Key facts for DRG 642
- FY2027 relative weight
- 1.3230
- Higher than 36% of all MS-DRGs
- Change vs FY2026
- -7.0%
- FY2026 weight 1.4220
- Geometric mean LOS
- 3.2 days
- Arithmetic mean 4.5 days
- MDC
- 10
- Assignment of Diagnosis Codes
- Severity level
- single severity level
- Transfer policy
- Not a transfer DRG
TL;DR
MS-DRG 642 is a medical group in MDC 10 (Assignment of Diagnosis Codes) at a single-severity group of its family. CMS assigns it a FY2027 relative weight of 1.3230 with a geometric mean length of stay of 3.2 days and an arithmetic mean of 4.5. Its weight moved down 7.0% from FY2026 (1.4220). That weight is higher than 36% of all medical and surgical MS-DRGs. CMS does not split this group by severity. The v44 Definitions Manual assigns it through 216 principal diagnosis codes.
What changed from FY2026 to FY2027
CMS recalibrates every MS-DRG weight annually from the prior year's MedPAR claims. For DRG 642 the FY2027 relative weight is 1.3230 against 1.4220 in FY2026, a fall of 6.96%, which exceeds the 2% threshold worth re-checking in contract models.
| Metric | FY2026 | FY2027 | Change |
|---|---|---|---|
| Relative weight | 1.4220 | 1.3230 | -0.0990 |
| Geometric mean LOS (days) | 3.4 | 3.2 | -0.2 |
| Arithmetic mean LOS (days) | 4.6 | 4.5 | -0.1 |
CC and MCC family
DRG 642 stands alone: CMS does not split this base group by CC or MCC severity, so complication documentation does not move the assignment, although it still affects quality and risk-adjustment reporting.
Grouper logic (v44 Definitions Manual)
Principal Diagnosis: 216 ICD-10 codes drive assignment to this group; the first 12 are shown.
| ICD-10 code | Description |
|---|---|
| C965 | Multifocal and unisystemic Langerhans-cell histiocytosis |
| C966 | Unifocal Langerhans-cell histiocytosis |
| D8130 | Adenosine deaminase deficiency, unspecified |
| D8131 | Severe combined immunodeficiency due to adenosine deaminase deficiency |
| D8132 | Adenosine deaminase 2 deficiency |
| D8139 | Other adenosine deaminase deficiency |
| D815 | Purine nucleoside phosphorylase [PNP] deficiency |
| D81810 | Biotinidase deficiency |
| D841 | Defects in the complement system |
| E700 | Classical phenylketonuria |
| E701 | Other hyperphenylalaninemias |
| E7020 | Disorder of tyrosine metabolism, unspecified |
Documentation and denial exposure
As a medical DRG, assignment depends on the principal diagnosis sequenced from the attending's documentation; a secondary condition sequenced first, or a symptom code in place of the confirmed diagnosis, changes the MDC or the DRG. Because this family has no severity split, review risk concentrates on medical-necessity of the admission itself and on the two-midnight benchmark. Typical inpatient denial codes for this group: CARC 16 (claim lacks information needed to group the stay), CARC 50 (the admission or procedure is judged not medically necessary), CARC 97 (a service is bundled into the DRG payment).
How QuickIntell uses DRG 642 data
QuickCode groups inpatient encounters against the current v44 logic, flags CC and MCC candidates that lack supporting documentation, and shows the weight difference across the family before the claim drops. QuickScribe captures the attending's language that supports severity, and QuickRCM works DRG-validation denials with the grouper evidence attached.
Frequently asked questions — DRG 642
What is MS-DRG 642?
MS-DRG 642 is "Inborn and Other Disorders of Metabolism", a medical Medicare Severity Diagnosis-Related Group in MDC 10, Assignment of Diagnosis Codes. Medicare pays inpatient stays grouped here at the hospital's base rate multiplied by the DRG relative weight.
What is the FY2027 relative weight for DRG 642?
The FY2027 relative weight is 1.3230 (IPPS final rule Table 5, effective October 1, 2026). In FY2026 it was 1.4220, a change of -7.0%.
What is the average length of stay for DRG 642?
CMS reports a geometric mean length of stay of 3.2 days and an arithmetic mean of 4.5 days for FY2027. The geometric mean is used for transfer-payment calculations.
What documentation supports the severity level of DRG 642?
DRG 642 has no CC or MCC sibling, so secondary-diagnosis capture does not change the group or its weight. Review effort belongs instead on the principal diagnosis sequencing and the procedure codes that place the stay in this group, and on medical necessity of the inpatient admission itself under the two-midnight benchmark, which is where denials for single-severity groups concentrate.
Which codes group to DRG 642?
The v44 Definitions Manual lists 216 principal diagnosis codes for this group. Examples from the principal diagnosis list: C965 (Multifocal and unisystemic Langerhans-cell histiocytosis); C966 (Unifocal Langerhans-cell histiocytosis); D8130 (Adenosine deaminase deficiency, unspecified); D8131 (Severe combined immunodeficiency due to adenosine deaminase deficiency).
Is DRG 642 a post-acute transfer DRG?
No. DRG 642 is not on the FY2027 post-acute care transfer list, so the transfer per-diem policy does not apply to it.
Sources
Every figure on this page is taken from the CMS publications below, as released by the Centers for Medicare & Medicaid Services. Projection built 2026-10-01. Verify against the primary file before billing or contracting decisions.
- IPPS FY2027 Final Rule Table 5 (CMS-1849-F)Version v44 FY2027 · effective 2026-10-01 · file CMS-1849-F Table 5.txtSHA-256 01003dd571c1e2f5…
- IPPS FY2026 Final Rule Table 5 (CMS-1833-F)Version v43 FY2026 · effective 2025-10-01 · file CMS-1833-F Table 5.txtSHA-256 bf8c390d14b3cd3e…
- ICD-10 MS-DRG Definitions Manual v44 (text)Version v44 · effective 2026-10-01 · file fy2027-fr-icd10-ms-drg-definitions-manual-files-v44.zipSHA-256 ae4f6c11727fe91f…
Disclaimer
This page is an operational reference compiled from the CMS IPPS FY2027 final rule (Table 5) and the v44 ICD-10 MS-DRG Definitions Manual. Relative weights are national factors; actual payment depends on each hospital's wage-adjusted base rate, add-ons, outliers and transfer adjustments. Nothing here is legal, clinical or billing advice; verify grouping against your encoder and the published CMS files.