A 49-year-old man with past medical history of chronic kidney disease (CKD), diabetes, hypertension, and obesity who underwent bariatric surgery 2 years previously was referred to the nephrology clinic for worsened kidney function found on routine testing. His serum creatinine was 1.2 mg/dL a year ago and now is 3.55 mg/dL. He feels well and has had no recent illnesses. He does not take any pain medications such as non-steroidal anti-inflammatory drugs. He has a healthy die and drinks a cup of leafy green vegetable smoothies every day. His diabetes has been well controlled, with hemoglobin A1c ranging from 5.5 to 6.5 in the past year. His blood pressure is also well controlled (less than 130/80 mm Hg). His medications include lisinopril-hydrochlorothiazide, rosuvastatin, metformin, and vitamin C. Physical examination was unremarkable. Lisinopril-hydrochlorothiazide and metformin were held. He was placed on amlodipine and glipizide for blood pressure and diabetes control, respectively. Repeat serum creatinine was higher at 4.0 mg/dL. Further workup demonstrated the following:
- Urinalysis is 1+ positive for protein and blood
- Urine protein/creatinine ratio is 1.1 g/g and albumin/creatinine ratio is 567 mg/g
- Urine sediment showed few granular cell casts
- Serum calcium 8.6 mg/dL, phosphorus 6.2 mg/dL (normal 2.7-4.5 mg/dL)
- Liver function tests and pancreatic enzymes are normal.
- Serum protein electrophoresis showed no paraproteins.
- All serologies were negative, including ANA, ANCA, anti-glomerular basement membrane (anti-GBM), dsDNA, HBV, HCV, HIV, RPR, cryoglobulin.
- Complement C3 and C4 are both normal
A kidney ultrasound showed bilateral echogenic kidneys with no evidence of hydronephrosis or kidney stones. The right kidney measured 12.73 cm in length and the left kidney measures 14.33 cm in length.
A kidney biopsy revealed acute tubular injury with extensive intratubular and interstitial deposit of calcium oxalate crystals. There is background mild diabetic kidney disease. Degree of interstitial fibrosis and tubular atrophy is moderate. 24-hour urine oxalate is 104 mg/day (normal <45 mg/day). Urine oxalate/creatinine ratio is 151 mg/g (normal 3-30 mg/g).