Diagnosing Acute Glomerulonephritis: Clinical Criteria and Key Indicators

Acute glomerulonephritis (AGN) is a sudden inflammation of the glomeruli—the tiny filters in the kidneys—often triggered by a preceding infection, most commonly streptococcal. While kidney biopsy remains the definitive method for diagnosis, it's typically not required due to the self-limiting nature of the condition and its favorable clinical course. Instead, healthcare providers rely on a combination of clinical symptoms, laboratory findings, and patient history to make an accurate diagnosis.

Primary Clinical Features of Acute Glomerulonephritis

The hallmark presentation of acute glomerulonephritis usually appears 1 to 2 weeks after a streptococcal infection, such as pharyngitis or skin infection. Patients often develop a classic triad of symptoms: hematuria (blood in urine), proteinuria (excess protein in urine), and signs of fluid retention like facial or peripheral edema. Many also experience elevated blood pressure, which can range from mild to severe.

Visible hematuria may give the urine a cola- or tea-colored appearance, while microscopic hematuria is detected through urinalysis. Proteinuria is generally mild to moderate, distinguishing AGN from nephrotic syndrome, where protein loss is significantly higher.

Laboratory Markers Supporting Diagnosis

Elevated Anti-Streptolysin O (ASO) Titers

Blood tests often reveal increased levels of anti-streptolysin O (ASO), indicating a recent group A streptococcal infection. This serological marker helps establish the link between the antecedent infection and the onset of kidney inflammation.

Complement C3 Levels: A Key Diagnostic Clue

Another critical lab finding is a decrease in serum complement C3 levels. In post-infectious glomerulonephritis, C3 is typically low during the acute phase but shows spontaneous recovery within 6 to 8 weeks. This pattern differentiates it from other forms of glomerulonephritis, such as lupus nephritis or membranoproliferative glomerulonephritis, where complement levels may remain suppressed longer or involve both C3 and C4.

When Is a Kidney Biopsy Necessary?

Although most cases of acute glomerulonephritis are diagnosed clinically, a renal biopsy may be warranted in atypical presentations—such as rapidly declining kidney function, persistent heavy proteinuria, or absence of a clear infectious trigger. Histopathology would reveal endocapillary proliferative glomerulonephritis, characterized by increased cellularity within the glomerular capillaries.

Management and Prognosis

Treatment for acute glomerulonephritis is primarily supportive and symptom-based. This includes controlling hypertension with antihypertensive medications, managing fluid overload with diuretics, and monitoring kidney function closely. Dietary modifications, such as reduced salt intake, are also recommended.

While the majority of patients recover fully without long-term complications, a small subset may develop serious issues such as hypertensive encephalopathy, acute heart failure, or acute kidney injury requiring temporary dialysis. Prompt recognition and management of these complications are crucial for improving outcomes.

Overall, the prognosis for acute glomerulonephritis is excellent, especially in children. Most individuals experience complete resolution of symptoms and normalization of lab values within several weeks to months. Regular follow-up ensures timely detection of any lingering abnormalities and supports full recovery.