A 47-year-old man presented with slowly progressive chronic kidney disease (CKD) of unknown cause. He has a history of passing a kidney stone at age 30. A stone analysis was not performed at that time, and he has had no further stones. At age 40, his serum creatinine was 1.15 mg/dL; at age 47, the serum creatinine was 2.5 mg/dL. The man’s past history is otherwise unremarkable. Family history reveals that the patient’s sister was on dialysis for unknown cause. She underwent a kidney transplant several weeks previously and now has acute kidney failure. A biopsy is planned.
Physical examination is entirely unremarkable. Renal ultrasound findings are normal except for increased echogenicity of the kidneys. A urinalysis was negative, and laboratory findings were consistent with chronic kidney disease. Given the uncertainty of the case, his physician reviewed the urinalysis personally. Microscopic examination revealed the presence of brown crystals (figure 1). A senior laboratory technician recalled seeing similar crystals from another case some time ago involving an infant who presented with acute kidney injury (AKI).