Coding and billing guides explain the rules that decide whether a claim gets paid: which CPT, HCPCS Level II and ICD-10-CM codes and modifiers to report, what Medicare, Medicaid and commercial payers require, and how a claim moves through the revenue cycle from prior authorization to payment posting.
This category is for billers, coders and practice managers who need code-level and payer-level detail. Coding topics include how to use unlisted CPT codes without triggering an audit, when a Category III code is the better choice than an unlisted code, what to enter in Box 19 of the CMS-1500, the GY modifier on Medicare cosmetic claims and when to use ICD-10-CM Z41.1. Billing workflow topics include the corrected claim resubmission process by payer type, 10-day and 90-day global period rules, billing Medicare as secondary under the CMS anti-markup rule and handling a Medicare MAC prepayment review. New to the field? Start with what medical billing is and how CPT codes work.
Coding & Billing FAQs
What is the difference between CPT and ICD-10-CM codes?
CPT codes, maintained by the American Medical Association, describe the procedures and services a provider performed. ICD-10-CM codes describe the diagnosis or reason for the encounter. Claims need both, linked correctly, so the payer can see that each service was medically necessary for the condition reported.
What is a corrected claim?
A corrected claim replaces or voids a claim the payer has already processed. On an 837P, it uses claim frequency code 7 (replacement) or 8 (void); on a paper CMS-1500, the code goes in Box 22 with the original claim number. Sending it as a new claim often triggers a duplicate denial.
Do commercial payers follow Medicare guidelines?
Not automatically. Many commercial payers adopt parts of Medicare’s approach, such as NCCI-style bundling edits or the CMS-1500 format, but their own contracts and published policies control payment. When a commercial policy is silent or unclear, call the payer and document the reference number and the answer you received.
Medical billing professionals who handle coordination of benefits claims frequently encounter a challenging scenario: a global imaging code such as CPT 74181 (MRI abdomen without contrast) was correctly billed and paid by a commercial primary insurer, but the claim must…
Every CPT code in the AMA’s procedural terminology system describes a specific, defined service. Most of the time, a provider can find a code that accurately fits what was performed. But medicine moves faster than codebooks.
When a provider bills an unlisted CPT code, there is no relative value unit attached to it. There is no national fee schedule rate. No automated adjudication system can price the claim because the code carries no defined descriptor.
When a provider performs a procedure that has no obvious home in the standard CPT code set, two options appear on the table.
When a claim lands on a payer reviewer’s desk with an unlisted procedure code in Box 24D, the reviewer does not open the attached operative report first. They read Box 19.
Medical necessity is the single most cited reason for claim denial across every payer type in the US healthcare system. The 2025 State of Claims report from Experian Health identified insufficient documentation as a top cause of denials, with denial…
Prior authorization denials for surgical procedures are the most expensive denial category in medical billing, not because individual claims are larger than other service types, but because the downstream consequences compound quickly.
A Medicare Administrative Contractor prepayment review is a formal medical record audit that occurs before Medicare pays a claim rather than after.
The Office of Inspector General of the US Department of Health and Human Services publishes and continuously updates a Work Plan that identifies the programs, services, and billing patterns it intends to audit.