Do Not Dismiss Incidental Hyperkalemia in Childhood: Early Recognition of Pseudohypoaldosteronism Type II.

Persistent hyperkalemia in children warrants careful evaluation, as it may indicate an underlying renal tubular disorder. We report a case of persistent hyperkalemia in a three-year-old boy in which adenovirus infection unmasked latent pseudohypoaldosteronism type II (PHAII), allowing recognition prior to the development of hypertension. The patient presented with a nine-day history of fever. Initial laboratory tests showed hyperkalemia (5.8 mmol/L), mild hyponatremia, normal renal function, and normal anion gap (AG) metabolic acidosis (pH: 7.37; bicarbonate: 19.9 mmol/L; AG: 8.1 mmol/L). The patient was diagnosed with adenovirus infection. Although the fever and inflammatory markers improved within four days, the hyperkalemia persisted (6.2 mmol/L). At three and six weeks, serum potassium remained elevated (6.0 and 6.4 mmol/L, respectively) with normal AG metabolic acidosis (HCO₃⁻ 20.0 and 17.6 mmol/L, respectively; AG 12.8 and 11.4 mmol/L, respectively). Urinary potassium indices showed inappropriately low fractional excretion of potassium (FEK) and transtubular potassium gradient (TTKG) with normal renin-aldosterone levels. Subsequently, family history-taking identified early-onset hypertension in the child's father. Treatment with hydrochlorothiazide (HCTZ) resulted in normalization of serum potassium and correction of the metabolic acidosis. Genetic testing revealed a heterozygous