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MS-DRG 599 · MDC 09 · Medical

MS-DRG 599: Malignant Breast Disorders without CC/MCC

Reviewed by QuickIntell RCM Editorial Team · Last reviewed

Data effective
Data currency: IPPS Table 5 FY2027 final rule (effective October 1, 2026); Definitions Manual v44 (effective October 1, 2026). Next CMS release: April 1, 2027 (v44.1 mid-year update), then the FY2028 final rule in August 2027.

Key facts for DRG 599

FY2027 relative weight
0.6930
Higher than 5% of all MS-DRGs
Change vs FY2026
-9.9%
FY2026 weight 0.7690
Geometric mean LOS
1.8 days
Arithmetic mean 2.2 days
MDC
09
Diseases and Disorders of the Skin, Subcutaneous Tissue and Breast
Severity level
without CC or MCC
Transfer policy
Not a transfer DRG

TL;DR

MS-DRG 599 is a medical group in MDC 09 (Diseases and Disorders of the Skin, Subcutaneous Tissue and Breast) at the base severity level of its family. CMS assigns it a FY2027 relative weight of 0.6930 with a geometric mean length of stay of 1.8 days and an arithmetic mean of 2.2. Its weight moved down 9.9% from FY2026 (0.7690). That weight is higher than 5% of all medical and surgical MS-DRGs. Its CC/MCC family (DRG 597, DRG 598) spans weights 0.6930 to 1.7380. The v44 Definitions Manual assigns it through 74 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 599 the FY2027 relative weight is 0.6930 against 0.7690 in FY2026, a fall of 9.88%, which exceeds the 2% threshold worth re-checking in contract models.

FY2026 versus FY2027 payment factors for MS-DRG 599
MetricFY2026FY2027Change
Relative weight0.76900.6930-0.0760
Geometric mean LOS (days)2.41.8-0.6
Arithmetic mean LOS (days)2.82.2-0.6
Weights shown are the FY2027 final values after the 10% cap on year-over-year reductions where applicable.

CC and MCC family

DRG 599 shares its base definition with 2 other MS-DRGs split by severity. The family's weights span 0.6930 to 1.7380, a 2.51× spread, which is the payment effect of documenting qualifying complications and comorbidities.

MS-DRGs in the same base group as DRG 599
DRGTitleFY2027 weightGMLOS
597Malignant Breast Disorders with MCC1.73804.8
598Malignant Breast Disorders with CC1.09603.3
599Malignant Breast Disorders without CC/MCC0.69301.8

Grouper logic (v44 Definitions Manual)

Principal Diagnosis: 74 ICD-10 codes drive assignment to this group; the first 12 are shown.

Principal Diagnosis codes assigned to DRG 599 (sample)
ICD-10 codeDescription
C50011Malignant neoplasm of nipple and areola, right female breast
C50012Malignant neoplasm of nipple and areola, left female breast
C50019Malignant neoplasm of nipple and areola, unspecified female breast
C50021Malignant neoplasm of nipple and areola, right male breast
C50022Malignant neoplasm of nipple and areola, left male breast
C50029Malignant neoplasm of nipple and areola, unspecified male breast
C50111Malignant neoplasm of central portion of right female breast
C50112Malignant neoplasm of central portion of left female breast
C50119Malignant neoplasm of central portion of unspecified female breast
C50121Malignant neoplasm of central portion of right male breast
C50122Malignant neoplasm of central portion of left male breast
C50129Malignant neoplasm of central portion of unspecified male breast

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 splits by severity, auditors target CC and MCC capture: each secondary diagnosis must be documented as present, monitored, evaluated or treated during the stay to survive a DRG-validation review. 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 599 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.

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Frequently asked questions — DRG 599

What is MS-DRG 599?

MS-DRG 599 is "Malignant Breast Disorders without CC/MCC", a medical Medicare Severity Diagnosis-Related Group in MDC 09, Diseases and Disorders of the Skin, Subcutaneous Tissue and Breast. 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 599?

The FY2027 relative weight is 0.6930 (IPPS final rule Table 5, effective October 1, 2026). In FY2026 it was 0.7690, a change of -9.9%.

What is the average length of stay for DRG 599?

CMS reports a geometric mean length of stay of 1.8 days and an arithmetic mean of 2.2 days for FY2027. The geometric mean is used for transfer-payment calculations.

Which DRGs are in the same CC/MCC family as 599?

DRG 597 (Malignant Breast Disorders with MCC, weight 1.7380); DRG 598 (Malignant Breast Disorders with CC, weight 1.0960). The family's weights range from 0.6930 to 1.7380, so documented complications and comorbidities change payment materially.

What documentation supports the severity level of DRG 599?

DRG 599 is the base-severity assignment: no secondary diagnosis on the CC or MCC lists was coded, or the only ones present are excluded for this principal diagnosis. Revenue-integrity review here looks for undercapture, meaning conditions treated during the stay (electrolyte disorders, specified anemia, acute blood loss, pressure injuries present on admission) that were never documented to the specificity the lists require. A compliant query to the attending, not a coder assumption, is the only way to move a stay to the CC or MCC sibling.

Which codes group to DRG 599?

The v44 Definitions Manual lists 74 principal diagnosis codes for this group. Examples from the principal diagnosis list: C50011 (Malignant neoplasm of nipple and areola, right female breast); C50012 (Malignant neoplasm of nipple and areola, left female breast); C50019 (Malignant neoplasm of nipple and areola, unspecified female breast); C50021 (Malignant neoplasm of nipple and areola, right male breast).

Is DRG 599 a post-acute transfer DRG?

No. DRG 599 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.

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.