Diagnosis of anemia and iron deficiency: analytic and biological variations of laboratory tests.

We describe the magnitude of analytic errors and the within-subject biological variations for laboratory tests that are used in the diagnosis of anemia and iron deficiency. For Hb, hematocrit, and red cell indices, coefficients of variation for analytic and biological variations are less than 4%. In general, higher coefficients of variation are characteristic of serum iron, iron-binding capacity, serum ferritin, and erythrocyte protoporphyrin. Particularly high analytic variations between different laboratories have been described for iron-binding capacity and the greatest biological variations have been noted for serum iron. An awareness of these sources of error is helpful in designing studies and in interpreting laboratory results.