Something you took is attacking your kidneys.
Acute interstitial nephritis is an allergic reaction — not in the skin, but in the tissue between the kidney's tubules. It is one of the more common causes of unexplained acute kidney injury, and it is reversible if the drug is stopped in time.
Two things almost nobody does
Nobody checks the differential for eosinophils.
A complete blood count with differential is one of the cheapest tests in medicine, and peripheral eosinophilia — an elevated eosinophil count in the blood — is a real clue in drug-induced interstitial nephritis. It is absent in many cases, so it cannot exclude the diagnosis. But when present in a patient with an unexplained rising creatinine, it points directly at an allergic process, and it is sitting in a lab result nobody scrolled down to read.
(Note the distinction: urine eosinophils are a different test, are neither sensitive nor specific, and have been abandoned. Peripheral eosinophilia is what to look at.)
And nobody reconstructs the medication list.
The timeline is the diagnosis. A drug started days to weeks before the creatinine rose is the answer, and finding it requires asking about over-the-counter products, supplements, and anything stopped last month — not reading the problem list.
A proton pump inhibitor bought at a pharmacy counter and taken for three years will never appear on a medication reconciliation, and it is now among the leading causes.
Board-certified nephrology at Remix Medical in Houston. Call (713) 597-5131 or book online.
The drugs
Proton pump inhibitors. Omeprazole, pantoprazole, and the rest. The ones patients never suspect, because they are sold over the counter and taken for years without a thought.
NSAIDs. Ibuprofen, naproxen. They injure the kidney by two separate mechanisms, and this is one of them.
Antibiotics. Penicillins, cephalosporins, sulfa drugs, rifampin, ciprofloxacin.
Checkpoint inhibitors. Pembrolizumab, nivolumab. Increasingly common as cancer immunotherapy expands.
Allopurinol, diuretics, phenytoin, mesalamine.
Infection and autoimmune disease — sarcoidosis, Sjögren's, lupus — cause it too. But the answer is a medication far more often than not.
The classic triad rarely appears
Textbooks describe fever, rash, and eosinophilia. Fewer than ten percent of patients have all three. Waiting for that combination means missing the diagnosis.
Most patients present with nothing but a rising creatinine on a routine blood test. That is the whole presentation — which is exactly why the eosinophil count and the medication history carry so much weight.
What we look for
White cell casts on urine microscopy — clumps of white cells formed in the tubules. Sterile pyuria, meaning white cells in the urine with no infection. Mild proteinuria, usually well under a gram.
And a medication started days to weeks before the creatinine rose. The timeline is the diagnosis. Reconstructing it carefully, including over-the-counter drugs and things stopped last month, is most of the work.
Why the biopsy question matters
Interstitial nephritis is treated with corticosteroids. Acute tubular necrosis, which can look identical, is not — and steroids in that setting cause harm without benefit.
When the diagnosis is uncertain and steroids are being considered, tissue settles it. We determine whether a biopsy is warranted, confirm it is safe, and coordinate the procedure with an interventional radiologist. We interpret the pathology.
Treatment
Stop the drug. This is the treatment. Most patients recover once the offending agent is removed, and no other intervention matters as much.
Corticosteroids for patients who do not improve within a week, or who have severe injury. Early treatment predicts better recovery. Weeks of delay allow interstitial inflammation to become interstitial fibrosis, which does not reverse.
Never restart the drug. Re-exposure can cause a more severe reaction.
Recovery
Most patients recover most of their function. Not everyone recovers fully. Prolonged injury before the diagnosis is made — which happens when a proton pump inhibitor is never questioned — leaves permanent scarring.
The patients who do best are the ones whose medication list was reviewed early.
If your creatinine rose and nobody asked what you buy at the pharmacy — or looked at your eosinophil count — the diagnosis has not been pursued.
Call (713) 597-5131 or book online.