Medicare Primary, FEHB Secondary

Talked with a guy (diabetic type 1 with CGM) who said Medicare was primary, FEHB secondary. When insulin is submitted to Medicare under Part B they deny the claim. But his FEHB pays anything denied by Medicare.

I don't think I have run into anyone (yet) who has Medicare and FEHB but found it odd the FEHB pays claims denied by Medicare. He is quite adamant in his statement but if this is true, why even bother with Medicare B? Why not pass Go and collect $200?

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