Selenium
Serum and Plasma Selenium
Serum and plasma selenium responds to short-term changes in diet and measuring
the amounts of selenium in serum and plasma can indicate short-term selenium
status. Normal selenium levels of the U.S. population fall within the range of
2.03-3.29 micromoles (mcmol) per liter (L).
Whole-Blood Selenium
Selenium levels in whole blood do not fluctuate much and are thus more
indicative of long-term selenium status. A new technique that can be used to
analyze serum, plasma or whole blood selenium is called graphite furnace atomic
absorption spectrometry. This method is fairly easy to execute and the
resultant samples require little pretreatment.
Urinary Excretion
Urine samples reflect selenium content of the previous meal and are not useful
for assessment of selenium status, though they can be used to detect toxicity.
Toenail Selenium
Toenail selenium is useful for assessment of long-term selenium status.
Selenium is incorporated into toenails as they grow. Because the exposed
toenail on which tests are done have long since ceased to grow, toenail selenium
levels probably reflect zinc status as it stood six to nine months prior to
testing.
Glutathione Peroxidase Activity
There is a correlation between blood glutathione peroxidase activity and
blood selenium up to 1.2 mcmol/L. Beyond that point the activity plateaus, and
cannot be used to determine selenium status. The test is not specific because
other factors can affect glutathione peroxidase activity. Such factors include
age, sex, ethnicity, iron-deficiency anemia, essential fatty acid deficiency,
and vitamin B12 deficiency.
