Trimethylaminuria 'carrier' test

For the Trimethylaminuria phenotype test (urine test), it is common for the lab to suggest 'provoking' the symptom, usually by taking a choline dose before testing. The lab is checking if following happens :

choline - altered by gut bacteria to TMA - absorbed and how much is converted to TMAO

There is also a variation of the test for people to test and see if they are genetic 'carriers' of TMAU. This is done by taking a trimethylamine dose before doing the same test.

 TMA- how much is converted to TMAO ?

It's not known how many labs suggest this test, but the only person to write papers on this variation of testing suggests a 600mg dose of TMA should be enough to detect carriers. At 900mg, most people are expected to fail to convert enough to be classed as normal. At 600mg, only carriers and sufferers are expected to fail. Only sufferers are expected to fail lesser doses.

This paper tells of the background of coming to this conclusion of setting the level for detecting genetic carriers of TMAU, and again interestingly notes that 1% of random people tested 'failed' the carrier test. It is also noted that "80%" seems to be the 'cut-off' level in this study, whereas today this is probably set at "85%". The paper was published in 1995

An oral trimethylamine challenge test has been used to confirm the heterozygous status of patients with 'fish-odour syndrome'. By measuring the percentage of total urinary trimethylamine-related material excreted as the N-oxide, no discrimination could be made between obligate heterozygotes (parents of 'fish-odour syndrome' patients) (n = 15; 96 +/- 2%, range 92-98%) and control individuals (parents of unaffected children) (n = 16; 96 +/- 2%, range 93-99%) on a normal diet. However, after ingesting a trimethylamine load (600 mg base) the obligate heterozygotes were clearly distinguishable (76 +/- 3%, range 71-79%) from controls (95 +/- 2%, range 91-99%) (t-test; p <0.001). One of a hundred apparently normal volunteers who were subsequently challenged with trimethylamine had a N-oxidation capacity which fell within the range found among the obligate heterozygotes.

http://www.ncbi.nlm.nih.gov/pubmed/8750603