WHAT IS SODIUM (PLASMA) TEST?
Sodium is the major cation of extracellular fluid. Its primary function is to maintain osmotic pressures and acid-base balance and to transmit nerve impulses. It is absorbed from the small intestine and excreted in the urine in amounts dependent on dietary intake. In normal clients, the sodium content of the body remains fairly constant despite wide variations in sodium intake.
Urinary sodium levels are used in conjunction with urine and plasma or serum creatinine levels in two formulas that help narrow down the source of renal failure into prerenal, renal, and postrenal causes. See Renal indices— Diagnostic for further explanation of the use of these formulas.