Should I Order This Test?

Could This Be Lupus (SLE)?

Estimate the pre-test probability of systemic lupus erythematosus and determine whether ANA and reflex testing are appropriate. Based on the weighted 2019 EULAR/ACR classification framework.

📋 Adapted from 2019 EULAR/ACR SLE Classification Criteria · Sensitivity 96% · Specificity 93%
ANA ≥1:80 is required as an entry criterion for formal SLE classification. Use this tool to determine whether the clinical picture justifies ordering an ANA — and whether the probability of SLE warrants further workup if it returns positive.
Evidence Base
The scoring system used in this calculator is adapted from the 2019 EULAR/ACR classification criteria for SLE, which demonstrate high diagnostic performance in validation cohorts. A negative ANA (<1:80 by IIF on HEp-2 cells) makes SLE very unlikely.
~96%
Sensitivity
~93%
Specificity
97–99%
ANA sensitivity for SLE
1
Constitutional
Select if present and unexplained by another diagnosis.
Fever >38°C
Unexplained, not due to infection or other cause
+2
2
Mucocutaneous
Select all present on history or examination.
Malar (butterfly) rash
Fixed erythema over cheeks and nasal bridge, spares nasolabial folds
+6
Photosensitive rash
Rash in sun-exposed areas — reported by patient or observed by clinician
+3
Oral or nasal ulcers
Usually painless oral ulcers — more specific than painful apthous ulcers
+2
Non-scarring alopecia
Diffuse hair thinning or fragility — not alopecia areata or androgenic
+2
Discoid lupus rash
Scarring, erythematous plaques with follicular plugging
+4
3
Musculoskeletal
Joint involvement in SLE is typically non-erosive and symmetric.
Symmetric inflammatory arthritis
≥2 joints with synovitis (swelling, warmth) — or joint pain with ≥30 min morning stiffness
+6

SLE arthritis is typically non-erosive and involves small joints of the hands and wrists. Unlike RA, joint damage on X-ray is uncommon even with active disease.

4
Serosal
Unexplained serositis — after excluding infection and malignancy.
Pleuritis
Pleuritic chest pain, pleural rub, or pleural effusion
+5
Pericarditis
Pericardial pain, rub, effusion on echo, or EKG changes
+6
5
Renal
Lupus nephritis is a major cause of morbidity — carry a high index of suspicion with urinary findings.
Proteinuria ≥500 mg/24h or protein:creatinine ≥0.5
New or unexplained — evaluate with spot urine protein:creatinine ratio
+4
Active urinary sediment
RBC casts, WBC casts, or dysmorphic RBCs on microscopy
+4

Renal involvement is a red flag. Lupus nephritis can be clinically silent early. A urinalysis with microscopy should be part of any SLE workup when renal involvement is suspected.

6
Hematologic
Unexplained cytopenias — after excluding other causes.
Leukopenia <4,000/mm³
On at least one occasion — not medication-related
+3
Thrombocytopenia <100,000/mm³
Not due to medications, TTP, or other causes
+4
Hemolytic anemia
Positive Coombs test, elevated LDH, low haptoglobin
+4
7
Immunologic Labs (if already available)
Include if labs have already been ordered. Leave unchecked if not yet obtained.
Anti-dsDNA positive
High specificity (~95%) for SLE. Titers correlate with disease activity.
+6
Anti-Sm positive
Highly specific for SLE (~99%) — low sensitivity (~30%)
+6
Low complement (C3 and/or C4)
Consumption suggests active immune complex disease — especially lupus nephritis
+4
Antiphospholipid antibodies positive
Lupus anticoagulant, anti-cardiolipin, or anti-β2GPI
+2
i
SLE Classification Criteria — Performance Comparison
The 2019 EULAR/ACR criteria outperform prior versions in sensitivity while maintaining specificity.
Criteria Sensitivity Specificity
EULAR/ACR 2019 ← used here 96.1% 93.4%
SLICC 2012 96.7% 83.7%
ACR 1997 82.8% 93.4%
Suspicion Score
0
pts
<5 Very Low 5–9 Consider ≥10 High
Score Breakdown
Constitutional—
Mucocutaneous—
Musculoskeletal—
Serosal—
Renal—
Hematologic—
Immunologic labs—
Recommendation
🔵
Select clinical features to estimate SLE probability.
🟢 Very Low Probability
SLE is unlikely
Clinical features do not suggest a systemic autoimmune disease. ANA testing is generally not indicated at this stage. Reassess if new objective signs develop.
🟡 Consider Testing
SLE cannot be excluded
Multiple features raise suspicion. Order ANA to screen. If ANA ≥1:80, proceed to reflex testing below. A negative ANA makes SLE very unlikely (sensitivity 97–99%).
ANA method matters: Order IIF on HEp-2 cells — superior sensitivity vs ELISA or multiplex assays.
Initial Labs
ANA (IIF) CBC CMP UA + microscopy ESR / CRP
🔴 High Suspicion
SLE workup indicated
Rheumatology referral recommended. Order full SLE panel now — do not wait for ANA result before initiating broader workup if features are compelling.
Note: ≥10 points + positive ANA meets formal 2019 EULAR/ACR classification threshold for SLE.
Recommended Labs
Rheumatology referral ANA (IIF) Anti-dsDNA Complement C3/C4 UA + microscopy Anti-Sm Anti-SSA/SSB Antiphospholipid Ab CBC CMP
Scoring Reference
Malar rash+6
Symmetric arthritis+6
Pericarditis+6
Anti-dsDNA+6
Anti-Sm+6
Pleuritis+5
Discoid rash+4
Proteinuria+4
Active urinary sediment+4
Thrombocytopenia+4
Hemolytic anemia+4
Low complement+4
Photosensitivity+3
Leukopenia+3
Oral/nasal ulcers+2
Non-scarring alopecia+2
Fever >38°C+2
Antiphospholipid Ab+2
<5 Very Low  ·  5–9 Consider ANA  ·  ≥10 High suspicion

Frequently Asked Questions

Common questions clinicians and patients ask after using this tool — and after receiving these results.

What are the first signs of lupus? ▼
Lupus (SLE) most commonly presents with fatigue, joint pain, and skin rashes — particularly the malar (butterfly) rash across the cheeks and nose that worsens with sun exposure. Many patients first notice that their symptoms flare after UV exposure. Other early features include oral ulcers, hair loss, and low-grade fevers. Because lupus can affect almost any organ system, early presentations are highly variable — the diagnosis is often delayed by years. The combination of joint symptoms, photosensitive rash, and unexplained cytopenias in a young woman should always prompt lupus evaluation.
Who is most likely to develop lupus? ▼
Lupus predominantly affects women of childbearing age (female:male ratio of approximately 9:1), with peak onset between ages 15–44. It is significantly more common and often more severe in women of African, Asian, and Hispanic descent compared to women of European descent. Having a first-degree relative with lupus increases risk approximately 20-fold. Certain HLA haplotypes (DR2, DR3) are associated with increased susceptibility. Men can develop lupus and often have more severe disease with higher rates of renal and neurologic involvement.
What blood tests are used to diagnose lupus? ▼
The core lupus antibody panel includes: ANA (positive in >95% of SLE — a negative ANA makes lupus unlikely), anti-dsDNA (highly specific for SLE, ~70% sensitive; useful for monitoring disease activity), anti-Sm (highly specific, ~30% sensitive), and complement C3/C4 (low complement indicates active disease consuming complement via immune complexes). Additional tests: CBC (cytopenias), urinalysis (proteinuria/hematuria suggesting nephritis), CRP/ESR, and a direct Coombs test if hemolytic anemia is suspected. Anti-dsDNA and complement are the most useful for tracking flares.
Can lupus cause kidney disease? ▼
Yes — lupus nephritis is one of the most serious manifestations of SLE, occurring in approximately 40–60% of lupus patients over the course of their disease. It presents with proteinuria, hematuria, RBC casts on urine microscopy, and rising creatinine. Lupus nephritis can be clinically silent in early stages, which is why urinalysis and renal function monitoring is recommended routinely in SLE patients. Untreated lupus nephritis can lead to end-stage renal disease. A new onset of hematuria or proteinuria in a lupus patient should be evaluated urgently.
Is lupus curable? ▼
Lupus is not curable but is highly treatable, and most patients with proper treatment can lead normal or near-normal lives. Treatment has improved dramatically over the past two decades. Hydroxychloroquine (Plaquenil) is prescribed to virtually all lupus patients and reduces flares, organ damage, and mortality. Steroids manage acute flares, and immunosuppressants (mycophenolate, azathioprine, belimumab) are used for organ-threatening disease. The goal is remission — defined as minimal disease activity on stable therapy. Regular rheumatology follow-up is essential.
What is drug-induced lupus, and which drugs cause it? ▼
Drug-induced lupus (DIL) is a lupus-like syndrome triggered by certain medications. It typically resolves within weeks to months of stopping the causative drug. Common culprits include: hydralazine, procainamide, isoniazid, minocycline, TNF inhibitors (like infliximab), and methyldopa. DIL typically causes arthralgias, serositis, and a positive ANA — but unlike idiopathic SLE, it rarely causes serious nephritis or CNS involvement, and anti-dsDNA is usually negative. Anti-histone antibody is characteristically positive in drug-induced lupus.
References
  1. Aringer M, Costenbader K, Daikh D, et al. 2019 European League Against Rheumatism/American College of Rheumatology classification criteria for systemic lupus erythematosus. Ann Rheum Dis. 2019;78(9):1151–1159.
  2. Aringer M, et al. Development and validation of the 2019 EULAR/ACR SLE classification criteria. Ann Rheum Dis. 2019.
  3. Schmidtmann I, et al. Validation of the 2019 EULAR/ACR classification criteria for systemic lupus erythematosus. RMD Open. 2023.
  4. Petri M, et al. Derivation and validation of the Systemic Lupus International Collaborating Clinics classification criteria for SLE. Arthritis Rheum. 2012;64(8):2677–2686.