Noridian's Local Coverage Determination (LCD L38803) clearly distinguishes diagnostic from therapeutic facet joint injections, outlining specific requirements for each to ensure appropriate use and coverage.

Diagnostic facet joint injections, performed as medial branch blocks (MBB) or intra‑articular (IA) injections when MBB cannot be done, are used to determine whether the facet joints are the true source of chronic axial neck or low back pain. To qualify, a beneficiary must meet LCD criteria, including pain lasting at least three months, failure of conservative therapy, and no alternative diagnoses. Diagnostic injections must be intended to guide treatment toward radiofrequency ablation (RFA) if positive. A second diagnostic block is allowed only when the first produces at least 80% pain relief, and Medicare limits diagnostic sessions to no more than four per spinal region in a 12‑month period.

The KX modifier should be appended to the line for all diagnostic injections. In most cases the KX modifier will only be used for the two initial diagnostic injections. If the initial diagnostic injections do not produce a positive response as defined by the policy and are not indicative of identification of the pain generator, and it is necessary to perform additional diagnostic injections at a different level, append the KX modifier to the line.

Therapeutic facet joint injections, by contrast, are intended for pain management when RFA is not appropriate. To qualify, the beneficiary must first have two diagnostic blocks, each confirming ≥80% pain relief. Ongoing therapeutic injections must then demonstrate at least 50% pain relief lasting three months or comparable improvement in function. Medicare also limits therapeutic sessions to four per spinal region in a rolling 12 months, and documentation must clearly explain why RFA cannot be performed.

In summary, diagnostic injections identify the pain generator, while therapeutic injections treat confirmed facet‑mediated pain when RFA is not an option. Both require consistent pain and functional measurement tools and strict adherence to LCD criteria for coverage.