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Author Topic: Evaluating metabolic alkalosis using urinary studies
Tejas
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Posts: 37
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Post Evaluating metabolic alkalosis using urinary studies
on: October 19, 2013, 12:38
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I have a ? 4 you. Why do we check urine cl- in low k+ and metabolic alkalosis and not urine k+?

Tejas
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Posts: 37
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Post Re: Evaluating metabolic alkalosis using urinary studies
on: October 19, 2013, 12:46
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Re: Checking urinary Cl- in metabolic alkalosis:

One of the functions of Cl- is to accompany Na+ during its reasborption by the kidney. Cl- is the most abundant anion and makes a good partner when the kidney wants to reabsorb Na+. The 2nd most abundant anion, HCO3-, can also accompany Na+, but is generally not used for this purpose unless Cl- is in short supply.

In a metabolic alkalosis, there is always the possibility the high serum HCO3- is due to excessive reabsorption (along with Na+) by the kidney. This would occur because of a low amount of Cl-. Therefore, checking the urinary Cl- excretion would tip you off to low amounts of Cl-. Low urinary Cl- concentrations in the setting of a high serum bicarbonate would suggest this mechanism. The treatment would be to simply restore the Cl- levels in the body, with either NaCl (salt tabs, saline), or KCl.

Re: Checking urinary K+ levels:

We generally do not check spot urinary K+ levels (unlike other spot urine levels). Spot urinary K+ levels are not a good reflection of the amount of K+ that is being excreted. The reason for this is the location in which K+ is secreted -- the distal tubule. H2O enters the urinary space near the distal tubule, and thus can alter the urine K+ concentration. Since H2O and K+ secretion are not directly related to one another (unlike H2O and Na+ secretion), you could be fooled into thinking that a low urine K+ signifies low excretion of K+.

We have a short 10-Minute Rounds video about this here.

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