Distal Renal Tubular Acidosis Screening by Urinary Acidification Testing in Mexican Children

Norma E. Guerra-Hernández, Department of Pediatric Nephrology, Hospital General del Centro Médico Nacional �??La Raza�?�, Instituto Mexicano del Seguro Social (IMSS), México, D.F., Mexico
Karen V. Ordaz-López, Department of Pediatric Nephrology, Hospital General del Centro Médico Nacional �??La Raza�?�, Instituto Mexicano del Seguro Social (IMSS), México, D.F., Mexico
Laura Escobar-Pérez, Department of Physiology, Facultad de Medicina, Universidad Nacional Autónoma de México, México, D.F., Mexico
Circe Gómez-Tenorio, Department of Pediatric Nephrology, Hospital General del Centro Médico Nacional �??La Raza�?�, Instituto Mexicano del Seguro Social (IMSS), México, D.F., Mexico
Víctor M. García-Nieto, Department of Pediatric Nephrology, Hospital Universitario �??Nuestra Señora de La Candelaria�?�, Santa Cruz de Tenerife, Spain

Background: Primary distal renal tubular acidosis is a clinical disorder characterized by hyperchloremic metabolic acidosis, hypercalciuria, hypocitraturia, urinary acidification impairment, hypokalemia, metabolic bone disease, and nephrocalcinosis. Urinary acidification ability may be evaluated by an acidification test or maximum urinary pCO2 assessment with alkaline urine. The maximum urinary pCO2 test using acetazolamide and sodium bicarbonate is an easy test to confirm the lack of urine acidification in distal renal tubular acidosis in children. Objective: To determine the urinary acidification ability using the maximum urinary pCO2 assessment in a group of children with a distal renal tubular acidosis diagnosis. Material and methods: Thirty children were evaluated (13 males and 17 females); 23 children had been diagnosed with distal renal tubular acidosis by other physicians and were under alkali treatment with potassium and sodium citrates (21) and bicarbonate (2), and five children were not under alkali treatment. Two children had been diagnosed with primary distal renal tubular acidosis by our medical group. The maximum urinary pCO2 was determined by the oral intake of acetazolamide and sodium bicarbonate. Results: Two cases with primary distal renal tubular acidosis were found, and they had a history of dehydration episodes during infancy and showed hyperchloremic metabolic acidosis with hypokalemia. They also exhibited urine acidification impairment with furosemide and reduced urinary pCO2 (< 60 mmHg), and the urine-blood pCO2 gradient was reduced in both cases (< 30 mmHg). One of them developed bilateral sensorineural deafness, while the other showed severe hypocitraturia. One case of proximal or type 2 renal tubular acidosis with hyperaminoaciduria was identified. Twenty-eight children displayed normal urinary acidification and did not show signs of distal renal tubular acidosis. Conclusions: The urinary acidification test with furosemide and urinary pCO2 assessment are reliable tests to identify the renal excretion of hydrogen ions (H+) and allow confirmation of the lack of urine acidification in distal renal tubular acidosis.

Keywords: Acidosis. Distal renal tubular acidosis. Nephrocalcinosis. Proximal renal tubular acidosis. Urinary acidification. Urinary acidification test.