdown product of serotonin often produced by carcinoid tumors 1. Blood tests should include chromogranin A (CgA), which is elevated in most carcinoid patients, and specific hormone levels such as serotonin, gastrin, and substance P depending on symptoms 1. Additional useful tests include neuron-specific enolase (NSE) and pancreastatin. These biochemical markers should be complemented by imaging studies like CT scans, MRI, somatostatin receptor scintigraphy (Octreoscan), or gallium-68 DOTATATE PET scans, which are particularly sensitive for detecting carcinoid tumors 1. It's essential to note that certain foods (like walnuts, bananas, avocados) and medications (including SSRIs and certain blood pressure medications) can interfere with 5-HIAA results, so these should be avoided before testing 1. For accurate diagnosis, these tests should be ordered in conjunction with a thorough clinical evaluation of symptoms such as flushing, diarrhea, wheezing, and abdominal pain that might suggest carcinoid syndrome. Some key points to consider when evaluating patients with suspected carcinoid tumors include:
- Using multiphase CT or MRI scans to evaluate liver metastasis and chest CT to assess for lung metastases 1
- Considering radiolabeled somatostatin receptor scintigraphy, such as [111In-DTPA]-octreotide, in the initial evaluation of patients with NETs 1
- Avoiding certain foods and medications that can interfere with 5-HIAA results, such as avocados, bananas, and SSRIs 1
- Using chromogranin A as a tumor marker, although it is not diagnostic and can be elevated in several concurrent medical conditions 1
From the Research
Laboratory Tests for Diagnosing Carcinoid Tumors
The diagnosis of carcinoid tumors (neuroendocrine tumors) involves various laboratory tests, including:
- Biochemical markers, such as urinary 5-HIAA or an elevated serotonin level in plasma, which help establish the diagnosis of GI carcinoid 2
- Plasma chromogranin A, although it has poor specificity (68%) and its level depends on disease involvement and therapeutic response 2
- Neuroendocrine markers, including urinary 5-Hydroxyindoleacetic acid (5-HIAA) and serum Chromogranin-A (CgA) 3
Imaging Techniques
Imaging techniques used to diagnose and localize carcinoid tumors include:
- Octreoscan, which is the best imaging technique to detect GI carcinoids 2
- CT scan and MRI, which are superior for the detection of metastasis 2
- 18F-DOPA or 11C-5-HTP/PET, which improve the results of metabolic imaging 2
- Somatostatin receptor scintigraphy (SRS), which can be used for detection and staging of carcinoid tumors 4
- Positron emission tomography (PET), which has been reported to have high tracer uptake in patients with carcinoid tumors 4
- MIBG, which has been used for decades to visualize carcinoid tumors 4
Endoscopic Procedures
Endoscopic procedures used to diagnose carcinoid tumors include:
- Upper endoscopy or colonoscopy, which can be performed to detect foregut carcinoid in MEN, or hindgut carcinoid 2
- Echoendoscopy, which visualizes abdominal wall and local node involvement 2
- Enteroscopy and capsule endoscopy, which can localize midgut carcinoids 2
- Endoscopic ultrasound investigations, which might be relevant for diagnosis of duodenal carcinoids 5