Neuroendocrine and endocrine markers: a complete guide for patients (Calcitonin, Chromogranin A, 5-HIAA and Metanephrines)

Have you had tests and seen elevated values such as “calcitonin”, “chromogranin A”, “5-HIAA” or “metanephrine” and don’t understand what they mean? These tests seem complicated, but behind them lies a simple principle: some tumors (called neuroendocrine) produce excess hormones, and these hormones can be measured in the blood or urine. But remember the basic principle valid in 2026: tumor markers are not used for screening in healthy people and, taken individually, do not make a diagnosis. This guide explains, in a way that everyone can understand, what each marker means and how it guides medical decisions.

1. What are neuroendocrine tumors?

The neuroendocrine system is made up of special cells, spread throughout the body (thyroid, pancreas, intestine, adrenal glands), that produce hormones. When these cells form a tumor, they can continue to “manufacture” hormones in large quantities — hence the characteristic symptoms (flushing, diarrhea, hypertension).

These tumors also produce “marker” substances that can be measured. There are two major general markers (Chromogranin A and NSE), plus specific markers for each type of hormone. Let’s take them one by one.

2. Chromogranin A: the “universal” marker of neuroendocrine tumors

Chromogranin A (CgA) is a protein secreted by almost all neuroendocrine cells, regardless of location. Therefore, it is considered a general marker for neuroendocrine tumors (NETs). The normal value is below 100 ng/mL.

Here is how the values are interpreted:

CgA value	Possible meaning
<100 ng/mL	Normal; active tumor unlikely
100–500 ng/mL	Suggestive of NET; requires imaging
500–1,000 ng/mL	Moderate–significant tumor volume
>1,000 ng/mL	Large tumor volume, poorer prognosis

Chromogranin A is elevated in 60–90% of neuroendocrine tumors. The baseline value correlates with tumor volume, and a decrease of more than 50% after treatment indicates a good response.

Beware of a key pitfall: Chromogranin A may be falsely elevated in patients taking antacid medications (proton pump inhibitors, such as omeprazole). Ideally, these medications should be discontinued about a week before the test. Other benign causes include atrophic gastritis, renal failure, and hypertension.

3. Calcitonin: the marker of medullary thyroid cancer

Calcitonin is a hormone produced by the C cells of the thyroid. It is the main marker for medullary thyroid cancer (MTC) . Normal values are below 5 pg/mL in women and below 8.4 pg/mL in men.

Interpretation of values:

• 10–100 pg/mL – requires retesting and imaging
• >100 pg/mL – highly suspicious for medullary thyroid cancer
• >500 pg/mL – indicates metastatic disease in most cases

Calcitonin is present in 90–95% of patients with MTC at diagnosis. A particularly valuable aspect is the calcitonin doubling time (CDT) , which predicts the aggressiveness of the disease:

• CDT under 1 year → aggressive disease, median survival 2–3 years
• CDT over 2 years → indolent disease, median survival over 10 years

After surgical removal of the thyroid, calcitonin should become undetectable—its normalization is associated with excellent long-term survival. A new increase may signal recurrence 6–12 months before imaging.

Genetic link: RET gene mutations are present in 100% of patients with familial forms (MEN 2A, MEN 2B) and in 50% of apparently sporadic cases. Therefore, RET testing guides the decision for prophylactic thyroidectomy in family members. Calcitonin is often monitored in conjunction with CEA.

4. 5-HIAA: marker of carcinoid syndrome

Some neuroendocrine tumors (called carcinoids) produce excess serotonin , causing “carcinoid syndrome”: flushing, diarrhea, and bronchospasm. Serotonin is converted in the body into a metabolite called 5-HIAA (5-hydroxyindoleacetic acid) , which is measured in urine collected over 24 hours. The normal value is below 8 mg/24h.

Interpretation of values:

• 8–20 mg/24h – borderline increase, requires clinical correlation
• >20 mg/24h – diagnosis of carcinoid syndrome
• >100 mg/24h – significant tumor volume, serotonin producer

Pay attention to a crucial dietary detail: 5-HIAA can be falsely elevated by foods rich in serotonin, such as bananas, tomatoes, pineapple, chocolate, and nuts. Therefore, patients should avoid these foods 48–72 hours before urine collection for accurate results. Some medications (SSRI antidepressants) can also influence the result.

5. Metanephrines: pheochromocytoma marker

Pheochromocytoma is a tumor of the adrenal glands that produces excess catecholamines (adrenaline, noradrenaline), causing hypertension, headaches, and palpitations. It is best detected by measuring metanephrines —stable metabolites of catecholamines.

The preferred test is the measurement of plasma free metanephrines , the most sensitive assay (96–99% sensitivity). Alternatively, 24-hour urine metanephrines can be measured (normal <400 µg/24h).

Interpretation:

• Normal metanephrines → pheochromocytoma very unlikely
• Increased metanephrines → suspicion; imaging (CT/MRI) is recommended
• Very high values (>4× normal limit) → diagnosis in appropriate clinical context

Beware of pitfalls: plasma collection should be done in a supine position, after 30 minutes of rest, to avoid false positive results. Numerous medications (tricyclic antidepressants, decongestants), stress, caffeine and tobacco can falsely increase values – ideally, interfering medications are discontinued one week beforehand. And in pheochromocytoma, Chromogranin A is increased in 90% of cases, supporting the diagnosis. Genetic testing (SDHB, VHL, RET mutations) is recommended for all patients.

6. Other specific hormonal markers

When a neuroendocrine tumor produces a certain hormone, doctors dose the corresponding marker:

• Gastrin – elevated in gastrinoma (Zollinger-Ellison syndrome); a value above 1,000 pg/mL is diagnostic.
• Insulin and C-peptide – useful for insulinoma, which causes recurrent hypoglycemia.
• VIP – increased in VIPom (severe watery diarrhea, hypokalemia); values above 200 pg/mL are diagnostic.
• Glucagon – elevated in glucagonoma (characteristic skin rash, diabetes); values above 500 pg/mL.
• NSE (neuron-specific enolase) – secondary marker, increased especially in high-grade neuroendocrine tumors.

7. Three golden rules for interpretation

1. Markers are not used for screening in healthy individuals; they complement imaging and biopsy.
2. Correct harvesting is essential: antacids falsify Chromogranin A, serotonin-rich foods falsify 5-HIAA, and position and medication influence metanephrines.
3. The trend over time (increase or decrease in repeated measurements) is more relevant than a single isolated value.

NEUROENDOCRINE and ENDOCRINE tumor markers

🔬 Tumor / Location	🎯 Main marker	📊 Normal value	🔎 Growth meaning
Thyroid (Medullary Thyroid Cancer MTC)	Calcitonin	<5 pg/mL (F) / <8.4 pg/mL (B)	>100 pg/mL = suspected MTC; >500 pg/mL = metastatic disease
Neuroendocrine tumors (general)	Chromogranin A	<100 ng/mL	100–500 = probable NET; >1,000 = large tumor volume, poor prognosis
Carcinoid (small intestine)	5-HIAA (24h urine)	<8–10 mg/24h	>20 mg/24h = active carcinoid syndrome; correlated with elevated serotonin
Adrenal (pheochromocytoma)	Metanephrines (plasma/urine)	Plasma <0.46 nmol/L; urine <400 µg/24h	>4× cutoff = pheochromocytoma; sensitivity 96–99%
Lung (SCLC, carcinoid)	NSE + ProGRP	NSE <12.5 ng/mL; ProGRP <50 pg/mL	>25 ng/mL (NSE) = SCLC; ProGRP increased = expansion

💡 Specific “hormonally active” markers: for gastrinoma , gastrin is measured (>1,000 pg/mL)

; for insulinoma – insulin + C-peptide

; for VIPom – VIP (>75 pg/mL, watery diarrhea)

; for glucagonoma – glucagon (>500 pg/mL)

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⚠ Sampling pitfalls (essential!): • Chromogranin A is falsely elevated in patients taking antacids (proton pump inhibitors) — ideally discontinued ~1 week prior

• 5-HIAA is falsely increased by foods rich in serotonin (bananas, tomatoes, pineapple, chocolate, nuts) — avoid 48–72h before

• Plasma metanephrines are collected in the supine position, after 30 min of rest ; medications, caffeine and tobacco give false positives

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🧬 Genetic links: RET mutations are present in 100% of familial forms of MTC (MEN 2A/2B) and guide prophylactic thyroidectomy

SDHB, VHL, RET mutations are recommended to be tested in all patients with pheochromocytoma

How Artificial Intelligence helps you correctly interpret neuroendocrine markers

As you have seen, neuroendocrine tumors harbor a multitude of markers (Chromogranin A, calcitonin, 5-HIAA, metanephrines, gastrin, insulin), each with its own thresholds, harvesting pitfalls and genetic correlations (RET, SDHB). Manually correlating all this data with international guidelines is difficult, and treatment protocols are updated from one month to the next.

Oncoexpertai platform comes in . Unlike a simple reading of the analyses, our advanced Artificial Intelligence algorithms instantly scan your entire marker profile and correlate it with thousands of clinical studies and international oncology guidelines updated in real time (NCCN / ESMO). The technology does not replace the doctor, but gives him the certainty that the proposed treatment regimen is the most suitable for your specific profile.

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Disclaimer: The information in this article is for informational and educational purposes only. It is not a substitute for the consultation, diagnosis, or treatment provided by a qualified medical professional. For any decision regarding your health, always consult a medical professional. .

Bibliography

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5. Jensen RT, Cadiot G, Brandi ML, et al. ENETS Consensus Guidelines for the Management of Patients with Digestive Neuroendocrine Neoplasms: Functional Pancreatic Endocrine Tumor Syndromes. Neuroendocrinology. 2012;95(2):98–119. doi: 10.1159/000335591
6. Modlin IM, Gustafsson BI, Moss SF, Pavel M, Tsolakis AV, Kidd M. Chromogranin A—Biological Function and Clinical Utility in Neuroendocrine Tumor Disease. Annals of Surgical Oncology. 2010;17(9):2427–2443. doi: 10.1245/s10434-010-1006-3
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Dr. Onisim Florin Senior Medical Oncologist | Founder of OncoExpertAI

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