How DRGs classify and bundle a stay
Under IPPS, an entire inpatient hospital stay, from admission to discharge, is classified into a single Diagnosis-Related Group (DRG) based on the patient's principal diagnosis, procedures performed, complications, and comorbidities. Rather than reimbursing each individual charge line on the bill, the facility is paid a single bundled amount tied to that DRG, regardless of how many individual services, supplies, or days of care were involved. This is a fundamentally different pricing model than line-by-line professional billing, since the DRG payment doesn't scale directly with the number or cost of billed line items.
Weight-based vs. flat-allowance DRG pricing
DRG pricing generally follows one of two structures. In a weight-based model, each DRG is assigned a relative weight reflecting the typical resource intensity of that diagnosis category, and the payment is calculated as DRG Weight × Conversion Factor (Base Rate). For example, a DRG with a weight of 6.778 and a base rate of $10,000 would produce a base payment of roughly $67,780, before other adjustments. In a flat-allowance model, a state instead publishes a fixed dollar allowance directly tied to the DRG or diagnosis category, without a separate weight-times-rate calculation. Knowing which structure a given state's workers' comp fee schedule uses is essential, since the two produce very different bill-level allowances even when both are described as "DRG-based" pricing.
Adjustments layered onto the base DRG payment
The base DRG payment is rarely the final allowed amount. Additional adjustments commonly applied on top include a hospital-specific wage index, which reflects local labor cost differences (commonly calculated as a blend such as (Base Allowance × 40%) + (Base Allowance × 60% × Wage Index)), teaching hospital adjustments, and outlier payments for unusually costly or lengthy stays that exceed a defined cost threshold for the assigned DRG. Missing any one of these adjustments can meaningfully understate or overstate the correct allowed amount for an inpatient stay.
Update cycles and state adoption dates
Medicare updates IPPS DRG weights and the associated base rate annually, effective October 1 of each year. States that reference IPPS for workers' comp inpatient pricing don't always adopt the update on that same date, and some states freeze DRG weights from an earlier federal fiscal year rather than updating annually. Correctly pricing an inpatient bill requires applying the DRG weight table, base rate, and wage index that were in effect, under the applicable state's adoption schedule, on the date of the admission, not simply the current Medicare values.
How BillSentry applies IPPS pricing
BillSentry automatically identifies the applicable workers' compensation reimbursement methodology and calculates the allowed amount at the bill-line level, including selecting the correct DRG, weight or flat-allowance value, wage index adjustment, and any applicable outlier calculation for the state and date of admission.
Every result is documented as a RuleTrace™, showing the DRG assignment, the weight or allowance used, and the full calculation behind the facility's bundled payment.