Pediatric Nephrology
PediatrNephrol (1990) 4: 268- 275 9 IPNA 1990
Practical pediatric nephrology Renal tubular acidosis Juan Rodriguez-Soriano and Alfredo Vallo Departmentof Paediatrics,HospitalInfantilde Crucesand BasqueUniversitySchoolof Medicine,Bilbao,Spain ReceivedNovember3; acceptedNovember7, 1989
Abstract. The term renal tubular acidosis (RTA) is applied to a group of transport defects in the reabsorption of bicarbonate (HCO3-), the excretion of hydrogen ions, or both. On clinical and pathophysiological grounds, RTA can be separated into three main types: distal RTA (type 1), proximal RTA (type 2) and hyperkalaemic RTA (type 4). Some patients present combined types of proximal and distal RTA or of hyperkalaemic and distal RTA. Diagnosis of RTA should be suspected when a patient presents a normal plasma anion gap, and hyperchloraemic metabolic acidosis. A normal plasma anion gap (Na+-[CI-+HCO3-] = 8-16 mE@) reflects loss of HCO3- from the extracellular fluid via the gastro-intestinal tract or the kidney, dilution of extracellular buffer or administration of hydrochloric acid (HC1) or its precursors. Distinction of RTA from other disorders is greatly facilitated by the study of the urine anion gap (Na§ This index estimates the urinary concentration of ammonium in a patient with hyperchloraemic metabolic acidosis. A negative urine anion gap (CI- >>Na++K+) suggests the presence of gastro-intestinal or renal loss of HCO3-, whiIe a positive urine anion gap (C1- 1 0 15%). This HCO3- wasting is a transient phenomenon and a steady state is again maintained when plasma HCO3concentration stabilizes in the acidaemic range.
270 Proximal RTA may occur in children as a primary and isolated entity [27] or accompanied by other proximal tubular defects (Fanconi syndrome [28]). Stunted growth is the most prominent clinical feature. Rickets and osteomalacia are never observed unless hypophosphataemia is present as occurs in the Fanconi syndrome [29]. Nephrocalcinosis and urolithiasis are never observed, even in situations in which hypercalciuria is present [29]. Hypokalaemia and related symptoms are also restricted to cases with the Fanconi syndrome.
Distal RTA (type 1) This type is caused by impaired distal acidification and is characterized by the inability to lower urine pH maximally (below 5.5) under the stimulus of systemic acidaemia. The impaired excretion of NH4§ is secondary to this defect. In general, HCO3- reabsorption is quantitatively normal but, as a consequence of the elevated urine pH, a certain degree of bicarbonaturia may be obligatorily present (
PediatrNephrol (1990) 4: 268- 275 9 IPNA 1990
Practical pediatric nephrology Renal tubular acidosis Juan Rodriguez-Soriano and Alfredo Vallo Departmentof Paediatrics,HospitalInfantilde Crucesand BasqueUniversitySchoolof Medicine,Bilbao,Spain ReceivedNovember3; acceptedNovember7, 1989
Abstract. The term renal tubular acidosis (RTA) is applied to a group of transport defects in the reabsorption of bicarbonate (HCO3-), the excretion of hydrogen ions, or both. On clinical and pathophysiological grounds, RTA can be separated into three main types: distal RTA (type 1), proximal RTA (type 2) and hyperkalaemic RTA (type 4). Some patients present combined types of proximal and distal RTA or of hyperkalaemic and distal RTA. Diagnosis of RTA should be suspected when a patient presents a normal plasma anion gap, and hyperchloraemic metabolic acidosis. A normal plasma anion gap (Na+-[CI-+HCO3-] = 8-16 mE@) reflects loss of HCO3- from the extracellular fluid via the gastro-intestinal tract or the kidney, dilution of extracellular buffer or administration of hydrochloric acid (HC1) or its precursors. Distinction of RTA from other disorders is greatly facilitated by the study of the urine anion gap (Na§ This index estimates the urinary concentration of ammonium in a patient with hyperchloraemic metabolic acidosis. A negative urine anion gap (CI- >>Na++K+) suggests the presence of gastro-intestinal or renal loss of HCO3-, whiIe a positive urine anion gap (C1- 1 0 15%). This HCO3- wasting is a transient phenomenon and a steady state is again maintained when plasma HCO3concentration stabilizes in the acidaemic range.
270 Proximal RTA may occur in children as a primary and isolated entity [27] or accompanied by other proximal tubular defects (Fanconi syndrome [28]). Stunted growth is the most prominent clinical feature. Rickets and osteomalacia are never observed unless hypophosphataemia is present as occurs in the Fanconi syndrome [29]. Nephrocalcinosis and urolithiasis are never observed, even in situations in which hypercalciuria is present [29]. Hypokalaemia and related symptoms are also restricted to cases with the Fanconi syndrome.
Distal RTA (type 1) This type is caused by impaired distal acidification and is characterized by the inability to lower urine pH maximally (below 5.5) under the stimulus of systemic acidaemia. The impaired excretion of NH4§ is secondary to this defect. In general, HCO3- reabsorption is quantitatively normal but, as a consequence of the elevated urine pH, a certain degree of bicarbonaturia may be obligatorily present (
