A 3-year-old girl was admitted with a diagnosis of acute lymphocytic leukemia. After admission, she was treated by administration of packed red cells, 2 units of platelets, IV fluids, and allopurinol....

Extracted text: A 3-year-old girl was admitted with a diagnosis of acute lymphocytic leukemia. After admission, she was treated by administration of packed red cells, 2 units of platelets, IV fluids, and allopurinol. On the second hospital day, chemotherapy was begun, using IV vincristine and prednisone and intrathecal injections of methotrexate, prednisone, and cytosine arabinoside. She was discharged for home care 5 days later. She was continued on prednisone and allopurinol at home. She received additional chemotherapy 1 month later (11/1) and again on 11/14. On 12/6, she was readmitted because she had painful sores in her mouth and was unable to eat. LABORATORY RESULTS 10/1 10/2 10/3 10/4 11/14 12/6 6/20 Urea N 12.0 ** ** 15 4.0 2.0 ** (mg/dL) Creatinine 0.7 (mg/dL) 0.7 0.7 ** ** 1.0 ** Uric acid (mg/dL) 9.2 ** 12.0 4.0 1.9 2.3 3.1 WBC 56,300 3,700 ** ** ** 2,800 3,700 (mm2) **indicates test not performed Questions: 1. How would you explain the significant elevations of uric acid on admission? 2. Which two factors are responsible for the normal concentrations of uric acid seen in subsequent admissions? 3. Which is the most likely cause of the abnormally low concentration of urea nitrogen observed on 12/6? Which other laboratory test would confirm your suspicions?