Alternative names
Tubulointerstitial nephritis; Nephritis - interstitial; Acute interstitial (allergic) nephritis

Definition
Interstitial nephritis is a kidney disorder caused by inflammation of the tubules and the spaces between the tubules and the glomeruli.

Causes, incidence, and risk factors
Interstitial nephritis involves inflammation of the spaces between the renal tubules and may include inflammation of the tubules. It may be a temporary lesion, most often associated with the effects of various medications on the kidney, or it may be chronic and progressive.

Interstitial nephritis is one of the lesions associated with analgesic nephropathy, and can also occur with allergic reaction to a drug (acute interstitial allergic nephritis) or as a side effect of medications. Medications commonly associated with interstitial nephritis include antibiotics such as penicillin, ampicillin, methicillin, sulfonamide medications, and others. Other medications include nonsteroidal anti inflammatory drugs, furosemide, and thiazide diuretics. The disorder may occur 2 or more weeks after exposure to the medication.

Interstitial nephritis causes reduction in kidney function, ranging from mild dysfunction to acute kidney failure. About one-half of the cases will exhibit decreased urine output and other signs of acute renal failure. The kidney may fail to concentrate the urine when water intake is reduced. The kidney may fail to regulate acid/base levels of the body may be reduced, with failure to excrete acid appropriately in the urine. Metabolic acidosis may occur because of the inability to excrete acid. The disorder may progress to chronic renal failure or end-stage renal disease.

The acute form of interstitial nephritis is common and may account for approximately 15% of cases of acute kidney failure. Risks include exposure to medications that may have nephrotoxic effects. The disorder may be more severe and more likely to lead to chronic or permanent kidney damage in the elderly.

Symptoms

 
• Increased or decreased urine output  
• Fever  
• Mental status changes, ranging from drowsiness to confusion to coma  
• Nausea, vomiting  
• Rash (sometimes)  
• Swelling of the body, any area  
• Weight gain (from fluid retention)  
• Blood in the urine

Signs and tests
An examination may reveal edema or fluid overload, or signs of volume depletion, with abnormal sounds heard when listening with a stethoscope (auscultation) to the heart or lungs. The blood pressure commonly is high.

 
• A urinalysis shows small amounts of protein and sometimes red blood cells, renal tubular cells, and other abnormalities. The excretion of protein in the urine is not as severe as with nephrotic syndrome.  
• WBCs and WBC casts in the urine (particularly eosinophils) are often seen.  
• CBC may demonstrate eosinophilia (higher than normal eosinophil count).  
• Urine specific gravity and osmolality show there is a failure to concentrate urine even when water intake is restricted.  
• Urine pH may show a failure to acidify urine appropriately.  
• Arterial blood gases and blood chemistry may show metabolic acidosis.  
• BUN and creatinine levels are used to assess level of kidney functioning.  
• RBC - urine shows increased red blood cells indicating kidney disease.  
• A kidney biopsy confirms the diagnosis of interstitial nephritis and is used to evaluate the extent of damage to the kidney.

Treatment
Treatment focuses on treating underlying causes and relieving symptoms. Avoiding the suspect medications may cause the symptoms to go away quickly.

Dietary restriction of sodium (salt) and fluid may control swelling and hypertension. Dietary restriction of protein may be needed to control azotemia (accumulation of nitrogenous waste products in the blood) associated with acute renal failure.

If dialysis is necessary, it usually is required for only a short time.

Corticosteroids or anti-inflammatory medications may be of benefit in some cases.

Expectations (prognosis)
Most often, interstitial nephritis is an acute but short-term disorder. On rare occasions it may cause permanent damage including chronic renal failure.

Complications

 
• Acute renal failure  
• Chronic renal failure

Calling your health care provider
Call your health care provider if symptoms indicate interstitial nephritis may be present.

If you have interstitial nephritis, call if new symptoms develop, especially decreased alertness or decrease in urine output.

Prevention
In many cases, the disorder may not be preventable. Avoiding or minimizing the use of associated medications may help reduce risk.