A 34-year-old male who is being treated for acute leukemia develops oliguria. His serum creatinine level is 2.7 mg/dL. Renal biopsy reveals multiple uric acid crystals obstructing renal tubular lumen. The principal site of uric acid precipitation would be which of the following?

Question

A 34-year-old male who is being treated for acute leukemia develops oliguria.  His serum creatinine level is 2.7 mg/dL.  Renal biopsy reveals multiple uric acid crystals obstructing renal tubular lumen.  The principal site of uric acid precipitation would be which of the following?

Quizplus · Accepted Answer

Tumor lysis syndrome is an oncologic emergency. It often develops during chemotherapy for high-grade lymphomas, leukemias, and other tumors that have rapid cell turnover and high sensitivity to chemotherapy. When a large number of tumor cells are destroyed during chemotherapy, intracellular ions, such as potassium, phosphorous, and uric acid (a metabolite of tumor nucleic acid), are released into the serum and are then filtered by the kidneys. Uric acid (pKa = 5.4) is soluble at physiologic pH, but precipitates in an acidic environment. The lowest pH along the nephron is found in the distal tubules and collecting ducts; so these are the segments of the nephron that become obstructed by uric acid crystals. Obstructive uropathy and acute renal failure follow. The risk of tumor lysis syndrome can be reduced by urine alkalinization and hydration. Additionally, allopurinol (a xanthine oxidase inhibitor) is used to reduce uric acid production during the breakdown of tumor cells. (Choice D) Ignore the anatomy portion of choice D and evaluate the latter portion. A "high urine flow rate" would universally decrease uric acid crystallization and precipitation. Therefore, this cannot possibly be the correct answer. (Choices A, B and C) Uric acid does not precipitate in proximal tubules or in Henle's loop. Educational Objective: Tumor lysis syndrome occurs when tumors with a high cell turnover are treated with chemotherapy. The lysis of tumor cells causes intracellular ions, such as potassium and phosphorous, and uric acid (metabolite of tumor nucleic acid) to be released into serum. Uric acid is soluble at physiologic pH, but it can precipitate in the normally acidic environment of distal tubules and collecting ducts. The prevention of tumor lysis syndrome includes urine alkalinization and hydration, as high urine flow and high pH along the nephron prevents crystallization and precipitation of uric acid.

A 34-Year-Old Male Who Is Being Treated for Acute Leukemia