Coding, Billing, and Reimbursement Concepts
This domain connects documentation to code to payment. Expect items on code-set structure, modifiers, edit systems, and the payment methodologies that determine what a claim actually pays - plus the claim logic errors that produce denials or overpayments.
Code sets and structures
ICD-10-CM captures diagnoses with up to seven characters, laterality, and placeholders; ICD-10-PCS captures inpatient procedures. CPT and HCPCS Level II cover outpatient services, drugs, and supplies. Modifiers carry meaning: 25 (significant, separately identifiable E/M with a procedure), 26 (professional component only), TC (technical component), and the X{EPSU} modifiers that replaced 59 for distinct services. New and established office E/M levels are set by medical decision making or total time; prolonged-service add-ons require the threshold time to be documented.
How payment is calculated
- Physician: RBRVS = (work RVU × GPCI + practice expense RVU × GPCI + malpractice RVU × GPCI) × conversion factor. Geographic practice cost indices adjust for locality.
- Hospital outpatient: OPPS assigns services to APCs; status indicators determine separate payment, packaging, or no payment.
- Inpatient: MS-DRG assignment from principal diagnosis, secondary diagnoses, procedures, and CC/MCC status - with present-on-admission flags affecting which secondary diagnoses count.
- Surgical global package: preoperative, intraoperative, and postoperative care bundled for 0, 10, or 90 days; unrelated E/M during the global period needs a modifier and documentation.
Edit systems
NCCI procedure-to-procedure edits pair a payable Column 1 with a bundled Column 2 code; the modifier indicator shows whether a bypass is ever allowed. Medically Unlikely Edits cap units per day. Unbundling, upcoding, and duplicate claims are the classic errors these edits catch.
Worked example
A patient has a level-3 office visit and a same-day shave biopsy. The claim bills both without modifier 25. The reasoning: the E/M is payable separately only if it was significant and separately identifiable from the procedure - for example, evaluating a separate chronic condition. If the note documents only the lesion and the decision to biopsy, the E/M is bundled into the procedure and should be removed, not merely given a modifier.
Traps that cost marks
- Using modifier 59 as a universal bypass instead of a specific X modifier with documented distinct service.
- Assuming a code is payable because it exists in CPT.
- Ignoring the global surgical package when an E/M appears during follow-up.
- Mixing up professional and technical component billing.