Renal Tubular Acidosis
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Renal Tubular Acidosis Arvind Bagga 1
&
Aditi Sinha 1
Received: 14 April 2020 / Accepted: 21 April 2020 # Dr. K C Chaudhuri Foundation 2020
Abstract Renal tubular acidosis (RTA) comprises a group of disorders characterized by low capacity for net acid excretion and persistent hyperchloremic metabolic acidosis, despite preserved glomerular filtration rate. RTA are classified into chiefly three types (1, 2 and 4) based on pathophysiology and clinical and laboratory characteristics. Most patients have primary RTA that presents in infancy with polyuria, growth retardation, rickets and/or hypotonia. Diagnosis requires careful evaluation, including exclusion of other entities that can cause acidosis. A variety of tests, administered stepwise, are useful for the diagnosis and characterization of RTA. A genetic or acquired basis can be determined in majority of patients through focused evaluation. Management involves correction of acidosis and dyselectrolytemia; patients with proximal RTA with Fanconi syndrome and rickets require additional supplements of phosphate and vitamin D. Keywords Metabolic acidosis . Fanconi syndrome . Anion gap
Introduction Renal tubular acidosis (RTA) is a group of transport defects characterized by reduced proximal tubular reabsorption of bicarbonate (HCO3−), distal secretion of protons (hydrogen ion, H+) or both, resulting in impaired capacity for net acid excretion, and persistent hyperchloremic metabolic acidosis, in presence of normal glomerular filtration rate. Based on pathophysiology, three major types of RTA are recognized [1]. The authors discuss the pathophysiological and inherited bases, clinical features, and principles of diagnosis and management of the disorder.
Physiology The human body generates approximately 1 mEq/kg of net acid (H+) daily. Proximal tubules reabsorb 85–90% (~4000– 4500 mEq/d) of filtered bicarbonate (HCO3−) (Fig. 1a) [1–3]. The proximal convoluted tubule (PCT) also reabsorbs ~60% of filtered sodium (Na+) along with water, potassium (K+), glucose, phosphate, amino acids and low molecular weight * Arvind Bagga [email protected] 1
Division of Nephrology, Department of Pediatrics, All India Institute of Medical Sciences, New Delhi 110029, India
proteins (Fig. 1a). The remaining bicarbonate is absorbed in the thick ascending limb (TAL) of loop of Henle and βintercalated cells of collecting ducts (CD). The distal convoluted tubule (DCT) and CD have a specialized role in the final modification of urine concentration and pH, through specific transporters that mediate K+ and H+ secretion by α-intercalated cells and Na+ reabsorption by principal cells (Fig. 1b and c) (4, 5). Free H+ contributes a small fraction to net acid excretion. Ammoniagenesis in the proximal tubules, followed by its conversion to ammonium (NH4+) distally, is an important mechanism of H+excretion [6]. Another mode of H+ excretion is as titratable acidity, chiefly as H2PO4− [7]. At lower urinary pH, creatinine, and in ketoacidosis, β-hydroxybutyrate also contribute to ti
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