The sensitivity is higher in patients with interstitial nephritis induced by methicillin or when the Hansels stain is used. However, a 2013 study showed that the sensitivity and specificity of urine eosinophil testing are 35.6% and 68% respectively. Isosthenuria
Blood in the urine and occasional RBC casts
Sterile pyuria: white blood cells and no bacteria. About 50% of patients with AIN have pyuria. Nephrotic-range amount of protein in the urine may be seen with NSAID-associated AIN. Low grade proteinuria may be seen in a majority of other causes of AIN. White blood cell (WBC) casts: Fewer than one in five patients with AIN have WBC casts in urine. Pathology
While non-invasive patient evaluation (physical examination, blood and urine testing, imaging studies) can be suggestive, the only way to definitively diagnosis interstitial nephritis is with a tissue diagnosis obtained by kidney biopsy. Pathologic examination will reveal the presence of interstitial edema and inflammatory infiltration with various white blood cells, including neutrophils, eosinophils, and lymphocytes. Generally, blood vessels and glomeruli are not affected. Electron microscopy shows mitochondrial damage in the tubular epithelial cells, vacuoles in the cytoplasm, and enlarged endoplasmic reticulum. Gallium scan
The sensitivity of an abnormal gallium scan has been reported to range from 60% to 100%. A study of Gallium scan in 76 patients [23 with AIN, 8 with biopsy-proven AIN] showed an AUC of 0.75.
When the proximal tubule is injured, sodium, potassium, bicarbonate, uric acid, and phosphate reabsorption may be reduced or changed, resulting in low bicarbonate, known as metabolic acidosis, low potassium, low uric acid known as hypouricemia, and low phosphate known as hypophosphatemia. Damage to the distal tubule may cause loss of urine-concentrating ability and polyuria.In most cases of acute tubulointerstitial nephritis, the function of the kidneys will return after the harmful drug is discontinued, or when the underlying disease is cured by treatment. If the illness is caused by an allergic reaction, a corticosteroid may speed the recovery kidney function; however, this is often not the case. Chronic tubulointerstitial nephritis has no cure. Some patients may require dialysis. Eventually, a kidney transplant may be needed. Epidemiology
Interstitial nephritis is uncommon (<1% incidence) in patients without any symptoms but occurs in about 10-15% of hospitalized patients with acute kidney injury of unknown cause. While it can occur in patients of all ages, it is more common in elderly patients, perhaps due to increased exposure to drugs and other triggering causes. References
External links
Merck Manual