You've washed, changed your clothes and switched soap, and the smell is still there. Then one night you read about trimethylaminuria, and for the first time something seems to fit. Friends or doctors may have put it down to hygiene, diet or stress, and you know that isn't the whole story.
That frustration is real, and so is the smell. But a familiar smell is a clue, not an answer. TMAU, also called fish odour syndrome, is uncommon, and a few ordinary, treatable conditions cause the same complaint. Check those first, and if the smell is still there, a specialised laboratory test gives you a firm yes or no.
Already had the common causes checked and want that answer now? Blood London offers a TMAU test by enquiry, with no GP referral needed. It costs £506.25 and results take about 6 weeks. It is a urine test, so there is no blood draw fee. To arrange it, contact the clinic on 020 7183 0244 or use the enquiry form on the test page.
Why smell alone can't settle it
Smell is personal, it comes and goes, and it's hard to describe in a ten-minute appointment. You may notice it when nobody else does, or the other way round. Hormones, heat, exercise, stress and yesterday's clothes all change it, whether or not you have a metabolic condition.
Metabolic Support UK, which provides the NHS-facing information on this condition, is explicit that a TMAU diagnosis needs a specialised laboratory measurement. Until then, you have a symptom with a shortlist of causes. Guessing wrong can mean months on a restricted diet and a delay in treating something ordinary and fixable.
What TMAU actually is
In the inherited form, the FMO3 gene makes too little of an enzyme the body needs. That enzyme normally turns trimethylamine, a compound made in the gut from certain foods, into something odourless. Without enough of it, trimethylamine leaves the body in sweat, breath and urine.
People describe fish, eggs, rubbish or urine. Women sometimes notice it more around periods, and it can flare at puberty, so scientists think oestrogen and progesterone may make symptoms more obvious. It also varies from day to day.
Apart from the smell, most people with TMAU are otherwise well, and it does not shorten life. It is rare: public information still cites around a hundred identified cases. Milder symptoms are easy to miss, so it is probably under-diagnosed, and people who have it often wait a long time to be believed.
The inherited form is autosomal recessive. Both parents carry one working FMO3 gene and one faulty one, and each child has a one-in-four chance of inheriting two faulty copies. Relatives can look at testing once one person in the family has a confirmed result.
What else smells like this
A urine infection can make urine and clothing smell sharp or fishy, often with burning or needing to go more often. It's common and treatable. If you have burning, a fever or a sudden change in urine smell, see a GP that week to have an infection checked.
Bacterial vaginosis is a frequent cause of a fishy vaginal smell, especially after sex. It's common, it says nothing about how you look after yourself, and a sexual health assessment is the quickest route to an answer and treatment.
Gum disease, dental infection and tonsil stones can put a rotten or fishy smell on the breath, and a dentist or GP can often see the cause. Ordinary sweat, trapped moisture and clothes worn through a commute do the rest, particularly in warm weather.
Diet can change body odour too. Hold off any severe low-choline plan until you've been tested, because changing your diet early can cause adverse nutritional effects for the wrong reason.
What a good GP appointment looks like
A good first appointment is unglamorous. It checks for infection, reviews your medicines, asks about vaginal or urinary symptoms, and may send you to a dentist. It should also take the social cost seriously: persistent unexplained odour is strongly associated with embarrassment, withdrawal, anxiety and depression.
Starting with the common causes is good medicine, because that's where the numbers are. What matters is that someone comes back to the question if the smell is still there once those have been treated.
NHS metabolic services exist, but they usually need a specialist referral, and TMAU is uncommon enough that many GPs will never have ordered the investigation. If you'd like to talk the symptoms through with a doctor first, book a private GP consultation at Medical Express Clinic.
When to book a TMAU test
Book a test when the common causes have been looked at, the smell is persistent, and you want a clear answer rather than another year of deodorant advice. It's also the right step if a specialist has asked for it or a close relative has confirmed TMAU. And it gives you a formal report without waiting to be believed.
What the test involves
Diagnosis needs a specialised measurement of trimethylamine, usually on urine. Some people are asked to collect more than one sample, and some also have genetic testing of FMO3 to confirm the inherited form. The laboratory answers one narrow question: is trimethylamine building up, or is the smell coming from something else?
The clinic arranges the test at a UKAS-accredited laboratory, so the result comes back as a formal report a doctor can work with and interpret. Any preparation, including dietary instructions, comes from the laboratory, and you'll be told when the appointment is made.
If the result is negative
A negative result is useful. It means the smell has a different explanation. You can go back to the common list with more confidence: urine, vaginal infection, dental disease, sweat and clothing, and medicines. Blood London doctors can review the report with you and help you decide what to do next, or you can take it to your NHS GP.
It is possible to feel both relieved and furious. Relief that it isn't TMAU, and fury that you were left to get there yourself. Both can be true.
If the result is positive
TMAU has no cure, but it can be managed. That often means dietetic advice, simple changes to washing and clothing, and support for the anxiety or isolation the smell can cause. With the diagnosis confirmed, a clinician or dietitian can tell you which changes are worth making.
You can take the report to your NHS GP, or book a consultation with a Blood London doctor to go through it. After that consultation, the doctor can refer you onwards for private treatment if you want it. Family members who want to know their own carrier or affected status can then be pointed to genetic testing.
Frequently asked questions
Can I tell if I have TMAU from the smell?
The smell is what brings you here, and the answer comes from the laboratory: a measurement of trimethylamine, sometimes with genetic testing as well.
How common is TMAU?
It's rare. Published patient information still refers to around a hundred identified cases and notes that milder forms are probably missed, so the common causes are still the place to start.
If it isn't TMAU, what is it likely to be?
Often a urine infection, bacterial vaginosis, gum or dental disease, or ordinary sweat and clothing. Each of those is treatable.
Should I change my diet first?
Wait for a result, unless a clinician has given you instructions for a specific test. Changing your diet early can cause adverse nutritional effects for the wrong reason.
Do I need a GP referral?
No. The test is arranged by enquiry: call 020 7183 0244 or use the enquiry form on the test page. You can still take the report to your NHS GP afterwards.