In a grossly lipemic sample, which method yields the most accurate electrolyte results?

In a grossly lipemic sample, which method yields the most accurate electrolyte results?

• A. Direct ISE
• B. Indirect ISE
• C. Flame emission photometry
• D. Atomic absorption

Answer: (A)

Gross lipemia leaves less aqueous plasma for ions to reside in, which creates problems for methods that rely on the sample’s water content. Indirect ion-selective electrode measurements require diluting the sample and assume a constant water fraction; in a lipemic sample, the lipid portion gets included in the dilution, making electrolyte readings falsely low—a phenomenon known as pseudohyponatremia for sodium, and similar biases can occur for other electrolytes. Direct ion-selective electrode analysis, on the other hand, tests the undiluted sample and measures ion activity directly in the aqueous phase, so the lipid content has much less impact and the results are more accurate in lipemic specimens. The other techniques listed aren’t designed for routine electrolyte measurement in this context and don’t compensate for lipemia the way direct ISE does.

Gross lipemia leaves less aqueous plasma for ions to reside in, which creates problems for methods that rely on the sample’s water content. Indirect ion-selective electrode measurements require diluting the sample and assume a constant water fraction; in a lipemic sample, the lipid portion gets included in the dilution, making electrolyte readings falsely low—a phenomenon known as pseudohyponatremia for sodium, and similar biases can occur for other electrolytes. Direct ion-selective electrode analysis, on the other hand, tests the undiluted sample and measures ion activity directly in the aqueous phase, so the lipid content has much less impact and the results are more accurate in lipemic specimens. The other techniques listed aren’t designed for routine electrolyte measurement in this context and don’t compensate for lipemia the way direct ISE does.