Diuretics: electrolyte changes

Question 1

Urine NaCl

Answer 1

All diuretics increase

Serum NaCl may decrease as a result

Question 2

Urine K+

Answer 2

All increase except for K+ sparing.

Serum K+ may decrease as a result

Question 3

Blood pH: acidemia

Answer 3

Carbonic anhydrase inhibitor: low bicarb reabsorption
K+ sparing: block K+ and H+ secretion

Additionally, hyperkalemia leads to K+ entering all cells (via H+/K+ exchanger) in exchange for H+ exiting cell

Question 4

Blood pH: alkalemia

Answer 4

Loop diuretics and thiazides:

1) volume contraction -> ATII increase -> increase Na+/H+ exchange in the proximal tubule -> increase bicarb reabsorption (“contraction alkalosis”)
2) K+ loss leads to K+ exiting all cells (via H+/K+ exchanger) in exchange for H+ entering cells
3) in low K+ state, H+ (rather than K+) is exchanged for Na+ in cortical collecting tubule, leading to alkalosis and “paraxodical aciduria”

Question 5

Urine Ca2+

Answer 5

Increase with loop diuretics: low paracellular Ca2+ reabsorption, so hypocalcemia

Decrease with thiazide: enhanced paracellular Ca2+ reabsorption in proximal tubule and loop of henle.