ABA therapy billing is units-based and authorization-heavy, which means the same billing gaps that trip up physical therapy practices appear here too, layered with modifier rules specific to the ABA code set. Most ABA denials trace to one of four predictable patterns and are fully recoverable once you identify which one applies.
The ABA CPT code set
The eight ABA-specific CPT codes (97151 to 97158) replaced the older H-codes starting in 2019. Each codes to 15-minute increments, so a single session generates multiple lines. Payer authorizations typically control the total units approved per code per authorization period, which makes accurate unit tracking essential before claims go out.
- 97151: Behavior identification assessment. Must be performed by or under direct supervision of a BCBA. The baseline report this generates is critical documentation for medical necessity appeals on all other codes.
- 97152: Behavior identification supporting assessment. May be performed by a technician under BCBA supervision, co-billed with 97151 when additional time is required.
- 97153: Adaptive behavior treatment by protocol, per 15 minutes. One-on-one technician-delivered treatment. The highest-volume code for most ABA practices and the one most frequently targeted by authorization unit limits.
- 97155: Adaptive behavior treatment with protocol modification, per 15 minutes. Requires direct BCBA involvement. The code where missing or mismatched modifiers produce the most revenue loss per claim.
- 97156/97157: Family adaptive behavior treatment guidance, individual and multi-family group variants. Often short-paid when session time documentation is vague or lacks attendee names.
Pattern 1: Missing or mismatched modifier (CO-4)
Most commercial payers require the HO modifier on 97155 to confirm that a master's-level clinician delivered or directly supervised the protocol modification. Without HO, the payer either denies the line as a CO-4 (modifier inconsistent or missing) or pays it at the lower technician rate, which amounts to the same revenue loss with no denial flag. Some payers also require HA (child/adolescent program) or TJ (program for child with developmental delay), so maintain a per-payer modifier reference for your most common carriers rather than applying one modifier set to all claims.
Pattern 2: Authorization gaps (CO-15 and CO-197)
ABA authorizations typically control units per code, not just total hours. A common authorization structure approves 640 units of 97153 and 80 units of 97155 for a six-month block. The two failure modes are:
- Billing 97155 under an authorization approved only for 97153, which produces a CO-15 (authorization not on file or not applicable) denial on every 97155 line. The fix is separate authorization requests for each code at the initial approval.
- Exhausting the authorized unit count before the authorization period ends. The payer pays up to the approved units and denies the overage as CO-197. A concurrent-review request before units run out is the only clean solution; retroactive authorization is uncertain and payer-dependent.
Weekly tracking of units billed versus units authorized catches both problems early. Setting an internal alert at 80% of the approved block gives enough lead time to submit a renewal request before the session schedule is affected.
Pattern 3: Same-session bundling (CO-97)
When 97153 and 97155 both appear on the same date of service, payers commonly bundle them under CO-97, treating the protocol modification as part of the technician-delivered treatment rather than a separately identifiable BCBA service. The documentation requirement is specific: the session notes for each code must show non-overlapping start and end times. A 97155 block running from 10:00 to 10:30 and a 97153 block running from 10:30 to 12:00 are distinct services. The same start time on both is what draws the bundling. CO-97 appeals on 97155 succeed when the appeal packet includes those timestamps alongside a brief explanation of what the BCBA did during the protocol-modification period.
Pattern 4: Medical necessity challenges (CO-50)
CO-50 denials on ABA claims most often challenge the prescribed treatment intensity: the payer approves 10 hours per week and the practice bills 25. Appeals require the full behavior intervention plan, baseline data from the initial 97151 assessment, current reassessment data showing progress or lack thereof, and a BCBA narrative connecting the data to the specific intensity level. Payers look for evidence that the prescribed hours correspond to behavioral targets with documented necessity for that frequency. A letter restating the autism diagnosis without addressing hours does not meet that bar.
Texas coverage requirements
Texas Insurance Code Chapter 1355 requires state-regulated commercial health plans to cover ABA therapy for enrollees diagnosed with autism spectrum disorder, without the annual dollar caps that existed before the ACA. The mandate applies to plans subject to Texas insurance regulation. ERISA self-funded employer plans are not subject to it. Before escalating a denial to a Texas Department of Insurance complaint, confirm the plan is fully insured. Texas Medicaid covers ABA through the STAR and STAR Kids programs, with authorization administered by the managed care organizations; HHSC, not TDI, is the escalation path for Medicaid MCO disputes.
Working the backlog
ABA denial patterns repeat cleanly across claims: the same payer denies the same code for the same reason month after month. Sort your denied ABA claims by payer and CARC before working them one by one. A CO-4 modifier gap on 97155 across three months of claims is one billing-rule correction and one batch of corrected claims. An authorization unit overage is a process change to the concurrent-review trigger. The same root cause that drove 40 denials last quarter will drive 40 more next quarter without an upstream fix. See the denial management guide for how to structure the triage workflow and the revenue-leakage guide for sizing the recoverable backlog before committing staff time to it.