Snapshot A 7-year-old boy presents to his pediatrician for a wellness visit. The mother reports that the patient urinates frequently and does not appear to be as tall as his classmates. Upon further questioning, the patient's mother states he has episodes of constipation and muscle weakness. Physical examination is notable for growth failure. Laboratory testing is significant for hyperchloremic metabolic acidosis, hypophosphatemia, and hypokalemia. Urinalysis is notable for a urine pH < 5.5, aminoaciduria, and glucosuria. (Fanconi syndrome leading to a type II renal tubular acidosis.) Introduction Clinical definition renal tubular dysfunction that results in a hyperchloremic and normal anion gap metabolic acidosis there is a relatively normal glomerular filtration rate Renal Tubular AcidosisTypeEtiologyPathogenesisTreatmentCommentsType II (proximal)Fanconi syndromeCarbonic anhydrase II deficiencyMedicationsacetazolamideifosfamidetopiramateHeavy metalse.g., mercury, cadmium, copper, and leadMultiple myelomaWilson disease↓ bicarbonate reabsorption in the proximal tubuleadminister bicarbonate and urine remains basicPotassium citrateThiazide diureticsAssociated with hypokalemiaAt risk of developing hypophosphatemic ricketsUrine pH is initially > 5.5 and then later becomes < 5.5Type I (distal)Sjogren syndromeRheumatoid arthritisAnion exchanger gene mutationsMedicationslithiumifosfamideanalgesicsamphotericin BDefective hydrogen secretionSodium bicarbonate or sodium citrateAssociated with hypokalemiaAt risk of developing calcium phosphate stonesUrine pH > 5.5Type IV (hyporeninemic hypoaldosteronism)Diabetic nephropathyMineralocorticoid deficiencySickle cell diseaseSystemic lupus erythematosusMedicationsheparinangiotensin converting enzyme (ACE) inhibitorsangiogensin receptor blockers (ARBs)cyclosporineTMP-SMXpotassium sparing diureticsHyperkalemia results in ↓ ammonia (NH3) synthesis↓ the capacity to carry acidTreatment depends on the underlying causeAssociated with hyperkalemiaUrine pH < 5.5