1. RENAL TUBULAR
ACIDOSIS

2.  First described clinically in  Refers to disorders
1935 affecting the overall ability
 Confirmed as a renal of the renal tubules either
tubular disorder in 1946 to secrete hydrogen
 Designated as RTA in 1951 ions or to retain
bicarbonate ions
 All types produce
hyperchloremic metabolic
acidosis
with a normal anion gap.

3. PROXIMAL RENAL TUBULAR
ACIDOSIS
 MAIN DEFECT
 Carbonic Anhydrase deficiency

4. Proximal RTA (Type 2)
 Caused by an
impairment of HCO3-
reabsorption in the
proximal tubules
 Most cases occur in
the context of
Fanconi’s syndrome
 Isolated proximal RTA
is rare.

5. HCO3
100%
HCO3
HCO3
80% reabsorbed 15% reabsorbed
HCO3
5% excreted
Normal renal tubular function

6. HCO3
100% HCO
3
HCO3
60% reabsorbed 15% reabsorbed
Decreased proximal tubule
efficiency Cl-
25% HCO3-
K+
Proximal RTA or RTA type 2

7. Proximal RTA
 Massive loss of bicarbonate – metabolic acidosis
 Absorption of chloride - hyperchloremia
 Loss of potassium – hypokalemia
 Kidneys tries to compensate for the acidosis –
urine ph is low - < 5.5

8. Distal RTA
 Decreased excretion of titratable acids =
Acidification defect

9. DISTAL RTA
 Impairment of distal
acidification
 Inability to lower urine pH
maximally below 6.0 under
acid load
 Pathomechanism is inability
to secrete H+ adequately
(secretory defect or classic
distal RTA)
 Gradient defect
 Voltage dependent defect
 In children mainly a genetic
defect of the H+ pump

10. Cl-
Distal RTA
or RTA type 1
Acidification defect
H+
HCO3-
K+
excreted

11. Distal RTA
 Loss of bicarbonate less than type 2 – metabolic
acidosis
 Absorption of chloride – hyperchloremia
 Loss of potassium – hypokalemia
 Decreased excretion of titratable acids – high
urinary ph >5.5

12. RTA Type IV
 Hypoaldosteronism or Deficiency of aldosterone
 Pseudohypoaldosteronism or end organ target
failure

13. Na
Adolsterone H20
RTA IV: K+
Cl-
Hypoaldosteronism or
pseudohypoaldosteronism H+
Water
Na+

14. RTA IV
 End organ target failure or low aldosterone:
 Lost of sodium – hyponatremia
 Retention or decreased excretion of potassium -
hyperkalemia
 Absorption of chloride – hyperchloremia
 Decreased excretion of acids – metabolic
acidosis
 Loss of fluid - dehydration

15. Proximal RTA Distal RTA RTA IV
Type of Hyperchloremic Hyperchloremic Hyperchloremic
Acidosis metabolic metabolic metabolic
acidosis acidosis acidosis
Serum low low high
Potassium
Urine pH < 5.5 >5.5 < 5.5
Urine
bicarbonate
loss

16. Features of the RTA Syndromes
Feature Type 1 Type 2 Type 4
Nephro- present absent Absent
lithiasis
Nephro- present absent Absent
calcinosis
Osteo- present present Absent
malacia
Growth +++ ++ +++
failure
Hypokalemic ++ + -
muscle
weakness
Alkali Low dose (2 High dose ( Low dose ( 2-
therapy –4 meq/kg) 2-14 meq/kg) 3 meq/kg)
Response to good fair fair
therapy

17. Features of the RTA Syndromes
Feature Type 1 Type 2 Type IV
Plasma HCO3 Variable, 14- 18 meq/L 15-29 meq/L
may be <10
meq/L
Plasma Cl- increased Increased Increased
Plasma K+ Mildly to Mildly Mildly to
severely decreased severely
decreased decreased
Plasma anion Normal Normal Normal
gap
GFR Normal or Normal of Normal to
slightly slightly moderately
decreased decreased decreased
Fractional <5% > 15% <5%
Excretion of
HCO3
Urine pH >6.0 </= 5.5 </= 5.5
during
acidosis