FWA Insights: How SIUs can identify misuse of the unlisted home visit code

Unlisted procedure codes play an important role in healthcare billing, allowing providers to report services that do not have a more specific CPT or HCPCS code. But because these codes are inherently less defined, they can also create vulnerabilities when used too broadly, too frequently, or without clear documentation. CPT 99600, an unlisted code used to bill for home visit services or procedures, is one such code that may warrant closer review when billing patterns appear atypical.

In this edition of FWA Insights, we explore how special investigative units (SIUs) can identify potential misuse of CPT 99600 by combining claims data analysis, peer benchmarking, and documentation review to better understand whether billing behavior reflects legitimate care delivery or possible fraud, waste, and abuse (FWA).

Investigative steps  

In one recent review, Cotiviti’s SIU investigators identified a provider with excessive reliance on CPT 99600. Claims data covering a 12-month billing history showed that CPT 99600 accounted for 100% of the provider’s total billed revenue, where 100% of the provider’s Medicare and Medicaid patients were also listed as recipients of unlisted home visits. Use of CPT 99600 generally occurs only when no specific, valid CPT or HCPCS code accurately describes the service performed. Due to the highly atypical utilization of this unlisted code, further review was warranted.

The provider also repeatedly billed 99600 alongside a consistent cluster of CPT Category II quality-reporting codes (3044F, 3051F, 3074F-3080F, 1123F-1170F, and 4010F), which are typically not reimbursed separately. While repeated code combinations do not automatically indicate improper billing, highly repetitive patterns may suggest template-driven billing or services that require additional documentation to confirm that the care provided supports the claims submitted.

To assess whether the billing behavior was consistent with peers, Cotiviti investigators drew from peer comparisons and identified the provider as an outlier. This outlier status became more actionable when combined with other indicators, including full-revenue dependence on an unlisted code, universal use across all patients, and repeated code pairings that appeared inconsistent with typical billing variations. The investigation is ongoing and continues to be monitored by the team.  

Determining the validity of claims 

Health plan SIUs reviewing similar activity should begin with data analysis to identify providers with extreme utilization of CPT 99600 or other unlisted codes. From there, consider these steps to determine the validity of claims: 

• Compare utilization against relevant peer groups  

• Review claim histories for repeated code combinations 

• Request supporting documentation to determine whether the billed services were appropriately described, medically necessary, or not reportable under a more specific code 

Key takeaways   

Procedure code 99600 should be reserved for home-based services that are not otherwise captured by an existing CPT or HCPCS code. When a provider relies heavily or exclusively on an unlisted code, SIUs should prioritize review to determine whether the billing is supported by clear documentation and aligned with coding requirements.

Outlier analysis is most effective when viewed alongside other warning signs, such as repeated code combinations, abnormal claim patterns, or unusual claim lifecycle behavior. By combining peer benchmarking with documentation review, health plans can better identify potential misuse of unlisted codes and reduce improper payments to preserve appropriate reimbursement for legitimate services.

Sustainable payment integrity requires more than just the latest technology. Effective programs depend on intentional prevention strategies supported by governance, accountability, and collaboration between health plans and partners.