Question: We are getting a lot of denials for testing services with code N433. We are wondering what we are doing wrong to get this denial code.

Answer: Denial reason N433 Resubmit this claim using only your National Provider Identifier (NPI)
From the Fundamentals of Ophthalmic Coding 
The ordering physician’s national physician identifier (NPI) must be listed in box 17 when any tests are billed. Although there is space to identify up to three physicians, most report the ordering physician:

• DN — referring
• DK — ordering
• DQ — supervising physician

If more than one physician of the practice orders tests on the same day, it will be necessary to report them on separate claim forms.

Offices should promptly correct claims and refile the rejected line items only. This can be retransmitted electronically. If possible, corrections can also be made with the payer by phone.
Note: When the claim is rejected, it is as if it had never been received. There is no need to identify the claim as a refiled or corrected claim.