A 29-year-old man has developed marked joint pain beginning 12 days after receiving snake antivenom injection. On physical examination, there is diffuse joint pain with movement. The stool is negative for occult blood. Laboratory studies show a serum creatinine level of 4.4 mg/dL and urea nitrogen level of 42 mg/dL. Microscopic examination of a renal biopsy specimen shows focal fibrinoid necrosis of the small arterial and arteriolar vascular media and intravascular microthrombi. Scattered neutrophils are seen in these areas of necrosis. Which of the following laboratory findings in the blood is most likely present in this patient?
Correct Answer: Hypocomplementemia
Description: In the localized immune complex reaction (Arthus reaction) at the site of injection, there can be activation and depletion of complement C3. The reaction described here is serum sickness in response to the injected foreign protein, and produced more widespread antigen-antibody complex deposition, particularly in the kidneys. CD4+ lymphocytes assist in various antibody-mediated and cell-mediated immune reactions, but their numbers in peripheral blood do not change appreciably. IgE concentration is increased in individuals with atopy and the potential for type I hypersensitivity. Although neutrophils are being recruited locally to the inflammatory reaction in this case, they are not depleted systemically, and they may be increased in the circulation. Thrombocytopenia could be seen with a thrombotic microangiopathy such as thrombotic thrombocytopenic purpura, but not typically in an Arthus reaction.
Category:
Pathology
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