Trimethylamine, Urine

Diagnostic Use

Diagnosis of trimethylaminuria requires the measurement of TMA and TMAO in urine, which should be collected after an evening meal containing substrate.

Trimethylamine (TMA), formed in the intestine by bacterial action on various foods, is absorbed across the gut wall and oxidised in the liver to trimethylamine oxide (TMAO) by flavin-containing monooxygenase 3 (FMO3).

Excess TMA results in a characteristic “fishy” odour in sweat, breath and urine – trimethylaminuria (TMAU). This may be primary TMAU, caused by biallelic mutations in the FMO3 gene and subsequent loss of FMO3 function, or secondary TMAU, due to dietary overload, intestinal bacterial overgrowth or urinary tract infection5.

Sufferers can meet serious social difficulties, leading to isolation and depression. Symptoms can be improved by dietary restriction of seafood, lecithin-containing fish oil supplements, liver, kidney, legumes, eggs, peanuts, meat - foods high in TMAO or choline; of brassicas which contain indols (inhibitors of FMO3 enzyme activity). Antibiotics reduce bacterial production of TMA and use of pH 5.5 soaps help make it less volatile. In the case of mutations that do not completely abolish FMO3 activity, supplements of riboflavin might help maximize residual enzyme activity. Fermented foods or drinks may help reduce bacterial production. There are support groups for patients with body odour: email:


Specialist Biochemistry

Delphic Registration Code


Laboratory Handling


Early morning urine


Specialist Chemistry freezer



Turnaround Time

6 weeks