Ans. a (Renal tubular acidosis). (Ref. Harrison's Medicine 16th/pg. 265, 1702)METABOLIC ACIDOSIS: There are two major categories of clinical metabolic acidosis:# High anion-gap (AG) and# Normal-AG, or hyperchloremic acidosis:Hyperchloremic (nongap) metabolic acidosis# Alkali can be lost from the gastrointestinal tract in diarrhea or from the kidneys (renal tubular acidosis, RTA). In these disorders, reciprocal changes in and result in a normal AG.# In pure hyperchloremic acidosis, therefore, the increase in above the normal value approximates the decrease in . The absence of such a relationship suggests a mixed disturbance.# Metabolic acidosis due to gastrointestinal losses with a high urine pH can be differentiated from RTA because urinary NH4 excretion is typically low in RTA and high with diarrhea.# Urinary NH4 -levels can be estimated by calculating the urine anion gap (UAG):- UAG = -.# When > , and the urine gap is negative, the urine ammonium level is appropriately increased, suggesting an extrarenal cause of the acidosis.# Conversely, when the urine anion gap is positive, urine ammonium level is low, sugg. renal acidosis.The typical findings in classic distal RTA (type 1 RTA) include:# Hypokalemia,# Hyperchloremic acidosis,# Low urinary NH4"# Excretion (positive uag, low urine [NH4U, and# Inappropriately high urine pH (pH -5.5).# Most have hypocitraturia and hypercalciuria, so nephrolithiasis, nephrocalcinosis, bone ds common.# Proximal RTA (type 2 RTA) is most often due to generalized proximal tubular dysfunction manifested by glycosuria, generalized aminoaciduria, and phosphaturia (Fanconi syndrome).# In type 4 RTA, hyperkalemia is disproportionate to the reduction in GFR because of coexisting dysfunction of potassium and acid secretion.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/kgVariableTable: COMPARISON OF NORMAL ANION-GAP ACIDOSISAlso remember:FUNCTIONAL CONSEQUENCES OF TUBULOINTERSTITIAL DISEASEDefectCause(s)1Reduced GFRObliteration of microvasculature and obstruction of tubules2Fanconi syndromeDamage to proximal tubular reabsorption of glucose, amino acids, phosphate, and bicarbonate3Hyperchloremic acidosis1. Reduced ammonia production2. Inability to acidify the collecting duct fluid (distal renal tubular acidosis).3. Proximal bicarbonate wasting4Tubular/small-molecular weight proteinuriaFailure of proximal tubule protein reabsorption5Polyuria, isothenuriaDamage to medullary tubules and vasculature6HyperkalemiaPotassium secretory defects including aldosterone resistance7Salt wastingDistal tubular damage with impaired sodium reabsorptionPRIMARY HYPERALDOSTERONISM (Conn's syndrome)# Conn's adenoma is very sensitive to ACTH as is glucocorticoid suppressible hyperaldosteronism, hence morning levels of ACTH and aldosterone are low.# Idiopathic bilateral adrenal hyperplasia is common than adrenal adenoma,# K+ levels are normal in 70% cases.# Increased plasma and urinary aldosterone.# Decreased plasma renin activity.6# Its dexamethasone suppressive hyperaldosteronism.# 18 OH cortisol levels are very high in Conn's adenoma and glucocorticoid suppressible hyperplasia.# Spironolactone is drug of choice.Secondary hyperaldosteronism results from:# Nephritic syndrome,# Cirrhosis,# Heart failure and# Barter's syndrome.'Spirolactone bodies' are seen in ATCH secreting adrenal adenomas treated with Spironolactone.