Other useful measurements include the following: Fractional excretion of bicarbonate (HCO 3) in evaluation of renal tubular acidosis Chloride (Cl) levels for diagnosis of metabolic alkalosis Urine anion gap in evaluation of metabolic acidosis Potassium (K) levels in determining the cause of hypokalemia or hyperkalemia Levels of sodium, calcium, magnesium, uric acid, oxalate, citrate, and cystine in evaluation of calculi Eosinophils, cells that stain bright red or pink-white with Wright or Hansel staining, most commonly indicate one of the following: Acute interstitial nephritis Rapidly progressive glomerulonephritis Acute prostatitis Renal atheroembolism Cytology is used for the following: To screen for cancer in high-risk populations (eg, petrochemical workers) To evaluate persistent painless hematuria of unclear etiology after cystoscopy in the absence of glomerular disease (suggested by the absence of dysmorphic RBCs, proteinuria, and renal failure) in patients with irritative voiding symptoms Sensitivity is about 90% for carcinoma in situ; however, sensitivity is considerably lower for low-grade transitional cell carcinomas.