We are currently experiencing logistical issues with this test and are busy looking for an alternative. In the meantime we have made this test unavailable but will fulfil any outstanding orders. Please check back here soon for updates.

What is TMAU?

Trimethylaminuria (TMAU), often referred to as “fish odour syndrome”, was first detected in 1970 by a group of doctors in Colorado who tested a child who was said at times to have a “fishy odour”.

Primary TMAU (also known as genetic TMAU) is caused by a defect of the FMO3 enzyme that should turn the (smelly) trimethylamine (TMA) into the odourless TMA-oxide.

Secondary  TMAU is not genetic. The main cause is an overgrowth of bacteria in the gut that produce TMA.

Symptoms are caused by a build up of the smelly TMA which is the excreted via the urine, sweat, breath and reproductive fluids leading to the characteristic fishy odour.

There are no physical symptoms associated with TMAU other than an unpleasant odour, but social and psychological symptoms are common due to the nature of the condition. Many people with TMAU seem to suffer intermittent or transient odour symptoms.

Where does TMA come from?

Primary TMAU

A genetic inability to convert TMA into TMAO will lead to a build up of TMA and the characteristic odour.

Secondary TMAU

Secondary TMAU is formed in the gut by the action of bacteria on certain foods that primarily contain choline and carnitine – for example, eggs, certain legumes, fish and organ-meats. It can also be naturally found in certain seafood as TMA-oxide, which is broken down in the gut to TMA.


Symptoms of TMAU

In small quantities, a build up of TMA can cause halitosis (bad breath) – a fishy or garbage-like odour – but a greater build up of TMA can cause a smell of rotting fish as well as being sulphurous.

Symptoms can be present from birth, but most people seem to develop symptoms around puberty and through the teens. TMAU can also develop much later in life.

In women, symptoms can be more severe just before and during menstruation, after taking oral contraceptives and around the time of menopause.

Useful links to help you find out further information about TMAU

Please note: Not all causes of malodour are ruled out by this test. Malodour can be caused by other volatiles such as hydrogen sulphide, methanethiol and dimethyl sulphide. Unfortunately we cannot test for these at this time.

Free Trimethylamine (TMA) /Creatinine ratio
TMA-N-Oxide Creatinine ratio
% N-Oxidation
Urine Creatinine



You can only currently collect the test kit and return the samples by hand to the laboratory in London. Test kits cannot be posted. The samples must be collected over a 24 hour period so collection of the kit and the return of the samples cannot be done on the same day.

Please stop all current supplements for a 3 to 4 days before completing the test.

Many people restrict their diets in an attempt to control and reduce odour, but this may affect the test results so we do not recommend you do this before testing.

For diagnostic clarity, we recommend that the sample is collected when odour is at its maximum. This may mean increasing dietary intake of choline (eg. pulses, eggs, liver) and carnitine (red meat) a few days before you take the test. Dietary ‘loading’ is possibly most effective with a simple high choline meal of 2 eggs and 400g baked beans the evening before completing the test. Your test will come with full instructions about this.

Please avoid cruciferous vegetables – cabbage, broccoli, cauliflower and Brussel sprouts before completing the test. Indoles in these vegetables naturally inhibit the FMO3 enzyme which would skew the result.

If you are worried about odour at certain times, such as around menstruation, it is important to collect urine at that time.


Adults and children.

Children must be able to supply a sample of urine that is free from nappy fibres and stool samples.


Samples must be returned by hand they cannot be posted.

6 weeks.

Your test results will be emailed to you.