Sodium In Body Fluid

More Specific Terms

The Kodak Ektachem Clinical Chemistry Slide (Na+) is a dry, multilayered, analytical element that uses direct potentiometry for measurement of sodium ions. The slide consists of two ion- selective electrodes, each containing methyl monensin (an ionophore for sodium), a reference layer, & a silver & silver chloride layer coated on a plastic support.
Application of 10 uL of patient sample & 10 uL of the Kodak Ektachem Electrolyte Reference Fluid to separate halves of the slide results in migration of both fluids towards the center of the paper bridge. A stable liquid junction is formed connecting the reference electrode to the sample indicator electrode.
Each electrode produces an electrical potential in response to the activity of sodium applied to it. The potential difference poised between the two half electrodes is proportional to the sodium concentration in the sample.

Sodium is the primary extracellular cation. The amount of sodium in the body is a reflection of the balance between sodium intake & output. Sodium assays are important in assessing acid-base balance, water balance, water intoxication, & dehydration.
Sodium is freely filtered by the glomerulus, & the major route of sodium excretion is through the kidneys. Measurement of urinary sodium is used to determine volume depletion, acute renal failure, salt-losing nephritis, & in the differential diagnosis of hyponatremia.

No special patient preparation is required.
For serum preparation: collect whole blood & allow to clot according to manufacturer's instructions. Specimens are collected in a red top vacutainer by venipuncture & should be separated immediately from the cells after collection.
Heparin may be used as an anticoagulant for plasma specimens, although sodium heparin will increase the measured sodium value by approximately 0.5 mmol/L. Do not use potassium oxalate/ sodium fluoride anticoagulants.
Urine: Collect timed or random specimens by standard laboratory procedures. Preservatives are not necessary & may interfere. Refrigerate specimen during collection & keep refrigerated until analysis.
Preparation (Urine)

Remove Kodak Ektachem Urine Electrolyte Diluent from the refrigerator & allow to reach room temperature (45 minutes).
Mix the diluent by gently swirling & inverting the container. DO NOT SHAKE.
In a clean, dry container, accurately dilute one part sample with four parts urine diluent (fivefold dilution). Immed- iately cover diluent & return it to refrigerated storage.
Thoroughly mix sample with diluent.
Analyze the diluted sample & multiply the reported result by 5 to obtain the sodium concentration in the original sample.

Minimum sample size 0.5 milliliter: with an optimum size of 1.0 milliliters or larger.

Preliminary data indicated that hemolysis, icterus & lipemia do not interfere with this method.
Ethanol levels at 150 mg/dL causes an increase of 2 mmol/L in reported results.
Specimens contaminated with cationic surfactants show a positive interference (e.g. benzalkonium chloride at 10 mg/L caused a 50 mmol/L apparent increase in sodium.

Kodak Ektachem 700 Analyzer Operator's Manual, Kodak Clinical Products, Rochester, New York.
Kodak Ektachem Clinical Slide Package Insert, Kodak Clinical Products, Rochester, New York.
Kodak Ektachem Clinical Training Manual, Kodak Clinical Products, Rochester, New York.
Tietz, N. W.: Electrolytes, in Textbook of Clinical Chemistry, Philadelphia, W. B. Saunders Co., p. 1845, 1986.

sodium (Na+) in serum & urine