Question: Can you help me understand what criteria are used by Medicare in their claims review process to assess “medical reasonableness”? California Subscriber Answer: Having clarity about how CMS assesses whether a procedure or service is medically necessary can help you file accurate claims. According to CMS, “medically necessary” is defined as “Health care services or supplies needed to prevent, diagnose or treat an illness, injury, condition, disease or its symptoms and that meet accepted standards of medicine.” Where to look: To verify medical reasonableness or medical necessity of a diagnosis and associated procedure/s under CMS, you should review the Local Coverage Determinations (LCDs) or National Coverage Determinations (NCDs) for your Medicare carrier.