HCPCS "S" Codes: What are they?

I recently completed a consulting project for a client that required researching commercial payer coverage policies for a specific procedure. What I found was that, in addition to a list of relevant CPT codes for the particular service I was researching, there was a host of HCPCS “S” codes that were included in some of the coverage policies. It occurred to me that these are not codes you come across every day, so I took the opportunity to refresh my understanding of these codes. I’ll share with you what I learned.