The history should focus on identification of an offending agent within the two weeks before the onset of symptoms, or, in the case of potential repeat exposure, within the few days before presentation. Note that in patients previously sensitized to the antigen, symptoms may develop within a few days of re-exposure to the causative agent.Ī thorough history and physical exam are essential in the evaluation of suspected serum sickness. It is the process of clearing these immune complexes and the subsequent inflammatory reaction that coincides with the onset of clinical symptoms. Also, the activation of the complement system will trigger histamine release and increase vascular permeability, which leads to an inflammatory response in the tissues and joints. These levels can be used to differentiate serum sickness from a serum sickness-like reaction, which will have normal complement levels.
The deposition of immune complexes may also activate the classical complement pathway, leading to lower levels of circulating C3 and C4. If the macrophage activating system is not functioning properly, these complexes will become saturated in the circulation, leading to immune complex deposition, most commonly in parenchymal tissues and synovial joint fluid. When a patient is exposed to a foreign serum protein, it takes approximately 6-10 days for antibodies to develop and form antigen-antibody complexes and is considered a Type III immune-mediated hypersensitivity reaction.