Optimal Result: 40 - 91 umol/L.

Tryptophan is involved in serotonin production via vitamin B6-dependent pathways resulting in the intermediate 5-hydroxytryptophan (5-HTP).

5-HTP is often used as a supplement for serotonin formation instead of tryptophan, which can be quickly metabolized in other pathways. Serotonin is further metabolized to melatonin via methylation. Because of these downstream conversions, therapeutic administration of 5-HTP has been shown to be effective for depression, fibromyalgia, binge eating associated with obesity, chronic headaches, and insomnia.

Tryptophan can be alternatively metabolized via the kynurenine pathway to produce various organic acids - kynurenic acid, quinolinic acid, and xanthurenic acid.

Two percent of dietary tryptophan is converted to niacin (vitamin B3) in the liver and deficiencies of vitamin B6, riboflavin, iron, and heme as essential cofactors for enzymes can slow the reaction rate.

Hartnup disease is a rare genetic disorder involving an inborn error of amino acid metabolism with symptoms developing in childhood. The intestines cannot properly absorb neutral amino acids and the kidney cannot properly resorb them. This leads to increased clearance of neutral amino acids in the urine, and normal or low levels in the plasma. Tryptophan deficiency is thought to account for the symptoms, since tryptophan converts to vitamin B3. This B3 deficiency causes dermatitis, a characteristic feature of Hartnup disease.


- Adrych K, Smoczynski M, Stojek M, et al. Decreased serum essential and aromatic amino acids in patients with chronic pancreatitis. World J Gastroenterol. 2010;16(35):4422-4427.

- Birdsall TC. 5-Hydroxytryptophan: a clinically-effective serotonin precursor. Alt Med Review. 1998;3(4):271-280.

- Gasperi V, Sibilano M, Savini I, Catani MV. Niacin in the Central Nervous System: An Update of Biological Aspects and Clinical Applications. Int J Mol Sci. 2019;20(4).

- Patel AB, Prabhu AS. Hartnup disease. Indian journal of dermatology. 2008;53(1):31-32.

- Ciecierega T, Dweikat I, Awar M, Shahrour M, Libdeh BA, Sultan M. Severe persistent unremitting dermatitis, chronic diarrhea and hypoalbuminemia in a child; Hartnup disease in setting of celiac disease. BMC Ped. 2014;14:311.

- NORD. Hartnup Disease. Rare Dis Info 2019, 2020.

- Gulati K, Anand R, Ray A. Nutraceuticals as adaptogens: their role in health and disease. In: Nutraceuticals. Elsevier; 2016:193-205.

- Wolf H, Brown RR. The effect of tryptophan load and vitamin B 6 supplementation on urinary excretion of tryptophan metabolites in human male subjects. Clin Sci. 1971;41(3):237- 248.

- Shibata K. Organ Co-Relationship in Tryptophan Metabolism and Factors That Govern the Biosynthesis of Nicotinamide from Tryptophan. J Nutr Sci Vitaminol. 2018;64(2):90-98.

- Shibata K, Shimada H, Kondo T. Effects of feeding tryptophan-limiting diets on the conversion ratio of tryptophan to niacin in rats. Biosci Biotech Biochem. 1996;60(10):1660-1666.

- Murray MF, Langan M, MacGregor RR. Increased plasma tryptophan in HIV-infected patients treated with pharmacologic doses of nicotinamide. Nutrition. 2001;17(7- 8):654-656.

- Capuron L, Ravaud A, Neveu PJ, Miller AH, Maes M, Dantzer R. Association between decreased serum tryptophan concentrations and depressive symptoms in cancer patients undergoing cytokine therapy. Molec Psych. 2002;7(5):468- 473.

- Ramos-Chavez LA, Roldan-Roldan G, Garcia-Juarez B, et al. Low Serum Tryptophan Levels as an Indicator of Global Cognitive Performance in Nondemented Women over 50 Years of Age. Ox Med Cell Longevity. 2018;2018:8604718.

What does it mean if your Tryptophan result is too low?

Low levels of essential amino acids may indicate a poor-quality diet, or maldigestion due to deficient digestive peptidase activity or pancreatic dysfunction. Because some dietary tryptophan is converted to niacin, tryptophan-deficient diets have been associated with lower niacin production. Intereastingly, niacin administration increased plasma tryptophan by 40%.

Clinically, low serum tryptophan levels have been shown to correlate with depressive symptoms and cognitive impairment.

What does it mean if your Tryptophan result is too high?

Elevated tryptophan may be seen in high protein diets or supplementation. Stress, insulin resistance, magnesium or vitamin B6 deficiency, and increasing age can all inhibit the conversion of tryptophan to 5-HTP and elevate tryptophan. Lack of nutrient cofactors (vitamin B6, riboflavin, iron, and heme) in several other tryptophan pathways can also contribute to elevations.

Lastly, glutaric aciduria is a rare inborn error of metabolism characterized by elevated tryptophan.

10 000+ happy customers
100% satisfaction
★ ★ ★ ★ ★ customer support

Understand blood, stool, and urine medical results from all your laboratories.

Upload Your Personal Results

Upload Personal Results

Monthly plan

Annual plan

Own it for life

  • Subscription
  • Data entry service included

    Data entry service

    Our exclusive data entry service is a convenient way to get your results into your private dashboard. Simply attach an image or a file of your lab test results, and one of our qualified data entry team members will add the results for you. We support all sorts of files, whether PDFs, JPGs, or Excel. This service is excellent whether you have a lot of reports to upload or are too busy to do the data entry yourself.

  • Instant interpretation
  • Use free data entry form

    Free data entry form

    We strive to make the data entry process easy for you. Whether by offering dozens of templates to choose from that pre-populate the most popular laboratory panels or by giving you instant feedback on the entered values. Our data entry forms are an easy, fast, and convenient way to enter the reports yourself. There is no limit on how many lab reports you can upload.

  • 4000+ biomarkers explained
  • Nutrition recommendations
  • Cancel anytime


$15 /month

billed every month

  • monthly
  • $15 per report
  • ✓ Instant interpretations
  • ✓ 4000+ biomarkers explained
  • ✓ Nutrition recommendations
  • ✓ Free data entry form
  • ✓ Unlimited data
  • ✓ $15 data entry service
  • ✓ Cancel anytime

Most popular

Data entry included


$79 /year

$6.60/month billed annually

  • yearly
  • 5 reports free
  • ✓ Instant interpretations
  • ✓ 4000+ biomarkers explained
  • ✓ Nutrition recommendations
  • ✓ We enter 5 reports for you
  • ✓ Yearly subscription
  • ✓ Cancel anytime

Data entry included


$250 /once

own it for life

  • pay once
  • 10 reports free
  • ✓ Instant interpretations
  • ✓ 4000+ biomarkers explained
  • ✓ Nutrition recommendations
  • ✓ We enter 10 reports for you
  • ✓ No subscription
  • ✓ Dedicated support
  • ✓ Unlimited access

Are You a Health Professional?

Get started with our professional plan

Welcome to Healthmatters Pro.

Save time on interpreting lab results with the largest database of biomarkers online. In-depth research on any test at your fingertips, all stored and tracked in one place. Learn more

Pro Monthly Plus

for health professionals

  • ✓ Track multiple clients results
  • ✓ No setup fees
  • ✓ No hidden costs
  • ✓ Instant interpretations
  • ✓ 4000+ biomarkers explained
  • ✓ Includes data entry service
  • ✓ Personal training and support
  • ✓ Cancel anytime

$75 per month

Use promo code to save 10% off any plan.

We implement proven measures to keep your data safe.

At HealthMatters, we're committed to maintaining the security and confidentiality of your personal information. We've put industry-leading security standards in place to help protect against the loss, misuse, or alteration of the information under our control. We use procedural, physical, and electronic security methods designed to prevent unauthorized people from getting access to this information. Our internal code of conduct adds additional privacy protection. All data is backed up multiple times a day and encrypted using SSL certificates. See our Privacy Policy for more details.