I just searched for:
c3 c4 Lyme
and got some good leads to information.
My Lyme doc tested for C4, as I recall, but he didn't put a lot of weight on it. Also, it's a number that I seem to recall fluctuated a good bit, and also has a pretty wide range of 'normal' results, like 60-360, iirc.
Here's a quote from one of those websites, posted by a reader there:
"My daughter has elevated C4a but the doctor says the C3 reading does not give him adequate information because the reading is not precise, so he doesn't know if it is on the low side or the high side.
"He is suspecting Lyme, however, she was never bitten by a tick and where we live in Canada there isn't much Lyme. He said it can be transmitted via mosquitoes."
So the first paragraph above is what I have read generally, that the numbers are kind of squishy, but may be useful when read in conjunction with other measures. The 2d paragraph, tho, makes me almost laugh, if it weren't so serious: the parent says the kid 'was never bitten by a tick' -- that's sadly silly, because many many of us never saw a tick on us, partly because they are so tiny, or bite inside the hairline where they are never seen. Another sad point is the statement that 'we don't have much Lyme in Canada' -- sadly, Lyme is massively underdiagnosed and is pretty much everywhere. And finally, the doc apparently said mosquitoes can carry Lyme, which I have not read elsewhere, but I would be open to the idea until it's proven otherwise.
There is more about mold toxins etc on that website, which is at:
www.prohealth. com / me-cfs / blog /boardDetail . cfm?id=1329615
but don't get overwhelmed by it all. it seems to focus on chronic fatigue, which I personally suspect is just Lyme by another name, but then I'm not a doc.
In your situation, I'd spend some time on the 'right diagnosis' website noted above, maybe skim the 'prohealth' site just noted, and keep an open mind and be prepared to switch docs (or tag team the docs, seeing more than one at a time, without necessarily telling them about each other) if that seems sensible. Unlike other ailments, these mysterious ones require much from the patients in the way of strategizing, since the docs are sometimes clueless and sometimes have closed minds.
The good news is: you have options, and you're thinking critically and strategically. Let us know how it goes -- best to you and yours --