BILAG-2004: System-based assessment of lupus disease activity across 9 organ systems.
Constitutional System
Grade Each System
Select each organ system and assign a grade (A-E) to generate the BILAG summary.
Guidelines & Evidence
Verified
Last Review: 2026-07-17
When to Use
When to Use
Comprehensive assessment of lupus disease activity across 9 organ systems
Detecting partial flares and organ-specific activity not captured by global scores
Clinical trial endpoint requiring granular organ-system evaluation
Guiding organ-specific treatment decisions in SLE
Longitudinal monitoring of disease activity patterns
Patient Population
Adults and children with confirmed SLE (ACR 1997 or SLICC 2012 criteria). The BILAG-2004 is validated for use in clinical trials and observational cohorts. It is more sensitive to partial improvement than SLEDAI because each organ system is graded independently.
Contraindications
Requires trained assessor familiar with BILAG glossary definitions
Time-intensive compared to SLEDAI; less practical for rapid clinic assessments
Not designed for non-lupus systemic autoimmune diseases
How it Works
Grading System
| Grade | Meaning | Clinical Implication |
|---|---|---|
| A | Severe disease activity | Requires high-dose steroids, immunosuppressants, or biologics |
| B | Moderate disease activity | Requires low-dose steroids, antimalarials, or symptomatic therapy |
| C | Mild disease activity | Stable; no change in therapy typically needed |
| D | Inactive, previously involved | Surveillance only |
| E | Never involved | No current or past activity in this system |
Organ Systems Assessed
General (constitutional) — fever, weight loss, lymphadenopathy, fatigue
Mucocutaneous — rash, alopecia, mucosal ulcers, panniculitis
Neuropsychiatric — seizure, psychosis, mononeuritis, myelopathy, headache
Musculoskeletal — arthritis, myositis, tendonitis
Cardiorespiratory — pleurisy, pericarditis, pneumonitis, myocardial involvement
Renal — proteinuria, casts, haematuria, hypertension, declining GFR
Haematological — haemolytic anaemia, thrombocytopenia, leukopenia
Ophthalmic — retinal vasculitis, episcleritis, scleritis
Gastrointestinal — peritonitis, serositis, vasculitic mesenteric ischaemia
Scoring Method
Each of the 9 organ systems receives a letter grade (A–E) based on the presence and severity of clinical features. The grade is determined by a rules-based system: an A grade requires at least one severe manifestation; a B grade requires moderate manifestations; C is for mild features or resolved A/B activity; D is for past involvement now inactive; E is never involved. A global score can be calculated by converting A = 9, B = 3, C = 1, D = 0, E = 0 and summing across systems.
Clinical Pearls
Clinical Application
The BILAG-2004 is more discriminating than SLEDAI-2K for detecting partial treatment responses, because a patient may transition from an A to a B without changing their global SLEDAI score. Its organ-system granularity makes it ideal for lupus trials where demonstrating differential organ response is important. In clinical practice, the BILAG is particularly useful when managing patients with complex multisystem lupus, as the letter-grade system directly maps to treatment intensity for each organ.
Pitfalls to Avoid
Do not assign A and B grades to the same system simultaneously; A takes precedence
Attribution to lupus is critical — exclude infection, drug effects, and comorbidities
BILAG-2004 requires formal training for reliable use in clinical trials
The conversion to numeric global score loses organ-specific information
Chronic damage can be difficult to distinguish from activity, especially in renal and CNS systems
Next Steps
Action by Grade
| Grade | Typical Response |
|---|---|
| Any A | Escalate immunosuppression; consider high-dose corticosteroids, IV cyclophosphamide, or biologic therapy |
| 1 B (no A) | Consider increasing or adding immunosuppressive agent; low-to-moderate steroids |
| 2+ B (no A) | Multiple systems moderately active; may require treatment intensification similar to an A |
| C or D only | Maintain current therapy; monitor for deterioration |
| All E | No lupus activity; continue surveillance as appropriate |
When to Reassess
Every 1–3 months during active disease (any A or multiple B grades)
Every 3–6 months in stable disease (C, D, or single B)
Immediately on clinical suspicion of flare
At each dose change of major immunosuppressive therapy
The Evidence
Key Evidence
BILAG-2004 demonstrated excellent inter-rater reliability and construct validity in international validation studies
Used as the primary efficacy endpoint in multiple phase 2 and 3 SLE trials including tabalumab and anifrolumab
A to B transitions correlate with reduction in steroid dose and physician global assessment
BILAG-2004 shows superior sensitivity to change compared to SLEDAI-2K in clinical trials
Primary Reference
BILAG 2004. Development and initial validation of an updated version of the British Isles Lupus Assessment Group's disease activity index for patients with systemic lupus erythematosus.
Isenberg DA et al. • Rheumatology. 2005;44(7):902-6
Revised British Isles Lupus Assessment Group 2004 index: a reliable tool for assessment of systemic lupus erythematosus activity.
Yee CS et al. • Arthritis and Rheumatism. 2006;54(10):3300-5
Origins & History
Development
The BILAG index originated in the 1980s from the British Isles Lupus Assessment Group, a consortium of UK rheumatologists. The original BILAG was published in 1988 and underwent major revision to become the BILAG-2004. The 2004 revision simplified the scoring rules, expanded neuropsychiatric items, and improved the glossary definitions to enhance reliability across centres. The index follows a transitional approach, meaning it scores change in activity compared to the previous assessment.
Last Comprehensive Review: 2026-07-17