Electrolyte imbalances are difficult to detect simply. Careful homeostatic control by both hormones and kidney function, cover up disorders that effect electrolytes therefore simple serun or plasma concentration in the blood cannot be used to detect abnormalites of dietary intake, kidney disease, or hormonal dysfunction. Fractional excretion test is a practical means of assessing alterations in electrolyte status and kidney function. Possible indications include:

• Performance problems
• Suspected kidney disease
• Recurrent rhabdomyolysis (Tying Up)
• Evaluating nutritional status of electrolytes

Creatinine is excreted by the kidneys at a rate fairly consistent with that of the filtration rate of the kidney (GFR). On the other hand electrolytes are conserved in the tubules by resorption which depends on the integrity of the kidneys. Therefore creatinine excretion can be used as a standard which to compare the function of the kidneys tublules and/or whether the body is conserving or trying to get rid of electrolytes. Low dietary intake of a electrolyte results in its conservation by the kidney and a low FE value and conversely high dietary intake elevates the fractional excretion rate. On the other hand kidney disease and dysfunction will raise the fractional excretion rate of all electrolytes.