/icd10-cm

name: icd10-cm-skill
description: Extract billable ICD-10-CM diagnosis codes from a clinical note the way a professional coder builds the claim. Use when users say "code this encounter", "assign ICD-10 codes", "what diagnosis codes apply", "code this chart", or when turning clinical documentation into claim-ready diagnosis codes.

ICD-10-CM Coding from Clinical Notes

Turn a clinical note into the diagnosis codes a professional coder would submit on the claim for that encounter. This happens in two distinct steps: first decide *which* conditions belong on the claim, then find the *exact* code for each. Both steps cause errors: coders miss claims by listing the wrong conditions, and by coding the right condition at the wrong specificity.

Step 1: Decide what belongs on the claim

A claim reflects the encounter, not the patient's chart. Per the ICD-10-CM Official Guidelines for outpatient coding:

**Code, in this order:** 1. The reason for the visit (first-listed diagnosis). When the visit itself is for aftercare, screening, or follow-up, the Z-code IS the first-listed diagnosis — e.g. orthopedic aftercare/hardware removal (Z47.x), suture removal (Z48.02), a scheduled wellness exam (Z00.0x). 2. Conditions evaluated, managed, or treated at this visit — a medication refill or "stable, continue current plan" counts as managed. 3. Chronic comorbidities, but only if they were addressed or changed medical decision-making this visit.

**Symptoms:** when the patient came in FOR a symptom and the visit ends with no established diagnosis, that symptom is the first-listed diagnosis — code it (low back pain M54.5x, joint pain M25.5xx). That is the only time a symptom is coded. A symptom that accompanies a coded diagnosis (headache with a coded neck injury, dizziness with coded vertigo, fatigue with coded anemia) is part of that diagnosis and never coded separately.

**Leave off the claim:**

• Uncertain diagnoses — "probable", "suspected", "rule out". In outpatient coding these are never coded; code the presenting symptom instead.
• Conditions mentioned only as history and not treated today.
• Wellness-exam codes (Z00.0x) on a problem-focused visit. They belong only when the encounter is an actual scheduled physical.
• Status, lifestyle, and counseling codes — nicotine dependence (F17.x), alcohol use (F10.x), long-term medication (Z79.x), device/stent status (Z95.x), counseling (Z71.x) — unless that item is a substantial focus of the visit, not a passing mention or routine social-history line.
• External-cause codes (V00–Y99, how an injury happened): outpatient claims rarely carry them and most payers don't require them — the injury code itself carries the claim. Include them only when the setting or payer specifically requires external-cause reporting.

A correctly coded outpatient encounter is short — usually 1 to 4 codes. If your draft list is longer, you are coding the problem list rather than the encounter; cut anything that wasn't actually evaluated, managed, or treated this visit.

Step 2: Code at the documented specificity

This is where most miscoding happens. Two rules:

**Don't hedge on a diagnosis.** Never list sibling codes, candidate alternatives, or a category plus its children for the *same* diagnosis — commit to the single code the documentation supports for each. If you are torn between two codes for one diagnosis, the documentation is undetailed and the unspecified code wins.

**Code exactly what the note documents — never above it, never below it.**

• **Default to unspecified when the note doesn't subtype.** "Asthma" with no severity → J45.909. "Psoriatic arthritis" with no subtype → L40.50. "Type 2 diabetes" with no complication linked in the note → E11.9. "Hepatitis C" without documented chronicity → B19.20. Unspecified (.9, .50, .909) is the *correct* code for an undetailed note — it is not a fallback or a failure.
• **Do not infer** chronicity, severity grades, laterality, episode type, or diabetes-complication links that the note doesn't state. An ulcer coded with a severity character (L97.x1x "limited to breakdown of skin") requires the note to actually stage the depth; otherwise use unspecified severity (L97.x19).
• **A complication or subtype must be linked by the clinician, not assembled from data.** Lab values, vitals, and imaging findings in the note do not by themselves make a complication codable — an elevated A1c does not establish "T2DM with hyperglycemia," and an echo finding does not establish the heart-failure subtype, unless the clinician's own assessment states it. Code from the assessment wording; if the assessment names the condition without the complication, code it unspecified.
• **Add-on codes accompany their base code, never replace it.** Resistant hypertension I1A.0 is assigned in addition to I10; if you use an add-on, the base code stays on the claim.
• **"Other specified" (.8, .59) is not "unspecified."** Use it only when the note names a specific subtype that has no code of its own. No subtype documented → unspecified, not "other."
• **Never output a bare category.** J45, F32, E11, N20 alone are not billable codes. Every code must be carried to its full billable length.
• **Use the documentation when it IS specific.** "Acute on chronic systolic heart failure" → I50.23, not I50.9. Under-coding documented detail loses exactly as much as over-inferring.

Step 3: Find the exact code via the ICD-10 connector

Look up every diagnosis with the ICD-10 Codes connector's tools — **including diagnoses you're sure you know.** Code sets change every October and your memory of common codes can be stale; for example, "depression, unspecified" has been F32.A (not F32.9) since 2022. The connector has the current set; trust it over recall.

• Use `search_codes` with `code_type="diagnosis"`, building the query from the note's own wording plus the specificity decision from Step 2 — if you decided "unspecified," put "unspecified" in the search terms.
• Ta