The patient's laboratory examination revealed a white blood cell count of 60.3 × 103/µL (reference range, 3.4-9.6 × 103/µL) consisting of 80% atypical lymphocytes characterized by cerebriform nuclei (Figure 4). Flow cytometry of a peripheral blood sample revealed T cells expressing the αβ T-cell receptor with the following abnormalities: coexpression of CD4 and CD8, uniformly strong expression of CD7, and weak expression of CD25. The sedimentation rate was elevated at 50 mm/h (50 mm/h; reference value, <40 mm/h) as were the levels of serum urea nitrogen (32 mg/dL [11.4 mmol/L]; reference range, 8-22 mg/dL [2.9-7.9 mmol/L]) and serum creatinine (2.5 mg/dL [221 µmol/L]; 0.7-1.3 mg/dL [62-115 µmol/L]). Serologic tests were negative for human T-cell lymphotropic virus 1.