Management of Diarrhea with Elevated Serum Chromogranin A

Initial Diagnostic Workup

The National Comprehensive Cancer Network recommends excluding false positives by confirming the patient is not taking proton pump inhibitors and does not have renal failure, liver failure, hypertension, or chronic gastritis, then proceeding with multiphasic CT or MRI imaging of the abdomen and pelvis to localize a suspected neuroendocrine tumor 1, 2
Discontinue proton pump inhibitors for at least 1 week before interpreting chromogranin A results, as these medications are a common cause of false elevation 1, 2, 3
Assess renal function, as renal failure causes spurious elevation 1, 2, 4
Evaluate liver function, as hepatic failure elevates chromogranin A independently of neuroendocrine tumors 1, 2, 4
Check blood pressure, as hypertension alone can increase levels 1, 2, 4

Obtain multiphasic CT or MRI scan of the abdomen and pelvis as the initial imaging modality recommended by the National Comprehensive Cancer Network 1, 2, 5
Follow with somatostatin receptor scintigraphy (Octreoscan) to detect tumors that may be missed by CT/MRI 5
Consider endoscopic ultrasound (EUS), particularly for small pancreatic lesions 1, 4

For Gastrinoma (Diarrhea with Dyspepsia/Ulcer Symptoms): Measure fasting serum gastrin levels after discontinuing proton pump inhibitors for at least 1 week 1, 2, 4
For VIPoma (Watery Diarrhea, Hypokalemia, Achlorhydria): Measure serum vasoactive intestinal polypeptide (VIP) levels 1, 2
For Insulinoma: Check fasting insulin, C-peptide, and proinsulin; consider 48-72 hour observed fast 1, 4

24-hour urinary 5-hydroxyindoleacetic acid (5-HIAA) for serotonin-producing carcinoids, particularly with carcinoid syndrome features 5
Patients must avoid foods that increase 5-HIAA (avocados, bananas, coffee) for 48 hours before collection 5
Pancreatic polypeptide (PP) for nonfunctioning pancreatic NETs (category 3 evidence) 1, 2

Chromogranin A levels ≥2 times the upper limit of normal are associated with shorter survival in metastatic NETs (HR 2.8; 95% CI 1.9-4.0; P<0.001) 1, 6
Elevated levels correlate with tumor volume 1, 6
Chromogranin A is prognostic in patients treated with everolimus 1, 6

Do not interpret elevated chromogranin A while the patient is on proton pump inhibitors - this is the most common cause of false positives 1, 2, 4
Do not assume rising chromogranin A in an asymptomatic patient with stable imaging requires new therapy 5, 6
Be aware that chromogranin A is elevated in only 60% of neuroendocrine tumors, so a normal level does not exclude the diagnosis 1, 2, 4, 7

Somatostatin receptor scintigraphy (Octreoscan) should be used as a secondary functional imaging study when multiphasic CT or MRI of the abdomen and pelvis is negative or equivocal, because about 80 % of neuroendocrine tumors express somatostatin receptors, allowing detection of lesions missed by conventional imaging. 8

24‑hour urinary 5‑hydroxyindoleacetic acid (5‑HIAA) is the preferred test for confirming mid‑gut carcinoid tumors in patients presenting with carcinoid‑related symptoms (e.g., flushing, presyncope). 9

Patients must avoid specific foods and substances (including avocados, bananas, cantaloupe, eggplant, pineapples, plums, tomatoes, hickory nuts, plantains, kiwi, dates, grapefruit, honeydew, walnuts, coffee, alcohol, and smoking) for 48 hours before and during urine collection to prevent dietary interference and false‑positive 5‑HIAA results. 10