February 12, 2024

Can Blood Tests Detect Serotonin Levels?

Can blood tests detect serotonin levels? Yes – this is the most common way to check that. Serotonin levels are usually tested when carcinoid syndrome is suspected and may be conducted through a standard blood sample taken from a vein. Do you wish to learn more about serotonin, the instances in which it should be tested, and how the test works? Then read on.

Key Takeaways

  • Serotonin (5-hydroxytryptamine or 5-HT) is a substance in the human body that transports messages across the nervous system. It is produced from tryptophan, which is an essential amino acid.
  • You can find tryptophan in many foods, such as: salmon, eggs, cheese, nuts.
  • Can blood tests detect serotonin levels? Yes, though they are usually used with other tests, such as urine or brain imaging.
  • High levels of serotonin may indicate carcinoid cancers or come with symptoms such as fever or headache – in the most drastic cases, an overload of serotonin might lead to death.
  • Low serotonin levels are responsible for many mental conditions, from depression and anxiety to phobias, dementia, or even aggression.

You may also be interested in reading our article on melatonin and iron levels.

What Is Serotonin?

Serotonin, or 5-hydroxytryptamine (5-HT), is a monoamine transmitter – a chemical that transports messages between the cells in your brain and body. It impacts learning, memory, and happiness but also vital functions, such as body temperature control, sleep, hunger, or bowel movements. Low serotonin levels may lead to conditions such as depression, anxiety, or mania.

Serotonin is produced mostly in the intestines – according to Zhong et al., 90% of the substance is produced there. While low levels of serotonin might lead to mental conditions, its overload is usually an indicator of carcinoid syndrome, which is a set of symptoms signaling several kinds of tumors. (2021)

What is important about serotonin is that it is made from an essential amino acid – tryptophan. This means that we cannot produce this amino acid in our bodies – we need to get it from food.

What Foods Have Serotonin?

Before we discuss if a blood test can detect serotonin levels, let’s go over the list of the most common foods containing tryptophan. This is useful in case the test points out low serotonin levels.

  • salmon,
  • eggs,
  • cheese,
  • turkey,
  • tofu,
  • pineapples,
  • nuts,
  • supplements and medication.

Can Blood Tests Detect Serotonin Levels?

So, can a blood test detect serotonin levels? Yes! A standard blood sample taken from a vein can be analyzed to detect serotonin levels. Such tests might be required after a urine 5-HIAA test, but typically, they are not utilized to monitor the results of a carcinoid syndrome treatment.

Moreover, when preparing such a test, it is crucial to remember that some foods and medicines may affect the results if consumed before the sample is taken. This is why it is usually a follow-up test used to confirm the results of 5-HIAA.

Often, physicians combine even more tests, adding spinal tap (or lumbar puncture) and brain imaging to the mix. This happens typically when they suspect the serotonin syndrome – an overload of serotonin in the patient’s body.

See our article on hormone test kits.

Conditions Related to High/Low Serotonin Levels

Understanding that blood tests can detect serotonin levels is one thing, but the most crucial piece of knowledge here is related to the conditions that can be caused by lack or overload of serotonin. Why don’t we explore them now?

Low Serotonin Levels

  • depression,
  • anxiety,
  • sleeping disorders,
  • digestive problems,
  • suicidal thoughts,
  • obsessive-compulsive disorder,
  • panic disorders,
  • schizophrenia,
  • phobias,
  • aggression,
  • dementia.

High Serotonin Levels (Serotonin Syndrome)

  • fever,
  • headache,
  • dilated pupils,
  • muscle twitches and spasms,
  • high blood pressure,
  • elevated heart rate.

What Is Carcinoid Syndrome?

When discussing serotonin testing and the symptoms that might come with high/low levels of this chemical, we must mention carcinoid syndrome – a set of symptoms caused by carcinoid tumors. These cancer changes usually start in the digestive tract and may impact:

  • stomach,
  • appendix,
  • small intestine,
  • colon,
  • rectum.

The reason behind these tumors affecting the serotonin levels is pretty simple. Some of such cancer changes are capable of converting tryptophan into serotonin, hence accelerating the process and raising the serotonin levels. This is not only dangerous because it indicates tumors but also because it might lead to other symptoms that are caused purely by serotonin overload.

Can you use blood tests to detect serotonin levels and hence discover the carcinoid tumors? Yes. Therefore, it is crucial to understand the symptoms of carcinoid syndrome:

  • diarrhea,
  • abdominal pain,
  • nausea,
  • rectal bleeding,
  • rectal pain,
  • redness.

We hope that we answered all your questions regarding serotonin levels and how you can detect them with blood tests. We invite you to read our other materials, such as our article on cortisol tests.


Zhong, W., Shahbaz, O., Teskey, G., Beever, A., Kachour, N., Venketaraman, V., & Darmani, N. A. (2021). Mechanisms of Nausea and Vomiting: Current Knowledge and Recent Advances in Intracellular Emetic Signaling Systems. International Journal of Molecular Sciences, 22(11). https://doi.org/10.3390/ijms22115797