Q. A 6-year-old male is admitted to the hospital with a 3-day history of fever, pain, and swelling in his right leg. The fever is associated with chills and rigors. His parents report that he has also had multiple skin and soft tissue infections over the past few months, which have been treated with antibiotics, but have not completely resolved. The patient has no other significant medical history, and he has not received any immunizations recently. On examination, the patient is febrile with a temperature of 39 degrees Celcius. His right leg is swollen and tender, with erythema and warmth. There are multiple skin abscesses on his arms and legs, which are draining pus. The patient's vital signs are stable, and the rest of this physical examination is unremarkable. Laboratory tests show leukocytosis with a white blood cell count of 18,000/mm3, with neutrophilia. The C-reactive protein level is elevated at 120 mg/L. Blood cultures are obtained, and you start the patient on intravenous antibiotics. A complete blood count with differential and a blood smear is performed. The blood smear shows neutrophilia with normal morphology. You are concerned for an immunodeficiency disorder involving both B and T cells and order immunological testing. Which of the following additional findings would most support a diagnosis of leukocyte adhesion deficiency?