What laboratory result is characteristic of a serum sickness-like reaction?

A serum sickness-like reaction is characterized by the development of certain laboratory findings due to immune complex formation triggered by an antigen exposure, typically after the use of certain medications (like antibiotics) or infections. One of the hallmark features of this reaction is an increase in acute phase reactants, particularly C-reactive protein (CRP).

CRP is a protein produced by the liver in response to inflammation, and its levels rise significantly during an inflammatory response. In the context of a serum sickness-like reaction, the presence of immune complexes leads to a systemic inflammatory response, resulting in elevated CRP levels. This increase serves as a biomarker for the inflammatory process occurring within the body.

In this scenario, the other laboratory results listed are not typical for serum sickness-like reactions. Elevated bilirubin could indicate liver dysfunction or hemolysis but is not a direct marker of the immune response. A decreased reticulocyte count suggests a lack of bone marrow response to anemia, which may not correlate directly with the immune response seen in serum sickness. A high platelet count may occur in various conditions, including inflammatory states; however, it is not specifically indicative of serum sickness-like reactions.

Thus, the elevation of C-reactive protein is the most fitting and characteristic finding in