** Shares of medical device maker Dexcom DXCM.O fall 3.9% to $74.82 premarket

** Late on Friday, DXCM said it had received a warning letter from the U.S. FDA following inspections of its two manufacturing facilities in San Diego, California and Mesa, Arizona

** Company said it has already submitted responses to the so-called "Form 483" and is currently preparing a written response

** A Form 483 is an agency report that includes "observations" made by FDA inspectors regarding practices or conditions they find "objectionable

** Stock has fallen 41.6% in the past 12 months

(Reporting by Padmanabhan Ananthan)

((Padmanabhan.Ananthan@thomsonreuters.com))