Which of the following is characteristic of RTA- type 1?
Correct Answer: Decreased NH4+ excretion
Description: Ans. b (Decreased NH4+ excretion) (Ref. Harrison 18th/ ch. 285)RENAL 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 pH>5.5<5.5<5.55 to 6% Filtered bicarbonate excreted<10<15<10<10Serum potassiumLowLowHighLowFanconi syndromeNoYesNoNoStones/nephrocalcinosisYesNoNoNoDaily acid excretionLowNormalLowHighUrine anion gapPositiveNegativePositiveNegativeDaily bicarbonate replacement needs< 4 mmol/kg> 4 mmol/kg< 4 mmol/kgVariable
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