All in a day's work: counting days for Medicare reimbursement purposes.

CMS rules regarding what constitutes a patient day are often confusing and inconsistent. It is important for hospitals and their advisers to have a clear understanding of CMS's rules regarding what constitutes a patient day, the impact of those rules on Medicare payment, and instances in which CMS's rules may be subject to challenge. Lack of familiarity with the finer points of these rules may result in substantial underpayments for services rendered.