Nephritic Syndrome and RPGN

The nephritic syndrome is the clinical expression of inflammatory glomerular injury: glomerular haematuria (often with dysmorphic red cells and red-cell casts), variable proteinuria, hypertension, and a fall in glomerular filtration with fluid retention. When such injury is severe and crescents form across many glomeruli, kidney function can deteriorate over days to weeks — the pattern termed rapidly progressive glomerulonephritis (RPGN), one of the few nephrologic states regarded as urgent.

Definition

Nephritic syndrome is a constellation of glomerular haematuria, variable proteinuria, hypertension, and reduced glomerular filtration arising from inflammatory glomerular injury; rapidly progressive glomerulonephritis is the subset in which extensive crescent formation produces loss of kidney function over days to weeks.

Scope

This entry defines the nephritic pattern, contrasts it with the nephrotic pattern, and describes the crescentic, rapidly progressive end of the spectrum and its immunopathologic categories (immune-complex, pauci-immune, and anti-GBM). It is a reference description of how the syndrome is recognised and classified, not a protocol for diagnosis or treatment, which rest with current guidelines and clinicians.

Core questions

• Is the urinary picture genuinely glomerular (dysmorphic haematuria, red-cell casts) rather than from the lower tract?
• Is kidney function stable or falling rapidly enough to suggest a crescentic, rapidly progressive process?
• Which immunopathologic category — immune-complex, pauci-immune, or anti-GBM — does the serology and biopsy suggest?
• Is the process confined to the kidney or part of a systemic vasculitis or autoimmune disease?

Key concepts

• Glomerular (dysmorphic) haematuria and red-cell casts
• Crescent formation
• Three immunopathologic categories: immune-complex, pauci-immune, anti-GBM
• Rapidly progressive glomerulonephritis (RPGN)
• Nephritic-nephrotic overlap
• Complement consumption in some immune-complex forms

Mechanisms

Inflammatory injury to the glomerular capillary wall increases its permeability to red cells and protein and recruits inflammatory cells, producing haematuria, proteinuria, and reduced filtration. When injury ruptures the capillary wall and Bowman's capsule, fibrin and proliferating parietal epithelial and inflammatory cells accumulate in Bowman's space to form crescents — the histologic hallmark of rapidly progressive disease. Crescentic glomerulonephritis is conventionally divided into three immunopathologic categories by immunofluorescence: immune-complex (granular deposits, e.g. lupus, IgA, post-infectious), pauci-immune (little or no staining, typically ANCA-associated), and anti-glomerular basement membrane disease (linear staining). The category, rather than the crescents alone, frames the systemic associations and serologic evaluation (Jennette 2012; Benzing 2021; Floege 2018).

Clinical relevance

Recognising a nephritic pattern, and especially a rapidly progressive course, is a central organising step in evaluating glomerular disease because it narrows the differential and signals which systemic associations and serologic tests are typically considered. This entry describes that conceptual framework; it does not provide diagnostic thresholds, urgency criteria, or treatment for individual patients, which are addressed by current guidelines and treating clinicians.

Epidemiology

Nephritic presentations span common entities such as IgA nephropathy and post-infectious glomerulonephritis and less common but consequential crescentic diseases. Rapidly progressive glomerulonephritis is uncommon overall, but among its causes ANCA-associated disease predominates in older adults, while anti-GBM disease is rarer; the distribution varies with age and region (Jennette 2012; Rovin 2021).

History

The clinical concept of acute nephritis is old, but its modern subdivision rests on twentieth-century immunofluorescence, which separated immune-complex, pauci-immune, and anti-GBM patterns and reframed RPGN as an immunopathologic rather than purely morphologic diagnosis. The Chapel Hill Consensus nomenclature and successive KDIGO guidelines later standardised the terminology and categories used today (Jennette 2012; Rovin 2021).

Key figures

• J. Charles Jennette
• Ronald J. Falk
• David J. Salant

Seminal works

• jennette2012
• benzing2021
• rovin2021

Frequently asked questions

What makes haematuria 'glomerular'?

Glomerular bleeding typically produces dysmorphic (misshapen) red cells and red-cell casts in the urine, reflecting passage through an inflamed filtration barrier, which distinguishes it from bleeding originating in the lower urinary tract.

Why is rapidly progressive glomerulonephritis considered urgent?

Because extensive crescent formation can destroy functioning glomeruli over days to weeks, the window in which the underlying immune process is conventionally evaluated and addressed is short; this entry describes the concept rather than offering management guidance.