MOFFITT RENAL REPORT PEARLS 8/12/16: Interstitial Nephritis and Low Anion Gap!

Thanks to Bridget for presenting an interesting case involving a thought-provoking renal history, and to Kerry Cho for providing detailed insight into every part of it! Pearls below!


Top pearl from today: Interstitial nephritis can be acute or chronic! The causes are mostly the same for both, but some additional considerations for chronic forms.


For those interested in more details:

Interstitial nephritis ddx:

Acute: Medications altogether make up 75% of AIN cases!

  • Antibiotics (esp beta lactams, TMP-SMX, and rifampin)
  • NSAIDs
  • Diuretics (Lasix, thiazides)
  • PPIs
  • Other drugs: phenytoin, allopurinol, cimetidine, mesalamine
  • Infections: strep, EBV/CMV, histo, and many atypical infections
  • Immune: SLE, Sjogren, sarcoid, cryoglobulinemia
  • Tubulointerstitial nephritis and uveitis (TINU) syndrome (idiopathic, 5-10% of AIN)



Chronic: Ongoing exposure to the above meds/diseases can cause a chronic form. Also consider the additional causes below.

  • Obstructive uropathy
  • Vesicoureteral reflux
  • Analgesic nephropathy (acetaminophen, NSAIDs, ASA, codeine)
  • Heavy metals: Lead, mercury
  • Multiple myeloma
  • Gout

Tx: Withdraw offending agent or treat underlying cause, steroids if unresponsive. Consult renal for biopsy, particularly if dx not clear.


Low anion gap causes: Think increased unmeasured cations or decreased unmeasured anions!

Increased cations:

  • Plasma cell dyscrasias (paraproteins are positively charged)
  • Increased potassium, calcium, magnesium
  • Bromide or lithium toxicity
  • Severe hyperlipidemia (modern lab assays should account for this)

Decreased anions (think malnutrition):

  • Hypoalbuminemia (albumin is negatively charged)
  • Low phosphate

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