Tumour marker tests

Blood samples will be collected for a range of tests. Markers for NETs that may be measured in the blood to give further information to your doctor:

• Chromogranin A (CgA)  – this is the most common circulating tumour marker for NETs. In blood tests, the levels of CgA are higher than normal in 60% to 80% of functional and non-functional gastrointestinal NETs and pancreatic NETs.
• Levels of other tumour markers that are released by functional and hormone-producing NETs in the blood will also be tested. These markers include hormones and peptides, such as somatostatin, pancreatic polypeptide, insulin, gastrin, glucagon, neurotensin and vaso-intestinal peptide (VIP).
• A blood test for 5-HIAA is in development that may replace the 5-HIAA urine test which is currently the gold standard (see below).

Other blood tests for NETs may include:

• Full blood count (FBC).
• Kidney function tests (urea and electrolytes).
• Liver function tests.
• Thyroid function tests.
• Pituitary hormone screen, measuring hormones such as adrenocorticotropic hormone (ACTH), prolactin, growth hormone (GH) and cortisol.
• Serum calcium and parathyroid hormone level tests, for all patients with pancreatic NETs, as a screening test for MEN-1 syndrome.
• NT proBNP– a blood test to check for carcinoid heart disease.
• Measurement of vitamins (e.g. vitamin A, B₁₂, D, and E) and minerals (e.g. iron, selenium,and zinc).
• Pituitary hormone screen, measuring hormones such as adrenocorticotropic hormone (ACTH), prolactin, growth hormone (GH) and cortisol.

5-HIAA is a 24-hour urine test that measures the amount of 5-hydroxyindoleacetic acid (5-HIAA) in the body. 5-HIAA is a substance that is broken down (metabolised) in the body from serotonin by an amino acid called tryptophan.

A high level of 5-HIAA in a 24-hour urine test sample is likely to confirm whether a person’s symptoms, such as flushing of the skin (particularly the face) and diarrhoea, are due to carcinoid syndrome. However, this test may not detect other types of tumours, such as lung NETs as they do not produce 5-HIAA. In these cases, imaging techniques may be used to identify NETs suspected of being in the lungs.

For the 5-HIAA test you will usually be asked to avoid certain foods beforehand and for 24 hours during the test as they contain substances that might artificially raise your 5-HIAA levels and so give a false positive result. These foods include chocolate, olives, bananas, pineapple and its juice; all tomato products, plums, aubergine, avocado, kiwi fruit, walnuts, brazil nuts, cashew nuts, tea, coffee and alcohol. Your NET specialist doctor should be able to advise you on this and provide you with a list.

Catecholamines is a collective term for the hormones adrenaline, noradrenaline and dopamine. High levels of catecholamines or their metabolites in the urine or blood may indicate the presence of NETs. Catecholamines or their metabolites are usually measured in 24-hour urine samples.