What laboratory finding is indicative of rheumatic heart disease?

The presence of a positive antistreptolysin titer is a significant laboratory finding indicating rheumatic heart disease. This titer assesses the levels of antibodies against streptolysin O, a toxin produced by group A Streptococcus bacteria. Elevated levels suggest a prior infection with this bacterium, which is closely associated with rheumatic fever—a complication that can lead to rheumatic heart disease.

When an individual has a recent streptococcal infection, the immune system produces antibodies to combat the infection. If left untreated, this can lead to immune-mediated processes that damage the heart, resulting in rheumatic heart disease. Therefore, a positive antistreptolysin titer not only indicates a recent infection but also connects the involved immune response to potential cardiac damage.

In terms of the other options: a negative C-reactive protein would not suggest inflammation or infection, an increased reticulocyte count is more indicative of a response to anemia rather than a specific infection, and a low erythrocyte sedimentation rate (ESR) indicates reduced inflammation, which would not align with the findings one would expect with rheumatic heart disease. Thus, the positive antistreptolysin titer is the relevant laboratory finding associated with the disease process.