For an
Update Letter Format, I suggest something like this:
Should not exceed one page. I would address it to the Admissions Committee. I feel a snail-mail letter is more formal, and thus preferred, but either will do the job. Don't do a simultaneous e-mail.
(If appropriate, start with expressing appreciation for the honor of your recent interview.)
Say you want them to be aware of updates pertinent to your application in case it may help them make a decision on your file:
a. You might give your fall/spring GPA depending on the time of year, perhaps mentioning some classes specifically relevant to med school.
b. Tell them any newly begun activities and any accomplishments (pubs)or ongoing-activity with additional hours since you submitted (only the important stuff).
You might close with why their school is perfect for you, trying to mesh with the school's mission statement. Say you look forward to hearing from them in the future regarding interview or acceptance as appropriate.
Then sign your name.