Denial codes, modifiers, HCPCS, CDT, and ICD-10 — explained in plain English with the fix, not just the definition. No login, no paywall. Type a code on any page to filter instantly, or use site search to find a code from anywhere.
What each denial code means, why it happens, and how to fix and prevent it — plus the CO/PR/OA group codes explained.
CO-45 · CO-97 · CO-197 · PR-204 · N130 🏷️When to use each modifier and the misuse patterns that trigger denials and audits — 25 vs 59, the X family, global period modifiers, ABN modifiers.
25 · 59 · XS · 26/TC · 50 · GA/GZ · KX 🦽Common DMEPOS codes with Medicare prior-auth flags, rental/purchase rules, and the documentation traps behind DME's high denial rates.
E0601 · K0823 · E1390 · A4253 · L0650 🦷High-volume dental codes with narrative requirements, frequency limits, and plan-clause traps — from prophy to implants.
D0120 · D2740 · D4341 · D6010 · D7210 🩻The diagnosis codes each specialty actually bills, with specificity rules and the medical-necessity pairings that keep claims clean.
F41.1 · E11.9 · M54.51 · G47.33 · M17.11 🗺️Medicaid and payer filing windows live in our state references — Texas's 95 days to Ohio's 365, plus national payer rows.
TX 95d · NY 90d · CA 6mo · Medicare 12moThe two-digit code that tells the payer where care happened — and quietly changes your payment rate. The ones that matter most:
| POS | Setting | Billing Notes |
|---|---|---|
| 11 | Office | The default for practice-based care; pays the non-facility (higher) rate for most services. |
| 02 | Telehealth — patient NOT at home | The 02 vs 10 split matters: rates and coverage differ. Pair correctly with modifier 95 per payer policy. |
| 10 | Telehealth — patient at home | Most home-based virtual visits belong here; using 11 for telehealth misrepresents the encounter. |
| 21 | Inpatient hospital | Facility rate applies — the professional claim pays less because the facility bills separately. |
| 22 | On-campus outpatient hospital | Facility rate; provider-based clinic visits here surprise practices that moved from POS 11. |
| 23 | Emergency department | ED E/M code family (99281–99285) expected; office codes at POS 23 reject. |
| 24 | Ambulatory surgical center | ASC procedure lists control what's payable; professional and facility claims must align. |
| 31 / 32 | Skilled nursing (Part A stay) / Nursing facility | 31 vs 32 changes consolidated billing — services during a Part A stay may belong to the SNF, not you. |
| 12 | Patient's home (in-person) | Home visits and home-delivered DME setup; supports home-health-adjacent services. |
These references grow based on what billers actually look up. If a code you need isn't here, email us the code — requested codes get added in the next update, and you'll get a direct answer in the meantime.