Medicare retroactive to transplant- bill as secondary?

[Guest guest]

When a patient with a EGHP signs up for Medicare after transplant and it is made

retroactive to the month of transplant, should Medicare be billed as a secondary

payer?

Example: Patient received transplant on April 14, 2011 and our hospital only

billed the EGHP. (Payment received in May and adjustment made to account.)

Patient enrolled in Medicare in August, and Medicare effective date is April 1,

2011. Do I need to advise the hospital billing dept to bill Medicare as a

secondary payer?

Thanks!