Clinical Classification Systems · 6 min read
Apply Outpatient Coding Guidelines · Apply Physician Coding Guidelines
Outpatient coding covers hospital outpatient departments, emergency departments, ambulatory surgery, observation, clinics, and physician offices. Section IV of the ICD-10-CM Official Guidelines governs diagnosis coding, and procedures are reported with CPT and HCPCS Level II rather than ICD-10-PCS.
| Topic | Inpatient (Sections II–III) | Outpatient (Section IV) |
|---|---|---|
| First code | Principal diagnosis: established after study | First-listed diagnosis: chiefly responsible for the encounter |
| Uncertain diagnoses | Coded as if established | Not coded; code signs, symptoms, or abnormal findings to the highest degree of certainty |
| Procedure code set | ICD-10-PCS | CPT and HCPCS Level II |
| POA indicator | Required | Not used |
| Chronic diseases | Report when they meet UHDDS 'other diagnosis' criteria | Report as many times as treated; code all documented conditions that coexist and affect care |
Encounter-Specific Rules
Physician (professional) coding reports services by physicians and other qualified health care professionals on the CMS-1500 or 837P. Diagnoses use ICD-10-CM (outpatient rules apply to physician services in every setting), and services use CPT and HCPCS Level II.
CPT Code Categories and Sections
| Section | Code range |
|---|---|
| Evaluation and Management | 99202–99499 |
| Anesthesia | 00100–01999, 99100–99140 |
| Surgery | 10004–69990 |
| Radiology | 70010–79999 |
| Pathology and Laboratory | 80047–89398 and 0001U–series |
| Medicine | 90281–99199, 99500–99607 |
Evaluation and Management (E/M) Level Selection
Office and other outpatient visits, hospital inpatient and observation care, consultations, emergency department visits, nursing facility services, and home or residence services are selected by medical decision making (MDM) or total time on the date of the encounter. Emergency department codes are selected by MDM only. History and examination are performed as medically appropriate but no longer determine the level.
| MDM level | Problems addressed | Data reviewed and analyzed | Risk of patient management |
|---|---|---|---|
| Straightforward | 1 self-limited or minor problem | Minimal or none | Minimal |
| Low | 2+ minor problems; 1 stable chronic illness; 1 acute uncomplicated illness or injury | Limited | Low (e.g., OTC drugs) |
| Moderate | 1+ chronic illness with exacerbation; 2+ stable chronic illnesses; 1 undiagnosed new problem with uncertain prognosis | Moderate | Moderate (e.g., prescription drug management) |
| High | 1+ chronic illness with severe exacerbation; acute or chronic illness posing a threat to life or bodily function | Extensive | High (e.g., decision regarding hospitalization) |
| MDM | New patient | Established patient |
|---|---|---|
| Straightforward | 99202 | 99212 |
| Low | 99203 | 99213 |
| Moderate | 99204 | 99214 |
| High | 99205 | 99215 |
| Minimal problem, may not require a physician | — | 99211 |
Consultation codes require a request for an opinion or advice from another qualified professional, the consultant's opinion, and a written report back to the requester. Medicare does not recognize consultation codes; for Medicare patients, report the appropriate office or hospital E/M code instead.
The Surgical Package
A CPT surgical code includes the operation plus typical preoperative and postoperative work: the E/M service after the decision for surgery (day before or day of surgery for major procedures), local or topical anesthesia, immediate postoperative care, writing orders, evaluating the patient in recovery, and typical follow-up care during the global period. Medicare global periods are 0, 10, or 90 days.
| Modifier | Use |
|---|---|
| 24 | Unrelated E/M service by the same physician during a postoperative period |
| 25 | Significant, separately identifiable E/M service on the same day as a procedure |
| 51 | Multiple procedures at the same session (not used with add-on codes or 51-exempt codes) |
| 57 | Decision for surgery made at an E/M service the day before or day of a major procedure |
| 58 | Staged or related procedure during the postoperative period |
| 59 / XE, XS, XP, XU | Distinct procedural service: separate encounter, structure, practitioner, or unusual non-overlapping service |
| 76 / 77 | Repeat procedure by the same / another physician |
| 78 | Unplanned return to the operating room for a related procedure during the postoperative period |
| 79 | Unrelated procedure during the postoperative period |
| 26 / TC | Professional component only / technical component only |
| 50 | Bilateral procedure |
| LT, RT, F1–FA, T1–TA, E1–E4 | HCPCS anatomic modifiers for side, fingers, toes, and eyelids |
HCPCS Level II
HCPCS Level II codes are one letter followed by four digits. They describe products, supplies, and services not in CPT: ambulance services and medical and surgical supplies (A codes), drugs administered other than by oral method (J codes, reported in units that match the dosage in the code descriptor), durable medical equipment (E codes), orthotics and prosthetics (L codes), and temporary codes (G, K, Q, S). HCPCS modifiers are two characters and may be alphabetic or alphanumeric.
Clinical Vocabularies and Terminologies
| Terminology | Purpose |
|---|---|
| SNOMED CT | Clinical terminology used inside the EHR to record problems, findings, and procedures; mapped to ICD-10-CM for reporting |
| LOINC | Identifies laboratory tests and clinical observations |
| RxNorm | Normalized names for clinical drugs |
| DSM-5-TR | Diagnostic criteria for mental disorders; crosswalks to ICD-10-CM codes |
| NDC | National Drug Code identifying drug products in pharmacy transactions |
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