Recovery phase of ATN

[Derivations]

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UWorld (QID 886) states that during the recovery phase of acute tubular necrosis you get low serum levels of K, Mg, PO4, and Ca due to high volume hypotonic urine.

Wouldn't hypotonic urine lead to high values of these electrolytes in the blood? I must be missing something but right now it isn't making sense to me.

Thanks in advance.

 

[GomerPyle]

I initially had the same confusion as you. Yes, in the recovery phase you have increased secretion of K, Mg, PO4, and Calcium but you are peeing out 3 liters of fluid per day which dilutes the urine so much that it's hypotonic even though you have increased solute excretion.

 

[amberkre]

I kind of think about the last phase of ATN like a loop diuretic. Since the tubular epithelium has regenerated and the patient is urinating high volumes of dilute urine its basically like the effect of giving a loop. The patient will have increased secretion of K+ = hypokalemia and they will also have increased losses of Ca+. Idk if this is an oversimplification but it has worked for me on questions.