Chapter 38: Chronic Tubulointerstitial Nephritis
A 39-year-old man is referred to you for the evaluation of glucosuria. The patient is not a diabetic and has had a recent hemoglobin A1c of 5.5%. Additional lab works reveal a serum glucose of 78 mg/dL, a creatinine of 1.7 mg/dL, a serum bicarbonate of 19 mmol/L, and a serum phosphate of 1.8 mg/dL. His urinalysis demonstrates 3+ glucose, 1+ protein, and trace leukocyte esterase. A protein to creatinine ratio shows 1.1 gm/gm creatinine. His urine sediment is bland with no cellular elements, casts, or crystals. His history is unremarkable and his father only has well-controlled hypertension. He works restoring older homes. How can you explain his laboratory findings?
A. Diabetic nephropathy (early stages)
B. Urinary tract infection
C. Chronic tubulointerstitial nephritis
D. Isolated glucosuria due to mutation in glucose transporter
The answer is C. The patient has laboratory findings consistent with CTIN, most likely from heavy metal exposure (lead) related to restoration of old homes. His creatinine is mildly elevated most likely indicating a long standing process with moderate fibrosis. His acidosis, glycosuria, hypophosphatemia, and proteinuria can all be explained by proximal tubular dysfunction. The disparity between the urinalysis and measured protein is most likely due to the fact that a urinalysis is only specific for albuminuria. With CTIN, patients may have more low molecular weight (nonalbumin) proteinuria that will only be picked up by direct quantification of total protein or with the sulfosalicylic acid reagent.
You are evaluating a 42-year-old man in the emergency room with AKI. Two weeks ago the patient had a presumed rotator cuff tear secondary to a sports related injury. Other than mild hypertension for which he is taking lisinopril 10 mg daily, the patient has no significant medical history. For the last 2 weeks he has been using ibuprofen 800 mg three times daily. Three days ago he developed nausea and diarrhea with a low-grade fever. The symptoms have since resolved but routine lab work for a shoulder MRI on the day of presentation demonstrated a creatinine of 4.2 mg/dL (prior baseline 1.6 mg/dL 3 months ago). Urinalysis shows 2–3 RBC/hpf and 1–2 WBC/hpf. There is 3+ protein. What is the most likely cause of the kidney injury in this patient?
A. Interstitial nephritis from NSAID use
B. Post-infectious glomerulonephritis from his recent infection
C. IgA nephropathy given his recent infection
D. Acute tubular necrosis
The answer is D. The patient will most likely have acute tubular necrosis from volume depletion ...