Table 5.

Differential diagnosis of various types of RTAa

Proximal RTA (type 2)Distal RTA (type 1)Hyperkalemic RTA (type 4)
“Classic”With HCO3 Wasting (type 3)Hyperkalemic
a N, normal; I, increased; D, decreased.
In situation of metabolic acidosis (spontaneously or after acid loading)
    plasma K+N or DN or DN or DII
    urinary anion gapNegativePositivePositivePositivePositive
    urine pH<5.5>5.5>5.5>5.5<5.5
    NH4+ excretionNDDDD
    fractional K+ excretionN or IIIDD
    Ca excretionNIIIN or D
    citrate excretionNDDDN
In situation of normal acid-base equilibrium (after alkali loading)
    fractional HCO3 excretion>10 to 15%<5%>5 to 15%<5%>5 to 10%
    U-B Pco2>20 mmHg<20 mmHg<20 mmHg>20 mmHg>20 mmHg
Other tubular defectsOften presentAbsentAbsentAbsentAbsent
Nephrocalcinosis/lithiasisAbsentOften presentOften presentOften presentAbsent
Bone involvementOften presentRarely presentRarely presentRarely presentAbsent