Hypernatremia and Hypophosphatemia in Distal Renal Tubular Acidosis: A Case Report of Acid-base and Electrolyte Misadventure

Abstract Introduction: Distal renal tubular acidosis (RTA) is easily recognized in patients with hypokalemia and normal anion gap acidosis. Other concurrent electrolyte abnormalities could change the diagnosis. We describe a newly diagnosed distal RTA complicated with severe hypernatremia and hypophosphatemia while admitted to the intensive care unit. Case report: A 12-year-old girl presented with worsening paralysis. Initial investigations revealed low serum potassium of 1.8mmol/L, pH 7.2mmol/L, bicarbonate 12mmol/L and high urine pH (8.0) suggesting distal RTA. She required mechanical ventilation due to severe metabolic acidosis and hypokalemia. Resuscitation strategies initially focussed on intravenous hydration with 0.9% normal saline and potassium repletion. Delayed correction of acidosis with sodium bicarbonate led to severe hypernatremia (180mmol/L) and slow recovery of serum potassium level. Hypernatremia was also contributed by concurrent nephrogenic diabetes insipidus. Interestingly, her serum phosphate was persistently low (0.4mmol/L) leading to more workup to investigate proximal tubulopathy. It persisted till resolution of hypernatremia and acidosis. Meanwhile she developed sepsis with multiple thromboses attributed to disseminated tuberculosis. Screening for connective tissue diseases were negative. She recovered well and was discharged with anti-tuberculosis drugs, anticoagulation and potassium supplements. Conclusion: In conclusion, correction of acidosis in distal RTA should be prioritised to avoid prolonged hypokalemia and significant increase in serum sodium. Hypophosphatemia in a critically ill patient should be interpreted with caution, correlating with serum sodium and arterial blood gas to avoid incorrect diagnoses.