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Chapter 37: Acute Tubulointerstitial Nephritis

A 50-year-old Caucasian woman with a 30-year history of type 1 diabetes presents to the nephrology office for routine follow-up of proteinuria. She works as a marketing executive at a beauty product firm. She is asymptomatic. She is on an insulin pump for diabetes, on losartan for proteinuria and has started omeprazole 6 months ago for endoscopically diagnosed reflux esophagitis. On her last ophthalmological examination, she had mild non-proliferative diabetic retinopathy. Her vital signs show a blood pressure of 130/80. Her physical examination is unremarkable. On laboratory examination, her creatinine has increased from 1 to 1.4 mg/dL and her eGFR has dropped from 66 to 40 mL/min/1.73 m2 over the past year. On review of her past records, her creatinine had increased from 0.7 to 1 mg/dL over 10 years. Hemoglobin A1c is 6.5%. Urinalysis shows 1+ protein and 0–5 white blood cells/HPF. Rest of her serum tests are normal. What is the best next step in management of this patient?

A. Follow-up in 1 year

B. Urine eosinophil testing

C. Refer to endocrinology for better control of diabetes

D. Refer to ophthalmology for follow-up of diabetic retinopathy

E. Discuss renal biopsy to rule out drug-induced tubulointerstitial nephritis

The answer is E. Faster than usual progression in the setting of existing CKD should prompt evaluation of drug-induced tubulointerstitial nephritis, particularly in the setting of an offending medication. This patient, with CKD stage 2, had fairly stable eGFR until she started taking omeprazole. She also has white blood cells in her urine, which support a diagnosis of drug-induced tubulointerstitial nephritis. Thus, the possibility of a kidney biopsy should be considered in this patient.

Follow-up in 1 year is not recommended in this patient who has lost 26 mL/min of eGFR in a year. Urine eosinophil is not accurate for ATIN diagnosis and is often misleading. The diabetes is fairly well controlled and change in diabetes care is not necessary. The patient has known nonproliferative diabetic retinopathy and follow-up with ophthalmology is not necessary at this time.

A 75-year-old African–American man is admitted to the hospital for fever and elevated white blood cell count with diagnosis of cellulitis of left foot. His past medical history is significant for extensive atherosclerotic vascular disease including coronary artery disease requiring a drug-eluting stent to his left anterior descending artery and peripheral vascular disease. He is treated with ampicillin-sulbactam leading to improvement in cellulitis. On day 3 of his hospitalization he has a new rash and his serum creatinine increases from baseline of 1–1.5 mg/dL. Nephrology is consulted and a kidney biopsy is performed. Review of ...

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