C Appendix 3 - what’s the mechanism?

C.1 Mechanisms in dRTA (see ESPN clinical practice points, NDT 2021):

Mechanism of hypoK in dRTA:

1. response to systemic acidosis (inhibits PCT Na reabsorption and therefore stimulates RAAS)
   
2. increased voltage gradient in CD (Na reabsorption not balanced by H excretion)
   
3. sometimes also drug-induced direct causes (e.g. amphoterocin)

Mechanism of hypoK in pRTA:

1. increased HCO3 delivery and flow rate in distal nephron (Unwin 2001)

Mechanism of hypercalciuria in dRTA:

1. release of Ca from bone (as protons are buffered by apatite)
   
2. tubular resistance to the anti-calicuric effects of PTH

Mechanisms of stones / nephrocalcinosis in dRTA:

1. hypercalciuria
   
2. hypocituria (enhanced reabsorption of citrate in PCT; citrate inhibits stone formation)