Medical billing involves dozens of specialized processes, but few are as directly connected to hospital revenue as DRG review. For hospital administrators, revenue cycle managers, and healthcare finance professionals, understanding what DRG review is — and why it matters — is essential for maintaining accurate reimbursements and avoiding costly compliance issues.

This guide explains DRG review in plain terms, covers why errors occur, and outlines how a structured DRG review process protects hospital revenue.

What Is a DRG?

DRG stands for Diagnosis-Related Group. It is a patient classification system used primarily by Medicare — and widely adopted by Medicaid and commercial payers — to determine how much a hospital will be reimbursed for an inpatient stay.

Instead of paying hospitals based on the individual services rendered during a stay, payers using DRG-based reimbursement assign each inpatient case to a specific DRG category. That category carries a fixed payment rate — regardless of how long the patient stays or how many individual services were provided.

The DRG assigned to a patient case is determined by a combination of factors including the primary diagnosis, secondary diagnoses, procedures performed, patient age, sex, and discharge status. Each of these variables influences the final DRG classification — and therefore the payment the hospital receives.

Because a single DRG assignment determines the entire reimbursement for an inpatient stay, accuracy matters enormously. A miscoded diagnosis, a missing comorbidity, or an incorrectly documented procedure can result in the wrong DRG being assigned — and the wrong payment being issued.

What Is DRG Review?

DRG review is the process of evaluating a patient's clinical documentation, diagnosis codes, procedure codes, and DRG assignment to verify that the classification accurately reflects the complexity and nature of the care provided.

In practical terms, DRG review involves a detailed examination of the medical record — including physician notes, operative reports, discharge summaries, and diagnostic findings — to confirm that every clinically significant diagnosis and procedure has been captured and coded correctly.

When DRG review identifies a discrepancy between what was documented and what was coded, the coding can be corrected before the claim is submitted — or an appeal can be filed if the claim has already been processed at an incorrect rate.

DRG review can be conducted prospectively — before claim submission — to prevent errors from reaching the payer. It can also be conducted retrospectively — after payment — to identify underpayments and support recovery efforts.

Why DRG Errors Happen

DRG miscoding is more common than many healthcare organizations realize. The most frequent causes include the following.

Incomplete Clinical Documentation

The most common root cause of DRG errors is incomplete or imprecise physician documentation. When a physician's notes do not clearly capture the full severity of a patient's condition — including all relevant comorbidities and complications — coders do not have the clinical basis to assign the correct codes. The result is a lower-complexity DRG and a reduced reimbursement.

Missed Comorbidities and Complications

Comorbidities and complications — known in coding terminology as CCs and MCCs — significantly affect DRG assignment. A patient with a principal diagnosis of pneumonia who also has sepsis, respiratory failure, or heart failure will be assigned a different — and higher-paying — DRG than a patient with uncomplicated pneumonia. If these secondary conditions are not clearly documented and coded, the higher-complexity DRG is missed entirely.

Coding Errors and Outdated Code Sets

ICD-10-CM and ICD-10-PCS code sets are updated annually. Coders who are not current with the latest code updates may assign outdated or incorrect codes that result in incorrect DRG assignments. Even minor coding errors — a wrong digit in a procedure code, a missing specificity indicator in a diagnosis code — can shift a case to a different DRG category.

Principal Diagnosis Selection Errors

The principal diagnosis — defined as the condition established after study to be chiefly responsible for the patient's admission — is a critical determinant of DRG assignment. Selecting the wrong principal diagnosis can move a case into an entirely different DRG group, often at a significantly lower reimbursement rate.

Lack of Coder-Physician Query Processes

When documentation is ambiguous or incomplete, coders need a process for querying physicians to clarify clinical findings. Organizations without a structured physician query process frequently leave DRG-impacting conditions undocumented and uncoded.

How DRG Errors Impact Hospital Reimbursement

The financial impact of DRG errors is direct and measurable. Every case assigned to the wrong DRG receives incorrect payment — either too low or, in some cases, too high.

Underpayment is the most common financial consequence. When a patient's condition is more complex than the assigned DRG reflects, the hospital receives less than it is entitled to for the care it provided. Across hundreds or thousands of inpatient cases per year, even small per-case underpayments accumulate into significant revenue losses.

Overpayment carries different risks. When a DRG is coded at a higher complexity than clinical documentation supports, the hospital may receive more than appropriate. This creates compliance exposure — payers conduct their own audits, and overpayments discovered during external review can result in repayment demands, penalties, and increased audit scrutiny going forward.

Both outcomes underscore why accurate DRG assignment — neither under-coding nor over-coding — is essential for financial and compliance performance.

What DRG Review Covers

A comprehensive DRG review examines every element that influences DRG assignment.

Clinical documentation is reviewed to confirm that all diagnoses, procedures, and clinical findings are clearly and completely documented in the medical record. Diagnosis code selection is evaluated to ensure that the principal diagnosis, secondary diagnoses, and all relevant comorbidities and complications are coded correctly using current ICD-10-CM codes. Procedure code selection is reviewed to verify that all significant inpatient procedures are captured using accurate ICD-10-PCS codes. DRG grouper logic is applied to confirm that the combination of codes produces the correct DRG assignment. And discharge status coding is checked, since incorrect discharge disposition codes can affect both DRG assignment and post-acute care payment.

The Connection Between DRG Review and Compliance

DRG review is not only a revenue protection tool — it is a compliance requirement. Medicare and other federal payers regularly conduct Recovery Audit Contractor (RAC) audits and other post-payment reviews specifically designed to identify DRG miscoding.

When RAC auditors identify DRG errors that resulted in overpayment, hospitals are required to repay the excess amount — often with additional scrutiny applied to future claims. Patterns of DRG miscoding, even when unintentional, can attract sustained audit attention that is costly and disruptive.

A proactive internal DRG review program addresses compliance risk before external auditors find the same issues. Organizations that conduct regular DRG audits are better prepared for RAC reviews, Medicare Administrative Contractor audits, and commercial payer audits — because they have already identified and corrected their own coding vulnerabilities.

Who Needs DRG Review Services

DRG review services are most valuable for healthcare organizations that handle significant volumes of inpatient cases billed under Medicare, Medicaid, or commercial payer contracts that use DRG-based reimbursement.

Hospitals and health systems of all sizes benefit from regular DRG review — particularly those with complex patient populations, high proportions of surgical cases, or significant volumes of cases involving comorbidities and complications. Academic medical centers and teaching hospitals, which frequently treat high-acuity patients, have particularly high exposure to DRG miscoding risk. Critical access hospitals and rural health facilities may lack in-house coding expertise at the depth required for complex DRG validation, making external review services especially valuable.

How Professional DRG Review Services Improve Reimbursement

Professional DRG review services — such as those provided by Patriot MedBill — bring specialized coding expertise, current knowledge of ICD-10 and DRG grouper updates, and a systematic review methodology that most internal billing departments cannot replicate on their own.

External DRG review specialists evaluate clinical documentation and coding from an objective perspective, identifying both underpayment opportunities and compliance risks that internal teams may overlook. They work directly with coding and clinical documentation improvement teams to close documentation gaps, correct coding errors, and establish physician query processes that prevent recurring issues.

The result is a more accurate coding operation, stronger DRG assignments, and reimbursements that consistently reflect the true complexity of the care provided.

Key Takeaways

DRG review is a foundational component of hospital revenue cycle management. It ensures that the single most important variable in inpatient reimbursement — the DRG assignment — accurately reflects the patient's clinical complexity and the care the hospital provided.

For hospitals and health systems managing significant inpatient volumes, regular DRG review is not optional — it is a financial and compliance necessity. Patriot MedBill's medical chart auditing and DRG review services are designed to identify coding errors, recover underpayments, and protect healthcare organizations from compliance risk.