Diagnosis of RTA Suspected in patients with metabolic acidosis with normal anion gap or with unexplained hyperkalemia Serum and urine pH, electrolyte levels, and osmolalities Often, testing after stimulation (eg, with ammonium chloride, bicarbonate, or a loop diuretic) RTA is suspected in any patient with unexplained metabolic acidosis (low plasma bicarbonate and low blood pH) with normal anion gap.