The definition of anemia: what is the lower limit of normal of the blood hemoglobin concentration?

Abstract

The diagnosis of anemia is an important aspect of the practice of hematology. The first step is to decide whether the patient is, in fact, anemic. Unless earlier blood counts are available, and they often are not, the physician must make his or her decision on the basis of the population distribution of hemoglobin values. How likely is it that the patient's hemoglobin value lies below the normal distribution; that is, "the lower limit"?

Figure 1.

A reproduction of the page of the WHO report that has been used as a standard for anemia in epidemiologic studies. The casual treatment of the lower level of normal, given in whole numbers without decimal points in this 40-page document dealing with nutritional anemia, clearly suggests that the authors never intended for these values to become a hallowed international standard. (From Nutritional Anaemias. Report of a WHO Scientific Group. WHO Tech Rep Ser. 1968;405:1-40; with permission.)

Figure 2.

The mean and -1.65 standard deviations of the hemoglobin values of the white subjects in the Scripps-Kaiser and NHANES-III databases after applying the criteria described in the text. The bottom of the error bars represents the hemoglobin value below which only 5% of normal values would be predicted to be present.