Iron: nutrition monitoring and nutrition status assessment.

The majority of anemias in the United States are characterized by low mean corpuscular volume and thus are classified as microcytic. Iron deficiency, chronic disease and thalassemia traits are the three leading causes of microcytic anemia. The true cause of anemia must always be sought so that the prevalence estimates of iron deficiency are accurate and so that appropriate treatment can be initiated for the anemic individual. In both the clinical setting and in surveys, the most frequent differential diagnosis of microcytic anemia will involve distinguishing between iron deficiency and chronic disease. Erythrocyte sedimentation rate (ESR), zeta-sedimentation rate (ZSR), and C-reactive protein (CRP) are elevated in a variety of diseases. These indicators may help differentiate the anemia of chronic disease from iron deficiency, so that iron deficiency is not overestimated in hospitalized and aged populations. The red cell distribution width (RDW) appears to be elevated to a greater extent in iron deficiency than in chronic disease or thalassemia traits. RDW and CRP are two of several indicators of iron status in the third National Health and Examination Survey (NHANES III).