Warning: If you fail to use your NPI by March 1, your Medicare claims won't pay. Providers have been gearing up for the May 23 deadline for submitting Medicare claims with only National Provider Identifiers in the primary fields. But an earlier March 1 requirement to use NPIs on Medicare claims, with or without an accompanying legacy number, may take providers by surprise and reduce their cash flow to a trickle. Once March 1 arrives, "you will not be able to get paid for any Medicare services you provide until you begin using your NPI," the Centers for Medicare & Medicaid Services stresses in a recent email message to providers. And the NPI has to match up with your old Medicare number. If it doesn't, none of your claims will pay. "If needed, you must correct any data which may be preventing an NPI/legacy match on the NPI crosswalk," CMS says. Time drain: "The correction might require that you file a CMS-855 Medicare Provider Enrollment form with your Medicare carrier, A/B MAC, or DME MAC " a process which can take a number of months to accomplish," CMS warns in the message. CMS is trying to "raise the level of urgency" about the March 1 deadline, it says. However, the agency already is receiving "well over 90 percent" of claims with an NPI in the primary fields, it acknowledges. If you're already using your NPI in the primary fields, it's time to set your sights on the next hurdle " NPI-only claims. "There is a very small percent of claims submitted with NPI- only," CMS reports. "The time for correcting problems, should there be any, is getting short." Do this: Test small batches of NPI-only claims to get a preview of how your claims will fare once the May 23 NPI-only deadline takes effect. Besides the obvious payment problems, NPI non-compliance could also bring administrative penalties, CMS threatens. Enforcement "penalties will be a legitimate resolution if the entity does not demonstrate compliance or corrective action," the agency says in another NPI email message. Resource: More information about NPIs is at http://www.cms.hhs.gov/NationalProvIdentStand.