Complement in overt and asymptomatic nephritis after skin infection.

In an ongoing study of streptococcal skin infection and acute glomerulonephritis (AGN) begun in 1964, C'3 determinations were done in 784 patients. There were 126 patients with acute poststreptococcal nephritis, 172 of their siblings, and 486 patients with uncomplicated impetigo from families without an index case of nephritis.90% of the patients with nephritis were infected with one of the four prevalent streptococcal serotypes associated with nephritis in this population; only 12% of patients with uncomplicated impetigo were infected with similar serotypes.93% of the patients with overt nephritis had diminished complement levels. Low complement was more often observed (8%) in AGN siblings than was transient hypertension and/or hematuria (5%). Considering the relationship of low C'3 alone and low C'3 preceded hematuria in four others. Two (0.4%) of the patients with uncomplicated impetigo had low complement values, both of whom were infected with nephritogenic strains. Transient hematuria and/or hypertension was less frequently observed (2.7%) among patients with uncomplicated impetigo. Serial determinations in patients with low complement revealed a return to normal in a linear fashion within 2-12 wk. The validity of the hypothesis that the asymptomatic patients with low complement levels, with or without hematuria, likely had subclinical nephritis is strengthened by the accompanying epidemiologic data. The finding of low complement before the onset of, or in the absence of, hematuria or other evidence of nephritis supports the concept that an immunologic mechanism may precipitate the renal injury of acute streptococcal nephritis.