The letter at the end of a Medicare number is used to indicate the type of beneficiary that a person is. For example, the letter A at the end of a Medicare number indicates the primary wage claimant, and this person is usually the primary earner; B indicates a spouse.
Each beneficiary on a Medicare plan has his or her own code and Medicare number. The Medicare number is typically the beneficiary's Social Security number plus the letter code. A beneficiary's Medicare number is used on all documentation from Medicare including letters, as well as any claims that are submitted by the member or medical personnel.