Talk:Fractional excretion of sodium

Untitled
I'm just learning those concept so I may be wrong...

In this article, the mathematical equation seems right, but I don't see how to relate the two "other" way of computing FE (that are discuss in text just before the equation). The fractional excretion value are a percentage (no unit) but the two suggested way have units :

(1) "FENa can be calculated by multiplying the plasma sodium concentration by the glomerular filtration rate"

GFR (ml/min) X [Na]plasma (mmol/ml) = mmol/min

(2) "It may also be calculated by multiplying the urine sodium concentration by the urinary flow rate"

[Na]urine (mmol/ml) X Vurine (ml/min) = mmol/min

Could you explain more in detailled how those way of computing the FE are good ? is there an approximation somewhere that is not discuss ?

thank you

Let me explain what FeNa really is and how it should be used: What is often left behind is that FeNa is the ratio between Na clearance and creatinine clearance. How's that? (1) Na clearance = (Urine [Na]/Serum [Na]) x urine flow (ml/min) (2) Creatinine clearance = (Urine [creatinine]/Serum [creatinine]) x (3) Na clearance/creatinine clearance = (Urine [Na] x Serum [creatinine])/(Serum [Na] x Urine [creatinine]) x urine flow (ml/min)/urine flow (ml/min) Notice that urine flow is canceled out (reason why knowing urine flow is not needed), and then it is multiplied by 100 to express it as a percentage; which is odd reporting a fraction as a percentage but that's the way we are accustomed to. What does it really mean? If the kidney is doing what it is supposed to do, it will excrete creatinine (an end-product "waste" of metabolism) and if -- only if -- there is a signal to retain fluid (e.g., intravascular volume deficit, a low flow state, etc) it will reduce Na clearance and lead to a low FeNa. In other words, the measuring FeNa has meaning only when used for the differential diagnosis of oliguria. In a way it is like a stress test for the kidney. If the kidney is working normally and is able to preserve its function when there is a reduction in renal blood flow, it will preserve its ability to excrete creatinine while retaining Na in response to a reduction in renal blood flow intended to expand the intravascular volume.

Raúl J. Gazmuri MD, PhD, FCCM Director, Resuscitation Institute Professor of Medicine and Professor of Physiology & Biophysics Rosalind Franklin University of Medicine and Science Section Chief, Critical Care and ICU Director Captain James A. Lovell Federal Health Care Center raul.gazmuri@rosalindfranklin.edu

to add in the future.
Use something like what they have for BMI changing the wording of course.

24.43.8.159 (talk) 04:16, 16 March 2009 (UTC)

Why not urine concentration alone
This is incorrect: "It is measured in terms of plasma and urine sodium, rather than by the interpretation of urinary sodium concentration alone, as urinary sodium concentrations can vary with water reabsorption"

To fix the fact that urinary concentrations vary with water reabsoption, you need to get urinary flow. Plasma concentration has nothing to do with adjusting for this variation. —Preceding unsigned comment added by 87.194.220.146 (talk) 15:03, 21 April 2011 (UTC)

I am completely new to this subject and felt that the article assumes that the reader has a medical backgound and that some elaboration would help the lay reader.

From the article I inferred that sodium excretion in the kidney is a two stage process, glomerular filtration followed by reabsorbtion. The fractional excretion rate is a measure of the effectiveness of the reabsorbion stage. The glomerular filtration rate is assumed to be the same for sodium as for creatinine. I would have liked to see some justification for this assumption. There is also an assumption that there is no reabsorbtion of creatinine. Given these assumptions the rest follows fairly clearly. The interpretation section then implies that virtually all sodium should be reabsorbed, anything less than 99 percent of sodium being reabsorbed implies a pathological condition. However, the first section refers to a stimulus to conserve sodium, which suggests that there might be situations in which a higher FENa might be desirable.

Finally, some actual figures would be helpful, as they might make it possible to relate the article to actual sodium intake, although there are presumably other mechanisms for sodium excretion. Sweating comes to mind.

The table given at the start of the article is completely useless, as the figures are given without units (this should never happen, EVER.) and the abbreviations are not explained. Chrisbaarry (talk) 06:56, 5 October 2011 (UTC)