How are neuroendocrine tumors diagnosed?
Required laboratory tests vary depending on tumor location and patient complaints. Two common tests are testing for chromogranin A levels in the blood (Chromogranin A CgA) and collecting urine for 5 HIAA (5-hydroxy-indole-acetic acid). These tests may be affected by diet or medication, so care must be taken not to consume certain types of foods and medications before or during the tests, as detailed below.
Chromogenin A level test in the blood
CgA is a glycoprotein (a compound of protein and carbohydrate) produced in neuroendocrine cells, and can therefore be used as a measure of the presence of neuroendocrine tumors and a marker for the extent of the disease. Interpretation of a change in chromogranin A level should be made with caution, and in some cases a change in its level may indicate trends in improvement or progression of the tumor.
Many factors can affect CgA – heart disease, kidney disease, inflammatory diseases, medications to protect the stomach lining (proton pump inhibitors) and antihistamines (to treat allergies). It is therefore important to consult a doctor who is an expert in the field when a high level of CgA is obtained.
It is recommended to perform the test two to three weeks after stopping to take proton pump inhibitors and at least 72 hours after stopping antihistamines.
Urine 5HIAA level test
Neuroendocrine cells may secrete serotonin, one of the breakdown products in the body of which is 5HIAA (hydroxyindolic acid). The acid level can be measured by 24-hour urine collection and thus a measure of disease progression or response to treatment, as well as the effect on various organs may be obtained.
However, high levels of 5HIAA can be due to reasons unrelated to neuroendocrine tumors, such as a diet rich in serotonin or tryptophan (the amino acid from which serotonin is produced). Therefore, for at least 48 hours before and during the collection of urine, foods containing serotonin or tryptophan should be avoided: fruits (especially banana, pineapple, grapefruit, dates, plum, kiwi and tomato and its products), nuts (especially walnuts and pecans), eggplant and avocado. Also, before taking the test, avoid taking medications that affect the levels of serotonin in the urine, including certain types of painkillers, cough syrup, muscle relaxants and antidepressants.