What is interstitial nephritis?

Interstitial nephritis is a rare condition that causes inflammation of the kidneys (numerous immune cells that normally fight infections invade the kidney).

In most cases, it is caused by a reaction to certain medications. These may include medicines that treat pain (nonsteroidal anti-inflammatory drugs or NSAIDs), antibiotics, and acid-lowering drugs.

Other causes of interstitial nephritis are infections and autoimmune diseases (conditions in which your immune system mistakenly attacks your body).

Diagnosing interstitial nephritis

Interstitial nephritis may not cause symptoms. Some people may have fatigue, a rash or fever. To diagnose interstitial nephritis your doctor may order urine and blood test but sometimes a kidney biopsy is required. For a kidney biopsy, your doctor will take a small sample from your kidney with a needle under local anaesthetic and under ultrasound or CT guidance to examine it under a microscope.

A unique subset of patients with interstitial nephritis have TINU syndrome (tubulointerstital nephritis with uveitis which is an inflammation of the eyes). The underlying mechanisms for TINU are not well understood.

Acid base and electrolyte disorders

The kidneys help maintain your body’s acid-base balance by excreting hydrogen ions into the urine and reabsorbing bicarbonate from the urine. Metabolic acidosis occurs if your body produces too much acid, if your kidneys are unable to reabsorb enough bicarbonate from the urine or if there is diminished acid excretion from the kidneys.

Some kidney related acidosis disorders (renal tubular acidosis) may cause kidney stones, osteopenia and even chronic kidney disease. The kidneys also help balance electrolyte concentrations of sodium, potassium, calcium, magnesium, chloride and phosphate. They filter electrolytes from the blood circulation, returning some to the blood and excreting any excess into the urine. Your doctor may be asked to investigate if there is evidence for any electrolyte imbalance.