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The fractional excretion of sodium (FE Na) is the percentage of the sodium filtered by the kidney which is excreted in the urine. 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 .
Urine electrolyte levels can be measured in a medical laboratory for diagnostic purposes. The urine concentrations of sodium , chlorine and potassium may be used to investigate conditions such as abnormal blood electrolyte levels, acute kidney injury , metabolic alkalosis and hypovolemia .
The urine sodium is expressed as a concentration (such as millimoles per liter). The result must therefore be interpreted in the context of the degree of urine concentration present. Alternatively, the urine sodium can be standardized to the excretion of creatinine using a formula such as the fractional excretion of sodium (FENa).
It uses Na-H antiport, Na-glucose symport, sodium ion channels (minor). [1] It is stimulated by angiotensin II and aldosterone, and inhibited by atrial natriuretic peptide. It is very efficient, since more than 25,000 mmol/day of sodium is filtered into the nephron, but only ~100 mmol/day, or less than 0.4% remains in the final urine.
Creatinine clearance exceeds GFR due to creatinine secretion, [4] which can be blocked by cimetidine. Both GFR and C Cr may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result ( eGFR and eC Cr ) The results of these tests are used to assess the ...
Example of a container used for collecting 24-hour urine samples. This particular container is free of trace metals to allow for accurate measurement of these substances in urine. The techniques used to collect urine specimens vary based on the desired test. A random urine, meaning a specimen that is collected at any time, can be used for many ...
Two other urinary indices, are the fractional sodium excretion (FENa) index and the renal failure index (RFI). [36] The renal failure index is equal to urine sodium times plasma creatinine divided by urine creatinine. [36] A FENa score greater than 3% or a renal failure index (RFI) greater than 3 are helpful in confirming acute renal failure. [37]
If proteinuria is persistently detected by dipstick testing, a 24-hour urine collection can be performed to obtain an accurate measurement of protein levels; alternatively, protein excretion can be estimated from the urine protein/creatinine ratio of a single specimen. Measuring the amount of protein in the urine helps to distinguish between ...