HL7 DG1 Segment: Diagnosis
The HL7 DG1 segment (Diagnosis) carries diagnosis codes associated with a patient encounter. It repeats for multiple diagnoses and appears in ADT, ORM, and DFT messages. DG1 is critical for billing, clinical decision support, quality reporting, and public health surveillance.
DG1 Field Reference
Section titled “DG1 Field Reference”| Seq | Name | Type | Opt | Description |
|---|---|---|---|---|
DG1-1 | Set ID | SI | R | Sequence number (1, 2, 3...) |
DG1-2 | Diagnosis Coding Method | ID | O | Coding system version indicator |
★ DG1-3 | Diagnosis Code | CE | O | ICD-10-CM code and description |
| CE data type: code^description^coding system (e.g., R50.9^Fever, unspecified^I10). I10=ICD-10-CM, I9=ICD-9-CM (legacy), SCT=SNOMED CT. | ||||
DG1-4 | Diagnosis Description | ST | O | Text description (if DG1-3 is empty) |
★ DG1-5 | Diagnosis Date/Time | TS | O | When the diagnosis was established |
★ DG1-6 | Diagnosis Type | IS | R | A (Admitting), W (Working), F (Final) |
| A=Admitting (at admission), W=Working (evolves during encounter), F=Final (at discharge). The final diagnosis in ADT^A03 is billing-critical. | ||||
DG1-7 | Major Diagnostic Category | CE | O | MDC for DRG grouping |
DG1-8 | Diagnostic Related Group | CE | O | DRG code |
DG1-9 | DRG Approval Indicator | ID | O | Y/N — DRG approved |
DG1-10 | DRG Grouper Review Code | IS | O | Grouper review outcome |
DG1-11 | Outlier Type | CE | O | Day outlier, cost outlier |
DG1-12 | Outlier Days | NM | O | Number of outlier days |
DG1-13 | Outlier Cost | CP | O | Outlier cost amount |
DG1-14 | Grouper Version and Type | ST | O | DRG grouper software version |
★ DG1-15 | Diagnosis Priority | ID | O | 1 = Primary, 2+ = Secondary |
| 1=Primary/Principal (drives DRG and reimbursement), 2=Secondary (comorbidity, may increase DRG weight), 3+=Additional documentation. | ||||
★ DG1-16 | Diagnosing Clinician | XCN | O | Physician who made the diagnosis |
DG1-17 | Diagnosis Classification | IS | O | Classification category |
DG1-18 | Confidential Indicator | ID | O | Y if diagnosis is confidential |
DG1-19 | Attestation Date/Time | TS | O | When diagnosis was attested |
DG1-20 | Diagnosis Identifier | EI | O | Unique diagnosis instance ID |
DG1-21 | Diagnosis Action Code | ID | O | A (Add), D (Delete), U (Update) |
★ DG1-3 O ICD-10-CM code and description
CE data type: code^description^coding system (e.g., R50.9^Fever, unspecified^I10). I10=ICD-10-CM, I9=ICD-9-CM (legacy), SCT=SNOMED CT.
★ DG1-6 R A (Admitting), W (Working), F (Final)
A=Admitting (at admission), W=Working (evolves during encounter), F=Final (at discharge). The final diagnosis in ADT^A03 is billing-critical.
★ DG1-15 O 1 = Primary, 2+ = Secondary
1=Primary/Principal (drives DRG and reimbursement), 2=Secondary (comorbidity, may increase DRG weight), 3+=Additional documentation.
R = Required, O = Optional, C = Conditional, W = Withdrawn (backward compatibility only)
DG1-3: Diagnosis Code (ICD-10-CM)
Section titled “DG1-3: Diagnosis Code (ICD-10-CM)”DG1-3 uses the CE (Coded Element) data type to carry the diagnosis code:
DG1|1||R50.9^Fever, unspecified^I10||20260301|A| Component | Value | Meaning |
|---|---|---|
| CE.1 | R50.9 | ICD-10-CM code |
| CE.2 | Fever, unspecified | Code description |
| CE.3 | I10 | Coding system (ICD-10) |
Common Coding System Identifiers
Section titled “Common Coding System Identifiers”| ID | System | Description |
|---|---|---|
| I10 | ICD-10-CM | Diagnosis codes (US) — required for billing |
| I10P | ICD-10-PCS | Procedure codes (inpatient only) |
| I9 | ICD-9-CM | Legacy system (pre-October 2015) |
| SCT | SNOMED CT | Clinical terminology (used in some clinical contexts) |
DG1-6: Diagnosis Type
Section titled “DG1-6: Diagnosis Type”| Code | Type | Description |
|---|---|---|
| A | Admitting | Reason for admission — set at time of admission, may not be the final diagnosis |
| W | Working | Current working diagnosis — updated during the encounter as clinical picture evolves |
| F | Final | Final confirmed diagnosis — established at discharge or after workup completion |
Diagnosis Type Lifecycle
Section titled “Diagnosis Type Lifecycle”Admission: DG1 with Type A (Admitting) → "Chest pain, unspecified" (R07.9)During stay: DG1 with Type W (Working) → "Acute myocardial infarction" (I21.9)Discharge: DG1 with Type F (Final) → "STEMI of LAD" (I21.01)ADT^A08 (Update Patient) messages carry updated DG1 segments as the diagnosis evolves. The final diagnosis in the discharge ADT^A03 is the billing-critical diagnosis.
DG1-15: Diagnosis Priority
Section titled “DG1-15: Diagnosis Priority”| Priority | Meaning | Billing Impact |
|---|---|---|
| 1 | Primary/Principal | Drives DRG assignment and primary payer reimbursement |
| 2 | Secondary | Comorbidity/complication — may increase DRG weight |
| 3+ | Additional | Additional documentation, may affect severity of illness |
The primary diagnosis (DG1-15 = 1) must be the condition chiefly responsible for the admission or encounter. Incorrect primary diagnosis assignment leads to DRG miscoding and potential compliance issues.
Key Implementation Considerations
Section titled “Key Implementation Considerations”Multiple DG1 Segments
Section titled “Multiple DG1 Segments”Patients typically have multiple diagnoses. DG1 segments are ordered by clinical significance:
DG1|1||I21.01^STEMI of LAD^I10||20260301|F|||||||||||1DG1|2||I10^Essential hypertension^I10||20260301|F|||||||||||2DG1|3||E11.9^Type 2 DM^I10||20260301|F|||||||||||3DG1|4||Z79.4^Long-term insulin use^I10||20260301|F|||||||||||4DG1-1 (Set ID) indicates segment order; DG1-15 (Priority) indicates clinical/billing priority. These are typically the same but can differ when a system needs to reorder diagnoses without renumbering.
DG1 in DFT vs ADT Context
Section titled “DG1 in DFT vs ADT Context”| Context | Purpose | Timing |
|---|---|---|
| ADT messages | Clinical documentation — reflects evolving clinical picture | Admission through discharge |
| DFT messages | Billing justification — links charges to diagnoses | Post-encounter charge posting |
| ORM messages | Medical necessity — justifies why a test was ordered | At order placement |
In DFT messages, DG1-3 directly impacts claim adjudication. The diagnosis must support medical necessity for the procedure code in FT1. Mismatched diagnosis-procedure pairs are a leading cause of claim denials.
ICD-10 Code Mapping Between Systems
Section titled “ICD-10 Code Mapping Between Systems”When integrating systems that use different coding standards:
- ICD-10-CM ↔ SNOMED CT: GEM (General Equivalence Mappings) provide crosswalks, but mapping is imprecise — clinical review may be required
- ICD-9 → ICD-10: Legacy systems may still send ICD-9 codes. Integration engines should map forward to ICD-10 for downstream billing systems
- Local codes: Some clinical systems use internal shorthand codes that must be mapped to ICD-10 before reaching the billing system
CMS Requirements
Section titled “CMS Requirements”CMS regulations require accurate diagnosis coding for Medicare/Medicaid claims:
- Present on Admission (POA): Inpatient diagnoses must indicate if the condition was present at admission
- Principal diagnosis: Must reflect the condition that, after study, occasioned the admission
- Specificity: Code to the highest level of specificity available (e.g., I21.01 instead of I21.0)