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?