ACA CCS common mistakes
ACA CCS · Understand the traps and how to avoid them.
Assigning the ICD-10-CM code for a symptom (e.g., cough, abdominal pain) when the record documents a definitive diagnosis, or coding the presenting sign when a related definitive diagnosis is established.
Candidates learn symptom codes early and default to them, and they miss the ICD-10-CM Official Guidelines rule (Section I.B.4/IV) that signs and symptoms integral to a diagnosed condition are not coded separately.
What to do instead
Before finalizing a diagnosis code, scan the assessment/impression for a definitive condition; if one exists, code it and drop the symptom code unless the guideline or provider explicitly directs otherwise.
Coding from the operative report summary or the CPT index entry rather than reading the full operative body and verifying the root operation, body part, approach, and device for each PCS character.
Index entries point to a code family, not a final code, and summaries omit approach, device, or qualifier detail; candidates stop at the index instead of building the seven characters from the tables.
What to do instead
Read the entire operative note, write out the seven PCS character definitions (root operation, body system, body part, approach, device, qualifier) on scratch paper, then look up each in the PCS tables and confirm the code's full definition matches the documented procedure.
Selecting an E/M level based on the number of diagnoses listed or the length of the note rather than applying the documented medical decision-making or time rules.
Candidates equate longer notes or more diagnoses with higher complexity, and they apply older key-component habits instead of the current MDM (problems, data, risk) or total-time framework.
What to do instead
For each E/M encounter, tabulate the three MDM elements and choose the two-of-three level, or document total time on the date of the encounter; ignore note length and diagnosis count.
Reporting a bundled service separately (e.g., a procedure with a global period, or a component included in a surgical package) without checking NCCI edits or modifier justification.
Candidates see a distinct line item in the note or charge sheet and code it, unaware that the payment policy bundles it or that a modifier requires documented distinct circumstances.
What to do instead
Before adding a second code, check NCCI PTP edits and the surgical package rules; only append modifier 25, 59, or X{EPSU} when the documentation supports a separate, distinct service and the payer policy allows it.
Coding a diagnosis or procedure without confirming the documentation supports it (e.g., coding a condition 'ruled out' or 'probable' as confirmed in an outpatient setting, or coding a procedure not described in the body).
Candidates code what they expect or what the index suggests rather than what the provider documented; they also misapply inpatient vs. outpatient uncertain-diagnosis rules.
What to do instead
Apply the outpatient rule: code only confirmed conditions; for uncertain diagnoses use the guideline-appropriate code or query the provider. Verify every procedure code against an explicit operative description, and use a physician query when documentation is ambiguous.
Confusing laterality, sequencing, or specificity requirements-omitting the 7th character for injury codes, choosing the wrong episode of care, or sequencing the principal diagnosis incorrectly.
Candidates memorize code stems but overlook required characters and sequencing conventions, and they do not distinguish initial encounter, subsequent encounter, and sequela.
What to do instead
For every injury/musculoskeletal code, confirm the 7th character and episode; for every inpatient record, determine the principal diagnosis per the Uniform Hospital Discharge Data Set definition (condition chiefly responsible for admission after study). Verify all characters are present before submitting.
Mixing up code-set conventions-using CPT/HCPCS for inpatient facility procedures, or using ICD-10-PCS for outpatient/professional claims.
Candidates learn all code sets but lose track of which setting uses which system, especially on integrated or transition-of-care scenarios.
What to do instead
Anchor the setting first: inpatient facility = ICD-10-PCS for procedures and ICD-10-CM for diagnoses; outpatient/professional = CPT/HCPCS for procedures and ICD-10-CM for diagnoses. State the setting aloud before selecting any procedure code.
Ignoring payer-specific and regulatory rules-missing medical necessity (LCD/NCD), modifier requirements, or timely filing and clean-claim edits-when assigning codes and completing the claim.
Candidates focus on code accuracy and treat reimbursement as an afterthought, forgetting that a correct code can still be denied for lack of medical necessity or a missing modifier.
What to do instead
Before claim submission, run a checklist: diagnosis supports the procedure per LCD/NCD, required modifiers present, place of service correct, and claim scrubbed for edits. Treat medical necessity as part of coding, not a separate billing step.
Assuming a term means what it sounds like-coding 'history of' as an active condition, confusing 'status' with 'history,' or picking a code from a similar-sounding term without checking the alphabetic index and tabular list.
Medical terminology and pathophysiology knowledge gaps lead candidates to code by superficial resemblance rather than verified meaning; they skip the cross-reference in the index.
What to do instead
For every unfamiliar or ambiguous term, look it up in the alphabetic index including cross-references, then confirm in the tabular list; distinguish 'history of' (Z codes), 'status' (Z codes), and active conditions. Build a personal glossary of look-alike terms.
Submitting or releasing coded data without an internal quality check-no reconciliation of codes against the record, no audit of high-risk codes, and no review of data-quality flags.
Candidates treat coding as a one-pass task and skip the verification step, and they are unfamiliar with data-quality dimensions (completeness, accuracy, timeliness, consistency).
What to do instead
Perform a structured self-audit on a sample of records: re-read the documentation against each code, verify principal diagnosis and DRG impact, and document any query or correction. Track error patterns and apply data-quality checks before the record is finalized.