Thursday, 19 January 2012
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The best way to assessment of Dietery Salt restriction is 24 h urinary sodium, right. The question is In CKD, CHF, Nephrosis, and cirrhosis states are very salt avid, the kidneys reabsorb >99% of the filtered load of sodium. How does the salt intake correlate with the salt loss giving the fact not all patients are in steady state? Please explain. Mohammad Samih, MD, MACP Nephrologist, Harlan ARH Hospital
Accepted Answer
Hr. Samih,

By definition, in steady state, the kidney will excrete what one eats. Yes, the kidney reabsorbs 99% of filtered sodium but that amounts to roughly 20,000 mmol per day filtered and only, say 100-200 excreted (depending on what one eats). A 24 hour urine is the gold standard for measuring sodium intake. I think it is superior to an estimate using spot urine sodium to creatinine ratio because one's sodium intake would not be constant throughout the day.
Accepted Answer
Hr. Samih,

By definition, in steady state, the kidney will excrete what one eats. Yes, the kidney reabsorbs 99% of filtered sodium but that amounts to roughly 20,000 mmol per day filtered and only, say 100-200 excreted (depending on what one eats). A 24 hour urine is the gold standard for measuring sodium intake. I think it is superior to an estimate using spot urine sodium to creatinine ratio because one's sodium intake would not be constant throughout the day.
9 years ago
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#109
What if the patient is not in steady state?
If the intake is equal to the output, and your kidneys lose whatever you take, whay do we restrict salt intake?
If the patient is not in steady state, the 24 hr urine is not valid.
Your question about salt restriction is an excellent one. It's controversial (despite what nutritional authorities say) that salt restriction is important for blood pressure reduction. In fact, there is little prospective data that it matters for the general population. However, if one eats salt on a daily basis they will likely be maintained at a slightly volume expanded steady state, contributing possibly to hypertension and then every subsequent day they excrete what they eat. So you're correct, they must have retained some sodium or else they would never become volume expanded. But if they did not excrete what they ate thereafter, they would become progressively more edematous with each passing day and we know this does not happen in general.
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