Acute Postinfectious Glomerulonephritis

Acute postinfectious glomerulonephritis is an immune-mediated inflammatory injury to the glomeruli that produces a nephritic syndrome. The best-known form is post-streptococcal glomerulonephritis (PSGN), which follows infection with nephritogenic strains of group A Streptococcus (GAS). The organism is not directly invading the kidney; the renal injury results from the immune response that follows the infection. After GAS pharyngitis, PSGN usually appears after a latent period of about 10 days. After impetigo or another GAS skin infection, the interval may extend to approximately 3 weeks. A patient with new facial oedema, dark or visibly bloody urine, reduced urine output, and hypertension during this interval has a classic nephritic presentation. Inflamed glomerular capillaries filter less effectively. Sodium and water are retained, producing oedema and hypertension, while damaged filtration barriers allow red blood cells and protein to enter the urine. The immediate clinical threat is therefore not the old sore throat itself; it is fluid overload, impaired kidney function, hyperkalaemia, or severe hypertension.