Clinical Lab Handbook

Specimen: SST

Alternate Container: Light Green (Lithium Heparin), Red top

Specimen Volume: 3 mL

Collections Instructions: Spin down immediately.

Centrifuge specimens and remove the serum or plasma from the cellular material within 2 days of collection.

Potentiometric, Ion-Selective Electrode (ISE)

The VITROS Na+ Slide is a multilayered, analytical element coated on a polyester support that uses direct potentiometry 2 for measurement of sodium ions. The slide consists of two ion-selective electrodes, each containing methyl monensin (an ionophore for sodium), a reference layer, and a silver layer and a silver chloride layer coated on a polyester support.

A drop of patient sample and a drop of VITROS Electrolyte Reference Fluid on separate halves of the slide results in migration of both fluids toward the center of the paper bridge. A stable liquid junction is formed that connects the reference electrode to the sample electrode.

Each electrode produces an electrochemical potential in response to the activity of sodium. The potential difference between the two electrodes is proportional to the sodium concentration in the sample.

Sodium is the major cation of extracellular fluids. The kidneys regulate sodium content of the body. Low sodium levels may be caused by excessive urine loss, diarrhea, Addison’s disease, and renal tubular disease. High sodium levels may occur in severe dehydration, some types of brain injury, diabetic coma, and excessive intake of sodium salts.

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