Which of the following is NOT a selenium status indicator?

• A. Plasma glutathione peroxidase
• B. Selenium level in whole blood
• C. Plasma selenium
• D. Methionine

Answer: (D)

Assessing selenium status relies on both how much selenium is circulating or stored in the body and how well selenium-dependent enzymes are functioning. Plasma glutathione peroxidase activity reflects functional selenium status because glutathione peroxidase is a selenoprotein that requires adequate selenium to be active; its activity decreases when selenium is limited, signaling impaired selenoprotein synthesis. Measuring selenium in whole blood provides a longer-term view of body stores and intake, since blood levels correlate with tissue selenium over time. Plasma selenium concentration is another common biomarker, indicating the circulating pool available for utilization and incorporation into selenoproteins. Methionine, while an essential amino acid, does not indicate selenium status and has no direct, specific link to selenium stores or selenoprotein activity.