I have been going meticulously through the First Aid for the USMLE while looking up everything I couldn't remember on the side. I have encountered quite a few instances where the information in the First Aid is not the same as the information listed elsewhere.

For instance:

First Aid says, that HLA-DR3 is associated with Goodpasture, MS, Hay fever and SLE.
On wikipedia it says: DR2 serotypes are associated with Goodpasture syndrome, multiple sclerosis,[2] and narcolepsy, tuberculoid leprosy[3] (multi-drug resistant tuberculosis or leprosy),[4] ulcerative colitis(Japanese),[5] primary biliary cirrhosis and autoimmune hepatitis.[6] DR2 is also found in all patients that test positive for anti-anti-Asn-RNA-synthetaes and chronic interstitial lung disease.[7]

It doesn't bother me, that some diseases are left out, but the hay fever and the SLE is not mentioned at all.
This is just one example out MANY (And yes I do think that wikipedia is usually right when it comes do articles on medicine). I have only gone through the immunology so far, which admittedly is probably one of the fastest changing topics.

What do you guys think? Is the First Aid trustworthy?

Wikipedia is free for all not a good or reliable source because anyone can edit it and put whatever information they like there. try another source.