Reference desk

Every rule that decides whether you get paid

Links go to the issuing body — CMS, NIH, NUCC, X12, your MAC — not to somebody's summary of it. If you bill from a summary, you are billing from an opinion.

Coverage policy — NCD, LCD and articles

This is where a denial is decided before you ever submit. LCDs are per-MAC, so the same CPT can be covered in one state and not the next.

Code sets — ICD-10-CM, CPT, HCPCS

Codes change every year. Billing from last year's set is a preventable denial.

Edits and modifiers — why a clean-looking claim still denies

NCCI and MUE reject claims that are individually correct but wrong together. This is the most common avoidable denial after eligibility.

What it actually pays

You cannot tell whether an underpayment happened without the fee schedule you were paid against.

Risk adjustment — HCC and RAF

In Medicare Advantage the plan is paid on RAF. A condition treated but never coded is revenue that silently never arrives.

Forms, EDI and identifiers

The transaction standards. Getting these wrong is a rejection, not a denial — it never reaches adjudication.

Rules that bite

Deadlines and consent requirements that void a claim regardless of how well it was coded.

Find your LCD — by state

An LCD is written by your Medicare Administrative Contractor, so coverage differs by state. A CPT payable in Texas can be denied in New York. Find your MAC, then read its LCD and — this is the part people skip — the billing and coding article attached to it, which carries the actual covered ICD-10 list.

Links are to public government and standards-body pages. CPT descriptors are AMA copyright and are not reproduced here. Nothing on this page is coding advice — it is where the rules live.