On your explanation of benefits or remittance, CO-55 means: procedure/treatment deemed experimental/investigational.
How often this type of denial gets overturned
Where state external-review programs publish outcomes for this denial category, the overturn rates are (reported separately — different programs, different denominators):
Program
Overturn rate
Cases
California DMHC IMR
45.3%
10,476
New York DFS
43.6%
2,211
Roughly half of externally reviewed denials in this category are overturned. A denial is a first decision, not a final one.
What to do next
This code is generally appealable. Internal appeal deadlines are typically 180 days from the denial.
If your denial arrived near-instantly or names no reviewing physician, several states now bar algorithm-only medical-necessity denials — ask in writing who reviewed the claim.
Always request an itemized bill and keep everything in writing.
Now turn the number into a dispute. Knowing your percentile is step one; the letter that cites it, the visit-code check, and the deadlines are the rest. Medigami builds those from your actual bill — medigami.com