CASE STUDY 11-3 A 3-year-old girl was admitted with a diagnosis of acute lymphocytic leukemia. Her admitting labora- tory data are shown in Case Study Table 11-3.1. After admission, she was treated with packed cells, two 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 al- lopurinol 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. Questions 1. How would you explain the significant elevations of uric acid on admission? 2. What two factors are responsible for the normal levels of uric acid seen in subsequent admissions? 3. What is the most likely cause of the abnormally low level of urea nitrogen observed on 12/6? What other laboratory result would be useful to confirm your suspicions? CASE STUDY TABLE 11-3.1 LABORATORY RESULTS Urea N, mg/dL 10/1 10/2 10/3 10/4 11/14 12/6 6/20 12.0 * * 15 4.0 2.0 ★ Creatinine, mg/dL 0.7 ⋅ * 1.0 0.7 0.7 Uric acid, mg/dL 12.0 9.2 4.0 1.9 2.3 * 3.1 WBC, mm³ 56,300 3,700 2,800 3,700 Indicates test not performed. Creatine In muscle disease such as muscular dystrophy, polio- myelitis, hyperthyroidism, and trauma, both plasma cre- atine and urinary creatinine are often elevated. Plasma creatinine concentrations usually are normal in these pa- tients. Measurement of creatine kinase is used typically the liver in the production of urea. At normal physiologi pH. most ammonia in the blood exists as ammonium io (NH). Figure 11-5 shows the pH-dependent equilib nium between NH, and NH,. Ammonia is excreted a ammonium ion by the kidney and acts to buffer urine.