Definition
Acute tubulointerstitial nephritis (ATIN) is an acute inflammation of the renal interstitium and tubules that causes a decline in renal function over a period of days to weeks.
Etiology
Medications (most common)
- Antibiotics: β-lactams, sulfonamides, rifampin, fluoroquinolones
- NSAIDs
- Proton pump inhibitors and H2 blockers
- Loop diuretics and thiazides
- Anticonvulsants: phenytoin, valproate, carbamazepine, phenobarbital
- Other: allopurinol
Pathophysiology
- Immune-mediated tubulointerstitial damage (allergic interstitial nephritis) is the most widely accepted theory.
- Inflammatory infiltrates → tissue edema and tubular cell damage → compromised tubular flow
- Allergic interstitial nephritis: drugs act as haptens → type IV hypersensitivity reaction
- Acute obstruction: crystals (from e.g., uric acid, medications) or proteins (e.g., light chains) obstruct tubules
Clinical features
Clinical features of acute kidney injury, with or without:
- Morbilliform rash
- Fever
- Arthralgias
- Flank pain
Tip
The classic triad of fever, morbilliform rash, and eosinophilia is present in < 10% of patients with ATIN, but their presence can help to guide the diagnosis.
Diagnostics
- Blood tests
- BMP: ↑ BUN and creatinine
- CBC: ↑ eosinophils (more common in drug-induced ATIN)
- Urine studies
- Urinalysis
- Sterile pyuria
- Subnephrotic-range proteinuria
- Microscopic hematuria
- Urine microscopy
- WBC casts , RBC casts , waxy casts , granular casts , tubular epithelial casts
- Urine eosinophils (low sensitivity and specificity for ATIN)
- Urinalysis
Tip
Although frequently cited as a diagnostic clue, in clinical practice, urine eosinophils lack sensitivity and specificity for reliably confirming ATIN.