Diagnosing Lupus Nephritis

Initial Diagnostic Approach

The American College of Rheumatology (ACR) criteria for lupus nephritis include persistent proteinuria >0.5g/day or >3+ by dipstick, and/or cellular casts, which should prompt suspicion of lupus nephritis in SLE patients 1, 2
A spot urine protein/creatinine ratio >0.5 can be used as a substitute for the 24-hour protein measurement, according to the ACR 1
Active urinary sediment (>5 RBC/hpf, >5 WBC/hpf without infection, or RBC/WBC casts) can substitute for cellular casts in the diagnosis of lupus nephritis 1

Renal Biopsy: The Definitive Test

The International Society of Nephrology/Renal Pathology Society (ISN/RPS) recommends that all patients with clinical evidence of active lupus nephritis should undergo renal biopsy unless strongly contraindicated 1, 3
Renal biopsy allows classification of lupus nephritis according to the ISN/RPS criteria, which guides treatment decisions, as recommended by the American College of Rheumatology 1, 4
Biopsy is particularly recommended in patients with increasing serum creatinine without compelling alternative causes, confirmed proteinuria ≥1.0 g/24 hours, or proteinuria ≥0.5 g/24 hours plus hematuria or cellular casts, according to the ACR 1

Biopsy Processing and Evaluation

Renal tissue should be processed for light microscopy (LM), immunofluorescence (IF), and electron microscopy (EM), as recommended by the International Society of Nephrology/Renal Pathology Society 4
A minimum of 10 glomeruli is generally appropriate for evaluation, according to the ISN/RPS 4
Biopsy allows classification into six classes (I-VI) according to ISN/RPS criteria, which is essential for guiding treatment decisions, as recommended by the American College of Rheumatology 1, 4

Classification and Scoring Systems

The ISN/RPS classification divides lupus nephritis into classes I-VI based on glomerular involvement, which is a crucial step in guiding treatment decisions, as recommended by the American College of Rheumatology 1, 4

Clinical Implications of Biopsy Findings

Class I (minimal mesangial) and Class II (mesangial hypercellularity) generally do not require immunosuppressive treatment, according to the American College of Rheumatology 1
Class III (focal proliferative, <50% of glomeruli) and Class IV (diffuse proliferative, ≥50% of glomeruli) require aggressive therapy with glucocorticoids and immunosuppressive agents, as recommended by the ACR 1
Class V (membranous) when combined with III or IV should be treated like III or IV; pure membranous may be approached differently, according to the American College of Rheumatology 1
Class VI (advanced sclerosis in ≥90% of glomeruli) generally requires preparation for renal replacement therapy rather than immunosuppression, as recommended by the ACR 1

Diagnosing Lupus Nephritis

Introduction to Lupus Nephritis Diagnosis

Lupus nephritis cannot be definitively ruled out without a renal biopsy, as clinical and serological tests cannot accurately predict histological findings, according to the European League Against Rheumatism 5, 6

Clinical Screening Approach

The American College of Rheumatology recommends monitoring for specific urinary abnormalities, including proteinuria ≥0.5 g/24 hours, which is the primary screening threshold, with a strength of evidence level of high 5, 6
Glomerular hematuria with cellular casts significantly increases suspicion of lupus nephritis, with a moderate level of evidence 5, 6

Renal Biopsy Indications

The European League Against Rheumatism suggests that a renal biopsy should be performed when there is proteinuria ≥0.5 g/24 hours with glomerular hematuria, or GFR <30 ml/min with normal kidney size and evidence of active disease, with a high level of evidence 5, 6
The timing of the biopsy is critical, and it should be performed within the first month after disease onset, preferably before immunosuppressive treatment, with a moderate level of evidence 5, 6

Adequate Biopsy Requirements

The International Society of Nephrology recommends that a proper evaluation of the biopsy must include a minimum of 10 glomeruli for light microscopy, with a high level of evidence 7, 8, 6
The biopsy must also include light microscopy with H&E, PAS, Masson's trichrome, and silver stain, as well as immunofluorescence for IgG, C3, IgA, IgM, C1q, κ and λ light chains, with a moderate level of evidence 6

Common Pitfalls to Avoid

The American College of Rheumatology advises against relying solely on clinical parameters, as the threshold for biopsy should be low because clinical, serological, or laboratory tests cannot accurately predict histological findings, with a high level of evidence 5, 6
The European League Against Rheumatism recommends against delaying biopsy for advanced GFR decline, even with GFR <30 ml/min, if kidney size is normal and there is evidence of active disease, with a moderate level of evidence 5, 6

Lupus Nephritis Classification and Management

Classification and Diagnostic Criteria

The International Society of Nephrology/Renal Pathology Society (ISN/RPS) classifies lupus nephritis into six distinct classes, with Class II defined by mesangial immune deposits with mesangial hypercellularity (four or more nuclei fully surrounded by matrix in the mesangial area) 9
The 2018 ISN/RPS revision recommends subdivisions for active and sclerotic lesions rather than the previous A/C designations for Class III, and proposes modified NIH activity and chronicity scoring indices to replace the previous A, C, and A/C designations for Classes III and IV 10, 11
A minimum of 10 glomeruli is required for adequate evaluation, with renal tissue processed for light microscopy, immunofluorescence, and electron microscopy 9, 10

Pathologic Features and Treatment

Class IV lupus nephritis involves ≥50% of total glomeruli with active or inactive diffuse, segmental, or global endocapillary or extracapillary glomerulonephritis, requiring aggressive immunosuppression with glucocorticoids and cytotoxic agents, with the term "endocapillary proliferation" replaced by "endocapillary hypercellularity" to reflect that most hypercellularity is due to inflammatory cell influx rather than actual cell proliferation 9, 10, 11, 12
Lupus vasculopathy is defined as luminal narrowing of arterioles or terminal interlobular arteries by intramural immune deposits, typically with fibrinoid changes, without vessel wall inflammation, and interstitial inflammation should be reported as occurring with or without interstitial fibrosis 10, 11

Renal Biopsy Indications and Clinical Implications in Lupus Nephritis

Definition & Epidemiology

Lupus nephritis is an immune‑complex mediated glomerulonephritis that occurs in patients with systemic lupus erythematosus and is characterized by proteinuria, active urinary sediment, and/or a progressive decline in kidney function. American College of Rheumatology. 13, 14
The lifetime incidence of lupus nephritis among individuals with SLE ranges from 20 % to 60 %, with higher rates observed in Asian, African/Caribbean, and Hispanic populations. American College of Rheumatology. 14
Childhood‑onset SLE confers a particularly high risk for developing severe lupus nephritis. American College of Rheumatology. 14

Indications for Renal Biopsy

Absolute Indications

All patients with clinical evidence of active lupus nephritis who have not previously received immunosuppressive therapy should undergo a renal biopsy unless a strong contraindication exists. American College of Rheumatology. 13, 15, 16

Specific Clinical Scenarios

An unexplained decrease in glomerular filtration rate (GFR) without an alternative explanation warrants biopsy to clarify renal pathology. American College of Rheumatology. 14

Why Biopsy Is Indispensable

Clinical, serological, and routine laboratory parameters cannot reliably predict renal histology; therefore, biopsy remains the only definitive diagnostic tool for lupus nephritis. American College of Rheumatology. 15, 16
Biopsy provides essential information for:
- Classification – determination of ISN/RPS class (I–VI), which directly guides treatment intensity. American College of Rheumatology. 13
- Activity vs. Chronicity Assessment – differentiation of reversible inflammatory lesions from irreversible fibrosis, informing decisions about immunosuppression. American College of Rheumatology. 13
- Prognostication – activity and chronicity indices derived from the specimen predict therapeutic response and long‑term renal outcomes. American College of Rheumatology. 13

Technical Requirements for an Adequate Biopsy

A minimum of 10 glomeruli must be obtained to allow reliable light‑microscopy evaluation. Kidney International. 17
Light‑microscopy sections should be stained with hematoxylin & eosin, periodic acid‑Schiff, Masson's trichrome, and silver stains to assess structural changes. American College of Rheumatology. 13

Timing Considerations – When Not to Delay Biopsy

Even in patients with advanced kidney dysfunction (e.g., GFR < 30 mL/min), a biopsy should be performed if kidney size is preserved and there is evidence of active disease, because chronic kidney disease alone does not preclude the detection of superimposed active lesions. American College of Rheumatology. 14

Treatment Implications Based on Biopsy Classification

Class III (focal proliferative) and Class IV (diffuse proliferative) lupus nephritis require aggressive immunosuppression with glucocorticoids combined with either mycophenolate mofetil or cyclophosphamide. American College of Rheumatology. 13, 15
Class V (membranous) disease:
- When co‑existing with Class III/IV lesions, it is managed as a proliferative disease (same regimen as above).
- Pure Class V presenting with nephrotic‑range proteinuria also warrants immunosuppressive therapy. American College of Rheumatology. 13, 15
Class VI (≥ 90 % glomerular sclerosis) indicates end‑stage pathology; the focus shifts to preparation for renal replacement therapy rather than immunosuppression. American College of Rheumatology. 13