March 7 (Reuters) - Medical device maker Dexcom DXCM.O said it has received a warning letter from the U.S. Food and Drug Administration following inspections of its two key manufacturing facilities, sending its shares down nearly 7% after the bell.

The warning letter identified issues in manufacturing processes and quality management system at Dexcom's facilities in San Diego, California and Mesa, Arizona.

The company did not provide details about how many observations were made at the two sites, but said it does not "expect a material impact" from the letter to its manufacturing capacity or its sales guidance for fiscal year 2025.

Dexcom said it had already submitted responses to the so-called "Form 483" and is in the process of preparing a written response.

A Form 483 is a type of agency report containing "observations" that FDA inspectors "deem to be objectionable."

Dexcom manufactures its products at its headquarters in San Diego, California and at its manufacturing facilities in Mesa, Arizona and Penang, Malaysia, according to a recent regulatory filing.

It collectively operates about 80,600 square feet of laboratory space and about 159,600 square feet of controlled environment rooms across the three facilities.

(Reporting by Arasu Kannagi Basil in Bengaluru; Editing by Arun Koyyur)

((ArasuKannagi.Basil@thomsonreuters.com;))