<prompt> Which of the following is characteristic of RTA- type 1?Hyperkalemia.Decreased NH4 excretionAcidosis with normal chlorideNone  <response>: Ans. b Decreased NH4 excretion Ref. Harrison 18th ch. 285RENAL TUBULAR ACIDOSIS RTA RTA is a disorder of renal acidification out of proportion to the reduction in glomerular filtration rate. RTA is featured by hyperchloremic metabolic acidosis with normal serum anion gap . There are multiple forms of RTA, depending on which aspects of renal acid handling have been affected. Defective bicarbonate reabsorption in the proximal tubule, suppressed renal ammoniagenesis, and inadequate distal tubule proton secretion are the abnormalities that produce RTA. Three major forms of RTA exist:Types 1 and 2 may be inherited or acquired.- Type 4 is usually acquired and is associated with either hypoaldosteronism or tubular hyporesponsiveness to mineralocorticoids.- Type 3 is a very rare form of RTA with features of both type 1 and type 2 RTA. It is due to deficiency of carbonic anhydrase II, an enzyme present in both the proximal and distal tubules. It is an autosomal recessive disease associated with osteopetrosis and mental retardation.FindingType 1 RTAType 2 RTAType 4 RTAGI Bicarbonate lossNormal anion-gap acidosisYesYesYesYesMinimum urine pH5.55.55.55 to 6 Filtered bicarbonate excreted10151010Serum potassiumLowLowHighLowFanconi syndromeNoYesNoNoStonesnephrocalcinosisYesNoNoNoDaily acid excretionLowNormalLowHighUrine anion gapPositiveNegativePositiveNegativeDaily bicarbonate replacement needs 4 mmolkg 4 mmolkg 4 mmolkgVariable 