As of January 1, 2011 the Patient Protection and Affordable Care Act (PPACA) of 2010 requires all health insurance plans to begin covering preventative services and immunizations without any cost sharing requirements.
A cost sharing requirement means co-pays, coinsurance, or deductibles. If the preventative services are part of an office visit then the office visit may not have cost sharing if the primary reason for the visit is the preventative service. If the office visit and preventative service are billed separately and the primary reason for the office visit was not the preventative service then cost sharing is permitted for the office visit.
To better facilitate proper claim processing for preventative services, CPT modifier 33 has been created. This new modifier is effective January 1, 2011 and should be used when the primary purpose of the service is the delivery of an evidence-based service in accordance with a US Preventative Services Task Force A or B rating or other services identified in preventative services mandates (legislative or regulatory).
So to summarize from above:
Cost Sharing: Co-pay, Co-insurance, or Deductible (patient's portion to pay the provider of service)
Primary Preventive Services provided in-office WITHOUT an additional E&M type visit = NO co-pay, NO co-insurance, No deductible. These $ requirements should not be taken from the patient, nor should the 3rd party payer adjudicate for one.
Primary E&M visit with a Preventive visit on the same day: collect a co-pay or a deductible only applicable to the E&M service, and not to the preventive service. These co-pays may be adjudicated on your claim and on the EOB to the patient.
What this means to coders:
Modifier 33 informs carriers, that you believe that the preventive/screening service that you provided to your patient should not be subject to cost sharing, co-pay, co-insurance, or deductible.
Below is a good website to check out, it goes into detail regarding Modifier 33. This info is straight from the AMA regarding the implementation of modifier 33. This is a PDF document, so you can download. : )