Renal stone and chronic kidney failure associated with hypouricemia: Questions

Excerpt

A 15-year-old boy was referred to our clinic as it was found that his renal function tests were increased. He presented with colic pain and a stone was detected that caused obstruction at his right ureter. After ureterorenoscopic lithotripsy was performed at another medical center, he was referred to our clinic. He did not have pain, fever, dysuria, hematuria, or reduced urinary output. His past medical history revealed that a kidney stone with a diameter of 10 mm was detected in the right kidney at 18 months of age and percutaneous lithotripsy was planned but could not be performed due to non-adherence of the family. His mother and father were first degree cousins; none of his family members had renal stones. According to his physical examination, his height was 162 cm (75 p), his weight was 46 kg (25–50 p), heart rate was 75 bpm, and blood pressure was 115/75 mmHg (95th percentile 130/83 mmHg). The patient appeared euvolemic and his urinary output was 2850 cc/m²/day. There was no abdominal tenderness with palpation. Systemic examination did not reveal any additional pathology. His laboratory examination results were as follows: blood urea nitrogen 58 mg/dl (N 9–23 mg/dl), serum creatinine 2.4 mg/dl (N 0.7–1.3 mg/dl), cystatin C 3.2 mg/L (N 0.62–1.11 mg/L), sodium 141 mEq/L (N 136–145 mEq/L), potassium 4.8 mEq/L (N 3.5–5.1 mEq/L), calcium 9.7 mg/dL (N 8.7–10.4 mg/dL), phosphorus 6.5 mg/dL (N 2.4–5.1 mg/dL), and serum uric acid 0.1 mg/dL (N 3.7–9.2 mg/dL). Cystatin C-based estimated glomerular filtration rate was calculated as 27 mL/min/1.73 m² (stage 4 chronic renal failure) using the Schwartz formula. His urinalysis results were pH 5, density 1007, protein 2+, hemoglobin 3+, and 102 erythrocyte/HPF and 10 leukocyte/HPF on microscopic analysis of the sediment. Fractional excretion of uric acid was 1.2% (N 7.3 ± 1.3%), calcium excretion 0.63 mg/kg/day (N 0.5–4 mg/kg/day), magnesium 119 mg/1.73 m²/day (N > 88 mg/1.73 m²/day), citrate 310 mg/1.73m²/day (N > 320 mg/1.73 m²/day), and oxalate 32 mg/1.73m²/day (N < 50 mg/1.73 m²/day). Nitroprusside test result was negative. Urinary excretion of cystine or dibasic amino acids were not increased in the urinary amino acid analysis. Chemical analysis of the stone revealed a xanthine stone. On USG examination, the right kidney size was 85 mm and the left kidney size was 102 mm (according to his age and height mean normal kidney size; right 92 mm, left 99 mm) [1]; right kidney AP pelvis diameter was 36 mm and there was SFU grade 4 PCD; left kidney AP pelvis diameter was 15 mm and there was SFU grade L PCD (minimal separation in renal sinus); there was no stone detected on USG. …