Same Patients, New CMI: How MS-DRG V44.0 Shifts Case Mix
Your case mix index can move on October 1 without a single patient changing. MS-DRG V44.0 regroups some claims and reweights almost every DRG. Nationally the two effects cancel. At an individual hospital they usually do not.
We priced real Medicare volume under V43.1 and V44.0 to see who moves and why. The national answer is flat. The hospital answer depends almost entirely on how surgical your mix is.
Nationally, CMI Does Not Move
CMS publishes the FY 2025 MedPAR claims behind the FY 2027 weights grouped under both versions, in the AOR/BOR files that accompany the final rule. That makes the national comparison exact: the same 6,919,068 discharges, grouped and weighted each way.
| V43.1 | V44.0 | Change | |
|---|---|---|---|
| Discharges | 6,919,068 | 6,919,068 | 0 |
| Case mix index | 1.9554 | 1.9558 | +0.02% |
That is by design. CMS normalizes each year's weights so that recalibration alone does not raise or lower national case mix. Behind the flat national number, every gain was paid for by a loss somewhere else.
Medical DRGs Paid for Surgical Gains
Split the same claims into medical and surgical DRGs and the redistribution shows up.
| Discharges | Share of relative weight | RW per case, V43.1 | RW per case, V44.0 | Change | |
|---|---|---|---|---|---|
| Medical DRGs | 5,036,827 | 51.5% | 1.3832 | 1.3731 | -0.73% |
| Surgical DRGs | 1,882,241 | 48.5% | 3.4866 | 3.5150 | +0.82% |
Medical DRGs carry 73% of discharges, so a small cut per case adds up. The highest-volume medical DRGs mostly lost weight:
| DRG | Title | FY 2025 discharges | V43.1 | V44.0 | Change |
|---|---|---|---|---|---|
| 871 | Septicemia or Severe Sepsis without MV >96 Hours with MCC | 593,322 | 1.9425 | 1.9320 | -0.54% |
| 291 | Heart Failure and Shock with MCC | 305,005 | 1.2838 | 1.2685 | -1.19% |
| 193 | Simple Pneumonia and Pleurisy with MCC | 156,552 | 1.3144 | 1.2825 | -2.43% |
| 177 | Respiratory Infections and Inflammations with MCC | 111,752 | 1.5627 | 1.6092 | +2.98% |
| 872 | Septicemia or Severe Sepsis without MV >96 Hours without MCC | 105,706 | 1.0233 | 1.0066 | -1.63% |
| 189 | Pulmonary Edema and Respiratory Failure | 95,597 | 1.2354 | 1.2108 | -1.99% |
| 690 | Kidney and Urinary Tract Infections without MCC | 95,412 | 0.8095 | 0.8010 | -1.05% |
DRG 177 is the exception among the large ones. Otherwise the core of a community hospital's medical volume lost between half a percent and two and a half percent of relative weight.
Who Gains and Who Loses
To see how this lands on individual hospitals, we took each hospital's 2024 Medicare discharges by DRG from the CMS Medicare Inpatient Hospitals by Provider and Service file and priced them at V43.1 and V44.0 weights. We kept the 2,289 hospitals with at least 200 reported discharges.
The clearest pattern is how much of a hospital's volume is surgical:
| Surgical share of discharges | Hospitals | Median CMI change | Middle 80% |
|---|---|---|---|
| Under 10% | 805 | -0.60% | -0.82% to -0.40% |
| 10-20% | 740 | -0.38% | -0.54% to -0.15% |
| 20-30% | 418 | -0.13% | -0.35% to +0.14% |
| 30-40% | 212 | +0.12% | -0.17% to +0.56% |
| 40-50% | 48 | +0.41% | -0.09% to +1.07% |
| 50% and over | 66 | +1.57% | +0.23% to +3.24% |
Geography and size follow from that. Rural hospitals, which run more medical volume, came out worse than metropolitan ones: a median of -0.55% for micropolitan hospitals and -0.61% for small-town and rural ones, against -0.33% in metro cores. Hospitals reporting more than 5,000 Medicare discharges had a median of -0.08%. Those reporting 200 to 500 had a median of -0.56%.
The largest losses went to hospitals whose volume is concentrated in a single medical DRG family. DRG 945 (Rehabilitation with CC/MCC) fell 4.8%. A hospital whose reported Medicare volume is mostly rehabilitation stays loses CMI by about that much.
Treat the hospital figures as a ranking. CMS suppresses any hospital and DRG combination with fewer than 11 discharges, and that hides 41% of surgical discharges but only 23% of medical ones. Because surgical volume is the side that gained, the reported cells understate most hospitals' result. Run on the unsuppressed national totals, the same method gives +0.01% against the exact +0.02%. So the method holds, and the hospital estimates run about 0.1 to 0.2 points low. The ordering, with medical-heavy hospitals below surgical-heavy ones, does not depend on that.
Restructured Families Moved More Than Their Weights Suggest
Fourteen new DRGs and eighteen retirements change where cases land as well as what each DRG pays. For a hospital, the useful number is relative weight per case across the whole family before and after. These are the families that traded cases between versions, from the same national claims:
| DRG family | Discharges | RW per case, V43.1 | RW per case, V44.0 | Change |
|---|---|---|---|---|
| Spinal fusion except cervical | 108,640 | 4.7908 | 4.9542 | +3.41% |
| Male reproductive O.R. | 9,792 | 1.6300 | 1.6756 | +2.80% |
| Defibrillator, thrombolysis and other major cardiovascular | 43,708 | 4.4923 | 4.5986 | +2.37% |
| Hip, knee and other musculoskeletal surgery | 254,256 | 2.6317 | 2.6504 | +0.71% |
| Gynecologic O.R. | 14,996 | 1.8064 | 1.8090 | +0.14% |
| Pacemaker revision | 6,899 | 2.4411 | 2.4302 | -0.44% |
| Kidney and urinary O.R. | 52,430 | 1.6545 | 1.6410 | -0.82% |
| Endocrine O.R. | 35,938 | 2.3136 | 2.2855 | -1.21% |
| Other circulatory O.R. | 8,421 | 3.3406 | 3.2546 | -2.57% |
Spinal fusion: the surviving DRGs lost weight, the family gained
Read DRG by DRG, spinal fusion looks like a loser. DRG 426 fell 10.00%, the cap, and so did 457. DRG 427 fell 7.12%. A dashboard that tracks weights by DRG number would flag spine as a problem service line.
The family as a whole gained 3.41% per case. CMS moved 6,651 of the most complex fusions out of 426-428 and 456-458 into the new DRGs 523-525. DRG 523 carries a relative weight of 13.7443. The old DRGs lost their most expensive cases, so their weights fell. The cases themselves are paid more than before.
The spinal fusion hospitals in our data gained the most of any group. Hospitals where fusion is more than 10% of Medicare volume had a median gain of +1.65%. One caveat on the method: the provider file counts discharges by DRG, not by claim, so we cannot see which of a hospital's fusions moved into 523-525. We applied the national family rate to every hospital. A program doing more multi-region fusions than average will gain more than that, and one doing fewer will gain less.
Hip and knee surgery: the family moved less than its cases did
The musculoskeletal surgery family gained 0.71% per case, but the cases inside it moved a long way. Most hip and knee revisions now group to the wound debridement DRGs 463-465 rather than the new revision DRG 449, and whether a revision gains or loses depends on how it was coded. We covered that in detail in Most Hip and Knee Revisions Now Group to Wound Debridement.
What to Do With This
- Restate last year before reporting a trend. Run your FY 2026 discharges through V44.0 and compare them with FY 2027 on the same grouper. Any CMI change you report without restating will mix real changes in acuity with the grouper's redistribution.
- Expect a lower CMI if your mix is medical. A community hospital with less than a fifth of its volume surgical should expect CMI to fall by around half a percent from weights alone. That is not a documentation problem, and CDI should not be asked to recover it.
- Track restructured service lines by family, not by DRG number. The spinal fusion DRGs that kept their numbers lost weight while the family gained. The same applies anywhere CMS split or merged DRGs.
- Price the shift in dollars. CMI moves your operating payment almost one for one. At $50 million in Medicare IPPS operating revenue, a 0.5% CMI change is about $250,000 a year with no change in patients.
Run Your Own Numbers
The MS-DRG grouper groups any claim under V43.1 and V44.0 from the version dropdown, and the same comparison works for a full year of discharges through the API. Group your last fiscal year both ways. The difference between the two CMIs is how much of next year's change was the grouper.
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National figures come from the FY 2027 IPPS final rule correction notice AOR/BOR files (FY 2025 MedPAR claims grouped under V43 and V44) and Table 5 relative weights. Hospital figures use the CMS Medicare Inpatient Hospitals by Provider and Service file for data year 2024. That year spans V41 and V42 numbering, so retired spinal fusion DRGs were mapped into the V43 family. Families that traded cases between versions keep each hospital's own severity mix and take the national change in relative weight per case. Relative weight is not payment: actual reimbursement also applies the wage index, capital, DSH and IME adjustments, and outlier payments.