Coding: Diagnosis and Procedure
The code sets
ICD-10-CM carries diagnoses; CPT describes professional services and procedures; HCPCS Level II covers drugs, supplies, and G codes. ICD-10-CM conventions matter: start in the Alphabetic Index, then verify in the Tabular List. Watch for laterality, 7th characters for encounters and obstetrics, "code also" instructions, Excludes1 (never reported together) versus Excludes2 (not included but reportable separately when documented), and sequencing rules that place the condition chiefly responsible for the encounter first.
CPT and modifiers
The E/M level must be supported by the documented history, examination, and medical decision making, or by time when the code set allows it. Key modifiers: 25 for a significant, separately identifiable E/M on the same day as a procedure; 26 professional component and TC technical component; 59 or the X{EPSU} family to identify a distinct service that overrides an NCCI bundling edit; 50 bilateral; LT/RT laterality; 51 multiple procedures; 22 increased procedural services. Never apply a modifier to defeat a payer edit without documentation that supports the distinct service; doing so is unbundling and a compliance risk.
Medical necessity
A diagnosis must justify the service. NCCI edits are coding rules, not clinical judgment, and they apply regardless of payer.
Traps
Coding from the superbill rather than the note. Reporting a sign or symptom when a definitive diagnosis is documented. Dropping a laterality or 7th character. Using an unlisted code with no comparison code and no supporting note. Choosing an E/M level the documentation does not support (upcoding).
Rule of thumb
Code what the provider documented and medically decided. If the record is ambiguous, query the provider rather than guessing, and never assign a code only to make a claim pay.