ICD-10-CM Interview Questions & Advanced Coding
Beginner Questions
What is the difference between ICD-10-CM and ICD-10-PCS?
ICD-10-CM (Clinical Modification) is used to code diagnoses — what the patient has. It's used by all healthcare settings: physician offices, hospitals, outpatient facilities. ICD-10-PCS (Procedure Coding System) is used to code inpatient procedures — what was done to the patient in a hospital setting. PCS is only used for hospital inpatient claims. Outpatient procedures use CPT codes.
What does "code to the highest level of specificity" mean?
Always use the most specific code available that is supported by the documentation. If a code has 4, 5, 6, or 7 characters available, you must use all required characters. Choosing a less specific code when a more specific one exists is called "undercoding" and can result in claim denials and compliance issues. Example: M79.3 is "Panniculitis, unspecified" — if the documentation specifies the site, you must code to the site-specific code.
What is the significance of the first-listed diagnosis in outpatient coding?
For outpatient encounters, the first-listed diagnosis (not "principal diagnosis" — that term is only for inpatient) is the condition established to be chiefly responsible for the visit. In outpatient, do NOT code "probable" or "suspected" diagnoses — only code confirmed conditions or the symptom/sign. The first-listed diagnosis drives reimbursement and reporting.
Intermediate Questions
Explain the coding for diabetes mellitus with complications.
Diabetes codes are combination codes — one code captures both the diabetes type AND the complication. Key rules:
What is the sequencing rule for sepsis?
Sepsis sequencing is a high-stakes coding scenario:
Sepsis as principal diagnosis:
Sepsis present on admission with a localized infection:
Severe sepsis: Code A41.xx + R65.20 (Severe sepsis without septic shock) OR R65.21 (with septic shock)
Critical rule: Never code "urosepsis" — it is not an accepted term. Query the physician.
When do you use Z codes?
Z codes (Z00-Z99) classify factors influencing health status when no illness or injury is present, or to provide additional information:
Key rules for Z codes:
Advanced Questions
Explain POA (Present on Admission) reporting.
POA indicates whether a diagnosis was present at the time of inpatient admission. CMS requires POA reporting on Medicare/Medicaid inpatient claims to distinguish hospital-acquired conditions (HACs) from pre-existing ones.
| POA Indicator | Meaning |
|---|
|--------------|---------|
| **Y** | Present at the time of admission |
|---|---|
| N | Not present at time of admission |
| U | Documentation insufficient to determine |
| W | Provider is unable to clinically determine |
| 1 | Exempt from POA reporting (Z codes, injuries, etc.) |
Why it matters: CMS does not pay the higher DRG rate for HACs that are not POA. For example, a pressure ulcer that developed during the hospital stay (N) will not increase reimbursement — but a pressure ulcer present on admission (Y) can be counted.
Code this complex case:
"65-year-old female admitted with acute exacerbation of COPD. She is a current smoker. She also has stage 3 CKD secondary to hypertension. Blood pressure is 168/94 on admission. Chest X-ray shows right lower lobe pneumonia. She is on insulin for her Type 2 diabetes."
What is the difference between Excludes1 and Excludes2?
This is one of the most tested concepts:
Excludes1 — Mutually exclusive. The two conditions CANNOT occur together (they are the same condition). Do NOT use both codes.
Excludes2 — The excluded condition is NOT included in this code, but may coexist. CAN use both codes if both conditions are documented.
Memory trick:
Coding Practice Cases
Case 1: Patient with chest pain, rule out MI. Tests negative, final diagnosis: Chest pain due to GERD.
Answer: R07.9 Chest pain, unspecified is WRONG. The final diagnosis is GERD (K21.9). Code the confirmed diagnosis, not the symptom. The "rule out MI" is not coded — outpatient rule.
Case 2: Patient presents with infected diabetic foot ulcer, Type 2 DM, insulin-dependent.
Case 3: Outpatient encounter. Documentation: "Probable UTI."
Answer: Do NOT code N39.0 (UTI) for outpatient. Code the symptom instead: R30.0 (Dysuria), R35.0 (Frequency), or whatever symptom brought the patient in. "Probable" diagnoses are INPATIENT only.