A 48-year-old woman was referred to a nephrology clinic for elevated creatinine. Routine labs showed serum creatinine level of 1.5 mg/dL with an estimated glomerular filtration rate (eGFR) of 37.5 mL/min/1.73 m2. The patient reported being unaware of any history of chronic kidney disease (CKD). She has had diabetes for the past 10 years and a history of hyperlipidemia and morbid obesity. She had lost more than 100 lbs about 5 years earlier through diet and exercise, and she has since stopped taking metformin. Current medications included atorvastatin and vitamin D supplement 2000 units daily. She has also been taking vitamin C 3000 mg/d for “general health benefit” for the past 10 years.
Additional lab tests showed:
- Urine protein/creatinine ratio 0.5 g/g
- Albumin/creatinine ratio 326 mg/g
- Urinalysis positive for protein and negative for blood
- Hemoglobin 11 g/dL
- Anti-nuclear antibody negative.
- Complement C3 level 91 (normal 83-193 mg/dL)
- Complement C4 level 25 (normal 15-57 mg/dL)
- Hemoglobin A1c 5.6
Kidney ultrasound imaging showed bilaterally echogenic kidneys, with the right and left kidney measuring 10.5 and 10.6 cm in length, respectively. A nephrologist obtained prior records, which showed she had a serum creatinine level of 1.4 mg/dL 5 years earlier. A kidney biopsy revealed numerous oxalate crystal deposits in the tubulointerstitium with surrounding inflammation.