Medical Billing & Coding Fundamentals

01ICD-10, CPT, and HCPCS — What Each Codes

ICD-10-CM codes explain WHY a service was provided (the diagnosis). CPT codes explain WHAT was done (the procedure or service, like an office visit or surgery). HCPCS Level II codes cover supplies, equipment, and services — like ambulance transport or durable medical equipment — that fall outside CPT's scope.

02Clearinghouses

A clearinghouse sits between the provider and the payer, scrubbing/validating claims for formatting and data errors (like a missing NPI or invalid ID) before forwarding them to the insurance company, catching easily fixable mistakes early.

03Denial vs. Rejection

A rejection happens before the payer processes the claim — it failed clearinghouse or payer validation due to something like a typo or missing field, and is usually fixed and resubmitted within hours. A denial happens after the payer fully processes the claim and decides not to pay it (e.g., not medically necessary, not covered), which requires a formal appeal.

04Modifiers

A modifier is a code appended to a CPT/HCPCS code to indicate a procedure was altered in some way — for example, that two normally-bundled services were actually distinct and separately billable on the same day — without changing the underlying code's definition.

05Upcoding & Unbundling as Fraud

Upcoding is billing a higher-level, more expensive code than what was actually performed or documented. Unbundling is separately billing components of a procedure that should be reported together under one comprehensive code. Both are considered healthcare fraud and can violate the False Claims Act.

06EOB, ERA, and Timely Filing

An EOB (Explanation of Benefits) is the payer's summary of what was covered and paid, often mailed and taking weeks to arrive. An ERA (Electronic Remittance Advice) is its electronic equivalent, delivered instantly into the practice's billing system. Timely filing limits are payer-set deadlines for submitting claims (and appealing denials) — miss them and the claim can be denied regardless of medical merit.