Truly is probably not going to be an issue. My blood results were abnormal as well (anemia, also, in fact), but the results were nothing that required medication or immediate intervention. Even with the abnormal values (which WERE on my medical papers), my permanent residency was granted in less than 2 weeks. Also, my BMI was like 28 or 29, not exactly a skinny-minny, but nothing that alarmed the application reviewers!
Also, as a former nurse in the US, I would question your MD about putting the "high risk for diabetes" in his report! The *fact* is that he does not have diabetes, whether he will or won't in the future is not the case unless he has *diagnosed* conditions that could exacerbate his chances of developing it, eg, obesity, insulin resistance or pre-diabetes (fluctuating blood sugar levels and consistently elevated hgba1c numbers). If your son has none of these, and only a familial history that predisposes him to a higher risk of developing diabetes, well, that's really not something that should be indicated in his medical report, as it is a SUPPOSITION based on history, not current or past medical history of the patient himself.
Just wanting to help. Lots of times US doctors struggle to know how to fill out forms properly and either don't put enough, or put too much and it makes things look way worse than they are. My tip as someone who has filled out literally thousands of forms for befuddled and frazzled MD's: tell him EXACTLY what you want on the form, and what you don't: I DON'T want my son marked as 'potentially' having a disease that he DOES not have, Doctor.
Ok, rant over. You might even be beyond this stage, and if so, sorry if it's old news! lol
Cheers!