Medical Billing, Coding and Denials: What Every Physician Should Understand

Physicians are trained in exhaustive detail on how to take a history, examine a patient and make a plan. Almost none are taught how that encounter becomes a payment. The Dark Side of Medicine describes the moment many new physicians meet this gap: the patient has left, the care was excellent, and now the claim has to be right. This guide explains the parts of the billing process every physician should understand, even if someone else submits the claims.

The revenue cycle in one page

The revenue cycle is everything between scheduling a patient and the practice being paid:

1. Scheduling and registration — capturing accurate demographics and insurance information.
2. Eligibility and benefits check — confirming active coverage, network status, copays and deductibles.
3. Prior authorization — obtaining approval in advance where the insurer requires it.
4. The visit and documentation — the note that supports everything that follows.
5. Coding and charge entry — translating the note into codes and charges.
6. Claim scrubbing and submission — checking claims against payer and national edits, then sending them electronically.
7. Payment posting — reconciling what each payer paid against what the contract says it should pay.
8. Denial management and appeals — fixing and resubmitting, or appealing.
9. Patient billing and collections — statements for deductibles, coinsurance and self-pay balances.

A weakness at any step shows up later as a denial or a slow payment. Most of the expensive problems start in the first three steps, before the patient is ever seen.

The codes you need to know

• CPT codes (Current Procedural Terminology), maintained by the American Medical Association, describe services and procedures: office visits, echocardiograms, catheterizations.
• HCPCS Level II codes cover items and services not in CPT, such as certain drugs, supplies and devices.
• ICD-10-CM codes describe diagnoses. They tell the payer why the service was medically necessary.
• Modifiers are two-character additions to a procedure code that explain special circumstances, such as a distinct procedural service or a professional component only.
• Place of service codes tell Medicare where the service occurred, for example an office or an outpatient hospital department. They affect how much is paid.

The book refers to the billing code as a “DRG code.” Strictly, diagnosis-related groups (DRGs) are how Medicare pays hospitals for inpatient stays. A physician's own services, even in the hospital, are billed with CPT and HCPCS codes on a professional claim (the CMS-1500 form or its electronic version, the 837P). The underlying point stands: the code you choose decides what you are paid.

Medicare and many other payers also apply the National Correct Coding Initiative (NCCI) edits, which flag code pairs that should not normally be billed together and set limits on how many units of a service can be billed per day. Knowing that these edits exist explains many “unbundling” denials.

Documentation is the foundation

“The homework doesn’t end just because the patient is out of the room”

Dr. Siddiqui argues that building a system matters more than memorizing codes. Review the chart before you walk in. Anticipate the level of care and the likely codes while you are with the patient. Then close the note promptly, while the details are fresh. Some physicians code immediately after each visit; others do it at the end of the day. Either works if it is consistent, but end-of-day coding when you are tired invites errors.

Coding accuracy cuts both ways. Under-coding leaves earned income unpaid. Over-coding, or billing for services the note does not support, creates repayment obligations and, in serious cases, liability under federal law, including the False Claims Act. The HHS Office of Inspector General publishes compliance program guidance that even a small practice can adapt: written policies, periodic audits, training and a clear way to fix problems when they are found.

Why claims are denied

Denial reasons cluster into familiar groups:

• Registration and eligibility errors: wrong member ID, inactive coverage, the wrong payer billed first.
• Missing prior authorization or a service that went beyond what was authorized.
• Coding problems: diagnosis codes that do not support medical necessity, NCCI edits, missing or incorrect modifiers.
• Missing information: referring provider, NPI, place of service, attachments the payer requested.
• Timely filing: claims submitted after the payer's deadline. For Medicare, claims generally must be filed within 12 months of the date of service; commercial contracts set their own, often shorter, limits.
• Credentialing gaps: services provided before your enrollment with that payer was effective.
• Duplicate claims and coordination-of-benefits disputes.

Prior authorization is a growing share of the burden. CMS's Interoperability and Prior Authorization final rule (CMS-0057-F) is phasing in requirements for Medicare Advantage, Medicaid and certain other plans to make decisions within set timeframes and to explain denials, with electronic prior authorization interfaces to follow. Commercial plans not covered by that rule set their own processes.

Working denials and appeals

Every denial carries a reason code. Group denials by reason each month and fix the cause upstream, not just the individual claim. A denial that recurs is a process problem.

When a denial is wrong, appeal it. Traditional Medicare has a five-level appeals process, beginning with a redetermination by the Medicare Administrative Contractor and continuing to independent reconsideration, an administrative law judge, the Medicare Appeals Council and federal court. Each level has filing deadlines. Commercial payers have their own appeal procedures, set out in your contract and provider manual, and many states regulate them.

Patients are protected too. The federal No Surprises Act limits surprise bills for certain out-of-network emergency care and for some out-of-network care at in-network facilities, and requires good-faith cost estimates for uninsured or self-pay patients. Make sure your front office understands those rules.

Keep a simple denial log that records the payer, the reason code, who fixed it and how long it took. After a few months, the log shows where training, templates or front-desk checklists need to change.

In-house billing or a billing company?

Dr. Siddiqui's own clinic used a third-party billing company, and he recommends the approach. A good billing service brings trained coders, a “scrubber” who checks each claim for missing components before it goes out, and software that tracks every claim. An in-house biller gives you closer control and faster answers. Either way:

• Get a written agreement that defines duties, reporting, data access and what happens to your data if you part ways.
• Be cautious about fee structures and make sure the arrangement is reviewed by counsel; you remain legally responsible for claims under your NPI.
• Insist on monthly reports: charges, collections, denial rate by reason and payer, clean-claim rate, and accounts receivable by age.
• Compare what each payer actually pays with your contracted rates. Underpayments are common and often go unnoticed.

Educational information only — not legal, financial, tax or billing advice. Consult qualified advisors. Laws and payer rules differ by state and change often; the descriptions here are general.