What Are Drg Codes Diagnosis Related Groups Explained?

Diagnosis Related Groups (DRG) codes are a system Medicare and many private insurers use to classify hospital stays into payment categories. Each DRG represents a group of patients with similar medical conditions and expected resource use. The DRG assigned to a hospital stay determines the fixed amount the hospital gets paid, regardless of the actual costs incurred.

How Do DRG Codes Work?

DRG codes work like a pricing catalog for hospital visits. When a patient is discharged, the hospital assigns a DRG based on the patient’s principal diagnosis, secondary diagnoses, procedures performed, age, sex, and discharge status. Each DRG has a relative weight that reflects the average resources needed for that type of patient. Hospitals are then paid a fixed amount per case, adjusted by the hospital’s location and other factors.

This fixed payment system is called prospective payment. It was designed to replace the earlier system where hospitals were paid for each service they provided. Under the old system, hospitals had an incentive to do more tests and procedures. Under DRGs, if a hospital can treat a patient at a cost lower than the DRG payment, it keeps the difference. If costs exceed the payment, the hospital absorbs the loss.

What Is the Difference Between DRG Codes and ICD-10 Codes?

ICD-10 codes are the medical classification system used to describe specific diseases, injuries, and procedures. A patient’s hospital stay will have one principal ICD-10 diagnosis code and often several secondary codes. DRG codes are built from these ICD-10 codes, but they are a separate system. DRG codes group patients into broader categories for payment purposes. For example, many different ICD-10 pneumonia codes can map to the same DRG for pneumonia. Think of ICD-10 as the detailed medical vocabulary and DRG as the payment language that groups similar clinical cases together.

Why Were DRG Codes Created?

DRG codes were created to control rising hospital costs under Medicare. Before the DRG system, Medicare paid hospitals based on their reported costs. This gave hospitals little reason to limit services. Costs rose rapidly throughout the 1970s and early 1980s. In 1983, Congress introduced the Inpatient Prospective Payment System (IPPS) using DRGs. The goal was to pay a standard price for each case, encouraging hospitals to become more efficient without sacrificing quality. The system was later adopted by many state Medicaid programs and private insurers.

The evidence shows the DRG system succeeded in slowing the growth of hospital spending per case. However, it also created new incentives. Some hospitals responded by discharging patients earlier, by shifting certain procedures to outpatient settings, and by avoiding patients whose expected costs were high relative to the fixed payment. Researchers continue to study these trade-offs.

How Do DRG Codes Affect Hospital Care and Costs?

DRG codes directly shape the financial incentives hospitals face. Because payment is fixed per case, hospitals have a strong reason to reduce length of stay, avoid unnecessary testing, and streamline care pathways. This can potentially lower overall health care costs. At the same time, critics point out that DRG-based payment may encourage hospitals to select patients who are less expensive to treat, or to discharge patients “quicker and sicker.” Studies have shown that average hospital lengths of stay did drop after the DRG system was introduced. Whether quality of care suffered overall is debated, with some studies finding no major harm and others detecting increased readmission rates for certain conditions.

For patients, DRG codes rarely appear on a personal bill. When you receive a hospital bill, you see charges for each service, but the actual payment your insurance makes is based largely on the DRG. The amount you owe in coinsurance or deductibles may be linked to hospital charges, which can differ from the DRG payment. But the hospital’s focus on your DRG can influence how quickly you are discharged, what tests are done, and whether certain expensive treatments are offered.

What Are the Main Types of DRG Systems?

There are several types of DRG systems in use. The most common in the United States is the Medicare Severity DRG (MS-DRG) system, used by Medicare for inpatient hospital payments starting in 2008. MS-DRGs split many older DRGs into three severity levels: without complications or comorbidities (CC), with CC, and with major CC (MCC). This adjustment was meant to better account for patient complexity.

Another widely used system is the All Patient Refined DRG (APR-DRG). It is often used by private insurers and state Medicaid programs. APR-DRGs further adjust for severity of illness and risk of mortality, using four subclasses. They are considered more granular than MS-DRGs for rating patient complexity. Other variants include the All Patient DRG (AP-DRG) used in some states before APR-DRG adoption. Internationally, many countries have developed their own DRG-like systems, such as the Australian AR-DRG and the German G-DRG. All share the core idea: group similar cases and pay a fixed amount.

How Are DRG Codes Assigned to a Patient?

DRG assignment is not done by a doctor during the hospital stay but by a specially trained coder after discharge. The coder reviews the entire medical record and extracts all documented diagnoses and procedures. These are coded in ICD-10. A software program called a grouper then takes those ICD-10 codes plus patient age, sex, and discharge status (discharged home, transferred to another facility, died, etc.) and assigns the appropriate DRG. The assignment can be audited by Medicare or other payers. Errors in documentation or coding can lead to incorrect DRG assignment and either underpayment or overpayment. This is why hospitals invest heavily in clinical documentation improvement programs.

A critical factor in DRG assignment is whether a secondary diagnosis qualifies as a complication or comorbidity (CC) or a major complication or comorbidity (MCC). A patient with the same principal diagnosis but with an MCC will fall into a higher-paying DRG because the expected resource use is greater. This creates a financial incentive for hospitals to thoroughly document all relevant conditions, even those not directly related to the main reason for admission.

Do DRG Codes Affect My Hospital Bill or Insurance?

DRG codes determine what the hospital is paid by your insurer, not what you are billed. However, they can indirectly affect your out-of-pocket costs. Many health insurance plans calculate patient cost-sharing based on a percentage of hospital charges (as opposed to the DRG payment). If you have coinsurance, your share is a percentage of the hospital’s billed charges, which are typically much higher than the DRG payment. In that case, your personal cost is driven by charges, not the DRG. But if your insurance has a fixed copay for inpatient stays, the DRG does not directly change that copay amount.

Another indirect effect: because hospitals are paid a fixed amount per DRG, they may adopt policies that influence your care, such as shorter stays or more careful use of expensive tests. This could affect your experience but is not something you will see on a statement. If you have a Medicare supplement (Medigap) or a plan with a fixed daily copay, your costs are fairly predictable. In all cases, your explanation of benefits (EOB) will list the DRG code assigned to your stay, even though the hospital’s total charges are often also shown.