Which statement is true about direct ISE method?

Which statement is true about direct ISE method?

• A. Whole blood specimens are acceptable
• B. Elevated lipids cause falsely increased results
• C. Elevated proteins cause falsely increased results
• D. Elevated platelets cause falsely decreased results

Answer: (A)

Direct ISE analyzes electrolytes in an undiluted sample, so it can be used with whole blood. Because there is no dilution step, the measurement reflects ion activity in the plasma water fraction of the sample, and whole blood is suitable for this method. Elevated lipids or elevated proteins distort results in the diluted indirect method by changing the plasma water fraction (pseudohyponatremia), not in the direct method. Elevated platelets aren’t a recognized cause of a false decrease in direct ISE readings, so those statements don’t apply here.

Direct ISE analyzes electrolytes in an undiluted sample, so it can be used with whole blood. Because there is no dilution step, the measurement reflects ion activity in the plasma water fraction of the sample, and whole blood is suitable for this method.

Elevated lipids or elevated proteins distort results in the diluted indirect method by changing the plasma water fraction (pseudohyponatremia), not in the direct method. Elevated platelets aren’t a recognized cause of a false decrease in direct ISE readings, so those statements don’t apply here.