CO-50: Not deemed a medical necessity

What it means

CO-50 means the payer's medical necessity criteria were not met for the service as submitted. The determination is usually based on the diagnosis, documentation, or level of care compared against the payer's coverage policy or medical necessity guidelines.

Mechanically this can fire from an automated policy edit tied to diagnosis and code combinations, or from a clinical review of submitted records. Because it is a CO code the balance is contractual, but medical necessity denials are frequently appealable with stronger documentation.

Why it happens in behavioral health

Medical necessity is one of the biggest denial drivers in behavioral health. Payers apply level-of-care criteria such as ASAM for SUD or their own behavioral health guidelines, and a denial often means they believe the client did not meet criteria for residential, PHP, or IOP intensity on the dates billed.

Concurrent review denials also surface as medical necessity when a payer decides continued stay is no longer justified. The strongest defense is contemporaneous clinical documentation that maps directly to the payer's criteria, including risk, function, withdrawal, and treatment response, submitted with a focused appeal.

How to fix it

• Pull the payer's medical necessity or level-of-care policy for the denied service.
• Compare the clinical documentation against each criterion the policy requires.
• File an appeal with records that map symptoms, risk, and level of care to the policy.
• Request a peer-to-peer review when a clinical reviewer denied continued stay.

How to prevent it

• Document level-of-care criteria explicitly in the clinical record at admission and each review.
• Verify medical necessity and authorization align before delivering the level of care.
• Train clinical staff to chart to the payer's ASAM or behavioral health criteria.

Related denial codes