6.2 Medical Coding Basics: ICD-10, CPT, and HCPCS
Key Takeaways
- ICD-10-CM codes report diagnoses ("why" the patient was seen) and are required on all insurance claims
- CPT codes report procedures and services ("what" was done) and are maintained by the American Medical Association (AMA)
- HCPCS Level II codes cover items not included in CPT, such as durable medical equipment, supplies, and ambulance services
- CMAAs do not typically assign codes but must understand coding basics to review encounter forms, verify claim accuracy, and communicate with billing staff
- Coding accuracy is essential for proper reimbursement — incorrect codes lead to claim denials, underpayment, or fraud allegations
- The provider is ultimately responsible for the accuracy of diagnosis and procedure codes
Medical Coding Basics: ICD-10, CPT, and HCPCS
While CMAAs are not coding specialists, understanding the basics of medical coding is essential for the CMAA exam and for supporting the billing process in the medical office.
The Three Main Coding Systems
| System | Full Name | Maintained By | Purpose |
|---|---|---|---|
| ICD-10-CM | International Classification of Diseases, 10th Revision, Clinical Modification | WHO (maintained by CMS for U.S.) | Reports diagnoses — why the patient was seen |
| CPT | Current Procedural Terminology | American Medical Association (AMA) | Reports procedures and services — what was done |
| HCPCS Level II | Healthcare Common Procedure Coding System | CMS | Reports supplies, equipment, and services not in CPT |
ICD-10-CM Diagnosis Codes
ICD-10-CM codes tell the insurance company why the patient received care. These codes justify the medical necessity of the services billed.
ICD-10-CM Code Structure
ICD-10-CM codes are 3-7 characters in length:
| Position | Content | Example |
|---|---|---|
| 1st character | Always a letter (A-Z, except U) | E (Endocrine, nutritional, metabolic) |
| 2nd-3rd characters | Numbers | E11 (Type 2 diabetes mellitus) |
| Decimal point | After the 3rd character | E11**.** |
| 4th-7th characters | Additional specificity | E11**.65** (Type 2 DM with hyperglycemia) |
Common ICD-10-CM Codes CMAAs Should Recognize
| Code | Diagnosis |
|---|---|
| Z00.00 | General adult medical examination (annual physical) |
| J06.9 | Acute upper respiratory infection, unspecified |
| I10 | Essential (primary) hypertension |
| E11.9 | Type 2 diabetes mellitus without complications |
| M54.5 | Low back pain |
| J20.9 | Acute bronchitis, unspecified |
| R50.9 | Fever, unspecified |
| Z23 | Encounter for immunization |
CPT Procedure Codes
CPT codes tell the insurance company what was done during the patient encounter. They are divided into three categories:
CPT Categories
| Category | Content | Code Range |
|---|---|---|
| Category I | Standard procedures and services | 00100-99499 (5-digit numeric) |
| Category II | Performance measurement/tracking | 0001F-9007F |
| Category III | Emerging technology/services | 0016T-0999T |
CPT Category I Sections
| Section | Code Range | Examples |
|---|---|---|
| Evaluation and Management (E/M) | 99201-99499 | Office visits, hospital visits, consultations |
| Anesthesia | 00100-01999 | Anesthesia for procedures |
| Surgery | 10004-69990 | All surgical procedures |
| Radiology | 70010-79999 | X-rays, CT, MRI, ultrasound |
| Pathology and Laboratory | 80047-89398 | Blood tests, urinalysis, biopsies |
| Medicine | 90281-99607 | Injections, EKGs, physical therapy, immunizations |
Common E/M Codes CMAAs Should Recognize
| Code | Description | Visit Type |
|---|---|---|
| 99213 | Established patient, low complexity | Brief follow-up visit |
| 99214 | Established patient, moderate complexity | Standard follow-up visit |
| 99215 | Established patient, high complexity | Complex follow-up visit |
| 99203 | New patient, low complexity | New patient brief visit |
| 99204 | New patient, moderate complexity | New patient standard visit |
| 99205 | New patient, high complexity | New patient complex visit |
| 99385-99397 | Preventive medicine (varies by age) | Annual physical/wellness visit |
CPT Modifiers
Modifiers are two-digit codes added to CPT codes to provide additional information:
| Modifier | Description |
|---|---|
| -25 | Significant, separately identifiable E/M service on the same day as a procedure |
| -59 | Distinct procedural service |
| -LT / -RT | Left side / Right side |
| -76 | Repeat procedure by the same physician |
| -TC | Technical component (facility charge for equipment/personnel) |
| -26 | Professional component (physician interpretation) |
HCPCS Level II Codes
HCPCS Level II codes cover items and services not included in CPT:
| Code Range | Category | Examples |
|---|---|---|
| A0000-A0999 | Transport/ambulance | Ambulance services |
| E0100-E8002 | DME (Durable Medical Equipment) | Wheelchairs, CPAP machines, hospital beds |
| J0100-J8999 | Drugs administered by provider | Injectable medications |
| L0100-L4999 | Orthotics/prosthetics | Braces, artificial limbs |
| K0001-K0900 | DME (temporary) | Temporary DME codes |
Coding and the CMAA Role
| CMAA Responsibility | Details |
|---|---|
| Encounter form review | Ensure the provider completed all sections of the superbill |
| Legibility check | Verify that handwritten codes/descriptions are readable |
| Routing | Route completed encounter forms to the billing/coding department |
| Communication | Relay coding questions from billing staff to the provider |
| Education | Understand coding basics to identify obvious errors (e.g., missing diagnosis code) |
Scope Reminder: CMAAs do not assign or change codes. The provider selects the diagnosis and procedure codes, and certified coders verify accuracy. If the CMAA notices a potential coding issue (e.g., a procedure code without a supporting diagnosis), they should flag it for the coder or provider.
ICD-10-CM codes are used to report:
Which CPT code range covers Evaluation and Management (E/M) services such as office visits?
A CMAA notices that the provider marked a procedure on the superbill but did not check a corresponding diagnosis code. What should the CMAA do?