Which test result is positive in postinfectious glomerulonephritis, suggesting recent exposure to Group A strep?

In postinfectious glomerulonephritis, particularly following an infection with Group A streptococcus, the anti-streptolysin O (ASO) titer is often used as a diagnostic marker. A positive ASO titer indicates recent exposure to Group A strep, as the body produces antibodies against streptolysin O, a toxin produced by this bacterium. This test is significant because it helps to confirm the linkage between a recent streptococcal infection and the development of glomerulonephritis.

While other tests, such as a throat culture, can indicate an active infection, they may not reflect past infections that have already resolved and lead to glomerulonephritis. Additionally, while 24-hour urine protein collection can show kidney damage and elevated serum creatinine may indicate kidney dysfunction, these results do not provide information about recent streptococcal infection specifically. Therefore, a positive ASO titer is the most relevant and specific result indicating recent exposure to Group A streptococcus in the context of postinfectious glomerulonephritis.