Biochemical and histological methodologies for assessing vitamin A status in human populations.

In recent years, new biochemical and histological methodologies have been developed for assessing vitamin A nutritional status in humans at subclinical levels of nutriture. Insensitive static blood levels no longer are the only practical assessment parameter. Some of the newer functional methodologies require additional testing of their sensitivity and specificity under a variety of conditions existing in human populations and that frequently are associated with an inadequate vitamin A status. Some of these conditions could confound the interpretation when only a single assessment method is applied.