Acute nephritis (acute nephritic syndrome)

Overview

Acute nephritic syndrome is a pattern of sudden glomerular inflammation that allows blood and protein to leak into urine and reduces the kidneys’ ability to excrete salt, water and metabolic waste. “Acute nephritis” is an imprecise historical term, so a modern evaluation tries to identify the specific glomerular disease rather than treating the label as a final diagnosis. ^{[1] [2]}

Inflammation damages the glomerular filtration barrier. Red blood cells enter the urine, filtration rate falls, and retained sodium and water contribute to edema and hypertension. Immune complexes, autoantibodies, infections and systemic inflammatory disorders can all produce this pattern. ^{[1] [2]}

Post-streptococcal glomerulonephritis often appears after a latent period following strep throat or impetigo, especially in children. Other causes include IgA nephropathy, lupus nephritis, anti-GBM disease and ANCA-associated vasculitis; these require different treatment and can progress rapidly if not recognized. ^{[1] [2] [3]}

Symptoms and warning signs

Common features include dark reddish-brown or cola-colored urine, reduced urine output, puffiness around the eyes, swelling of the legs, fatigue and high blood pressure. Headache, nausea or shortness of breath can occur when hypertension or fluid overload is significant. ^{[1] [2]}

Seek urgent care for very low urine output, severe shortness of breath, chest symptoms, confusion, seizures, rapidly increasing swelling or very high blood pressure. These can signal acute kidney injury, pulmonary edema or hypertensive emergency. ^{[1] [2]}

Diagnosis

Urinalysis is central. Dysmorphic red cells and red-cell casts support glomerular bleeding; protein is commonly present but is usually less prominent than in classic nephrotic syndrome. Blood tests measure creatinine, electrolytes, albumin and blood counts, while complement levels and disease-specific serology help narrow the cause. ^{[1] [2]}

When PSGN is suspected, evidence of a preceding group A strep infection may come from throat or skin cultures and streptococcal antibody testing; complement C3 is commonly low. Depending on the clinical picture, clinicians may test ANA, anti-dsDNA, ANCA, anti-GBM antibodies, hepatitis serology and other markers. Kidney biopsy is considered when the diagnosis is uncertain, disease is severe or the course is atypical. ^{[1] [2] [3]}

Urinary tract bleeding, kidney stones, interstitial nephritis and pigmenturia can also darken urine, but they do not produce the same combination of glomerular sediment, edema and hypertension. Nephrotic syndrome causes heavier protein loss and hypoalbuminemia, although mixed nephritic-nephrotic presentations occur. ^{[2] [3]}

Causes, risk factors and clinical context

Risk depends on the underlying disease. PSGN follows certain group A streptococcal throat or skin infections and is more common in children. Autoimmune disease, systemic vasculitis, chronic infections and certain genetic conditions increase the likelihood of other glomerulonephritides. ^{[1] [2]}

Children with uncomplicated PSGN usually recover kidney function well, although urine abnormalities may take weeks or months to fully normalize. Adults have a higher risk of residual impairment. Rapidly progressive immune causes can permanently damage kidneys unless immunosuppressive or disease-specific therapy begins promptly. ^{[1] [2] [3]}

Complications and why the diagnosis matters

Complications include acute kidney injury, severe hypertension, pulmonary edema, electrolyte disturbance and, in the most severe cases, need for dialysis. Some forms can recur or evolve into chronic kidney disease, depending on the underlying diagnosis. ^{[1] [2]}

Prognosis cannot be predicted from the generic label “acute nephritis.” It depends on the cause, severity at presentation, response to therapy and whether scarring develops. Post-streptococcal disease has an especially favorable prognosis in children. ^{[1] [2] [3]}

Treatment and management

Treatment targets the cause and the physiologic consequences of reduced filtration. Salt and fluid restriction, diuretics for edema and blood-pressure control are common supportive measures. Patients with ongoing group A strep infection receive antibiotics to eradicate the organism and reduce transmission, although antibiotics do not directly reverse the immune kidney injury that has already developed. ^{[1] [2]}

Severe fluid overload, dangerous potassium elevation, metabolic acidosis or uremic complications may require dialysis. Autoimmune causes such as lupus nephritis, ANCA vasculitis or anti-GBM disease can require corticosteroids and other immunosuppressive therapy under specialist care. ^{[1] [2] [3]}

The old advice to treat all “acute nephritis” with a single regimen is unsafe because the syndrome has many causes. Immunosuppression is appropriate for some diagnoses and harmful or unnecessary for others, so cause-specific evaluation is essential. ^{[1] [2]}

Follow-up, recovery and prevention

Follow-up includes blood pressure, kidney function, urine protein and hematuria. Persistent complement abnormalities, proteinuria or impaired renal function beyond the expected recovery period can signal another diagnosis and should prompt nephrology reassessment. ^{[1] [2]}

There is no single preventive strategy for every glomerulonephritis. Good infection control and appropriate treatment of group A strep reduce transmission of the organism, while management of autoimmune and systemic disease reduces risk of recurrent inflammatory kidney injury. ^{[1] [2] [3]}

Special situations and care pathway

Children with PSGN usually do well, whereas adults more often have residual kidney impairment. Pregnancy, pre-existing chronic kidney disease and rapidly progressive forms require particularly close specialist management because both maternal and renal risks are higher. ^{[1] [2] [3]}

A safe pathway is to identify the nephritic pattern, assess blood pressure and fluid status, obtain renal and immune testing, involve nephrology for severe or atypical disease, and reserve biopsy and immunosuppression for cases where they will change management. ^{[1] [2]}

When to seek urgent medical care

Urgent assessment is needed for severe hypertension, breathlessness, rapidly worsening swelling, very low urine output, confusion, seizures, chest symptoms or rapidly rising kidney-function tests. ^{[1] [2]}

Sources

1. CDC — Clinical Guidelines for Post-Streptococcal Glomerulonephritis
2. CDC — About Post-Streptococcal Glomerulonephritis
3. NIDDK — Glomerular Diseases

This article is based on trusted medical sources and is awaiting clinician review. It is not a substitute for personalized medical advice.