my 'grey area' I think would be higher at 90-95%. especially if they have a history of odor. I'm subjectively choosing this on reading papers. I would also test a few times rather than once to see if there is an average (unless the first test and perhaps 2nd are very low and obvious fails)
There seems to be 2 ways of choosing a ref range.
1 subjectively
2 an equation using the median average of 'normals' (-5% or something)
I think researchers usually go with a subjective range, having worked with synthetic fmo3 in a lab or whatever (don't know if that plays a part in their ref range). And testing labs that test people tend to go with the median equation. My impression is that researchers feel the enzyme should be near 100% to function completely whereas testers go very conservative. I reckon there are too many 'carriers' that a 'median normal' range will always be skewed too low.
Im not sure the Dutch lab uses 50%. I think i saw that on the net. I think they all used 50% to start with and have kept raising the threshold.
Yes metabolized and unmetabolized are the same thing in opposite wording. UK also uses a ratio which is the same again but you need to use an awkward equation to compare to the above.
I used the word nitrogen as the enzyme oxidizes many sulfides and amines (mainly) in a certain structure, with nitrogen meaning the 'amines'. But I think I read somewhere that the 'amine' function can be ok but the sulfide function can be faulty, so I don't feel confident enough to say TMA is an excellent biomarker of FMO3 function overall. Only for 'FMO3 amine (or nitrogen)' function
I think ultimately the correct therapy will be something like a 'low FMO substrate' diet or something similar to that (eg kill sulfide and amine bacteria) but at the moment TMAU is the only diagnosis on offer. There is also the added problem of biogenic amines (hormones etc). Some of these may be FMO3 substrates or inhibitors so it may be that they play some complicating role too.
It may be that a low FMO3 substrate diet is too difficult to follow.