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Current Trends CDC Criteria for Anemia in Children and Childbearing-Aged Women

Hemoglobin (Hb) and hematocrit (Hct) measurements are the laboratory tests used most commonly in clinical and public health settings for screening for anemia. Because most anemia in children and women of childbearing age is related to iron deficiency (1), the main purpose of anemia screening is to detect those persons at increased risk for iron deficiency. Proper anemia screening requires not only sound laboratory methods and procedures but also appropriate Hb and Hct cutoff values to define anemia. The "normal" ranges of Hb and Hct change throughout childhood and during pregnancy, and are higher for men than women (1,2). Thus, criteria for anemia should be specific for age, sex, and stage of pregnancy. Current major reference criteria for anemia, however, are not based on representative samples and fail to take into account the normal hematologic changes occurring during pregnancy. To address these limitations, CDC has formulated new reference criteria for use in clinical practice for public health and nutrition programs and the CDC Pediatric and Pregnancy Nutrition Surveillance Systems. The new criteria may also be useful for defining anemia in clinical research and nutrition surveys.

The anemia reference values for children, nonpregnant women, and men are derived from the most current nationally representative sample--the Second National Health and Nutrition Examination Survey, 1976-1980 (NHANES II). Because representative data are not yet available for pregnant women, anemia reference values are based on the most current clinical studies available. Adjustment values of Hb and Hct cutoffs are provided for persons who reside at higher altitudes and for those who smoke cigarettes. Anemia Cutoffs for Children, Nonpregnant Women, and Men

Because hematologic values normally change as children grow older, it is necessary to use age-specific criteria for diagnosing anemia in children (1). The best hematologic reference data for the United States are available from the NHANES II. The Hb and Hct cutoffs recommended represent the age-specific fifth percentile values for "healthy" persons from NHANES II (Table 1) (3,4). The healthy sample was defined by excluding persons who were likely to have iron deficiency based on multiple iron biochemical measures. The anemia cutoff values based on these NHANES II studies for younger children are in close agreement with the cutoff values recommended by the American Academy of Pediatrics, which were based on a sample of healthy white middle-class children (5). Even though no data are available from NHANES II to determine anemia cutoffs for infants less than 1 year of age, cutoff values for children 1-2 years can be extrapolated back to 6 months of age. In general, anemia screening to detect iron deficiency is not indicated for infants less than 6 months of age because younger infants usually have adequate iron nutritional status (6). Anemia Cutoffs during Pregnancy

During a normal pregnancy, a woman's hematologic values change substantially (2). For women with adequate iron nutrition, Hb and Hct values start to decline during the early part of first trimester, reach their nadir near the end of second trimester, then gradually rise during the third trimester (2,7-10). Because of the change of Hb and Hct during pregnancy, anemia must be characterized according to the specific stage of pregnancy. The normal range of Hb and Hct during pregnancy is based on data aggregated from four European studies of healthy iron-supplemented pregnant women (7-10). These studies provide similar findings at each specific month of pregnancy. The month-specific fifth percentile values for Hb of the pooled data have been adopted for use in the CDC Pregnancy Nutrition Surveillance System (Table 2). In addition, trimester-specific cutoffs also have been developed for use in the clinical setting (Table 2). These trimester-specific cutoffs are based on the mid-trimester values; cutoffs for the first trimester, the time at which most women are initially seen for prenatal care, are based on a late-trimester value. Adjustment of Hb and Hct Cutoffs for Altitude and Smoking

Persons residing at higher altitudes ( greater than 1000 meters (3300 feet)) have higher Hb and Hct levels than those residing at sea level. This variation is due to the lower oxygen partial pressure at higher altitudes, a reduction in oxygen saturation of blood (11), and a compensatory increase in red cell production to ensure adequate oxygen supply to the tissues. Thus, higher altitude causes a generalized upward shift of the Hb and Hct distributions. This shift may be associated with the underdiagnosis of anemia for residents of higher altitudes when sea-level cutoffs are applied (CDC, unpublished data). Therefore, the proper diagnosis of anemia for those residing at higher altitudes requires an upward adjustment of Hb and Hct cutoffs. The values for altitude-specific adjustment of Hb and Hct are derived from data collected by the CDC Pediatric Nutrition Surveillance System on children residing at various altitudes in the mountain states (Table 3). Altitude affects Hb and Hct levels throughout pregnancy in a similar way (J.N. Chatfield, unpublished data).

The influence of cigarette smoking is similar to that of altitude, in that smoking increases Hb and Hct levels substantially. The higher Hb and Hct of smokers is a consequence of an increased carboxyhemoglobin from inhaling carbon monoxide during smoking. Because carboxyhemoglobin has no oxygen carrying capacity, its presence causes a generalized upward shift of the Hb and Hct distribution curves (CDC, unpublished data). Therefore, a smoking-specific adjustment to the anemia cutoff is necessary for the proper diagnosis of anemia in smokers. The smoking-specific Hb and Hct adjustments are derived from the NHANES II data (Table 4). The altitude and smoking adjustments are additive. For example, a woman living at 6000 feet and smoking two or more packs of cigarettes per day would have her cutoff for anemia adjusted upward by a total of 1.4 grams of Hb or 4% Hct. Reported by: Div of Nutrition, Center for Chronic Disease Prevention and Health Promotion; Div of Environmental Health Laboratory Sciences, Center for Environmental Health and Injury Control; Div of Health Examination Statistics, National Center for Health Statistics; Div of Host Factors, Center for Infectious Diseases, CDC.

References

  1. Dallman PR, Yip R, Johnson C. Prevalence and causes of anemia in

the United States, 1976 to 1980. Am J Clin Nutr 1984;39:437-45.

2. Bothwell TH, Charlton RW. Iron deficiency in women: a report of the International Nutritional Anemia Consultative Group (INACG). New York: The Nutrition Foundation, 1981.

3. Pilch SM, Senti FR, eds. Assessment of the iron nutritional status of the U.S. population based on data collected in the Second National Health and Nutrition Examination Survey, 1976-1980. Bethesda, Maryland: Federation of American Societies for Experimental Biology, Life Sciences Research Office, 1984.

4. Yip R, Johnson C, Dallman PR. Age-related changes in laboratory values used in the diagnosis of anemia and iron deficiency. Am J Clin Nutr 1984;39:427-36.

5. American Academy of Pediatrics. Pediatric nutrition handbook. 2nd ed. Elk Grove Village, Illinois: American Academy of Pediatrics, Committee on Nutrition, 1985. 6. Smith NJ, Rosello S, Say MB, Yeya K. Iron storage in the first five years of life. Pediatrics 1955;16:166-71.

7. Svanberg B, Arvidsson B, Norrby A, Rybo G, Solvell L. Absorption of supplemental iron during pregnancy: a longitudinal study with repeated bone-marrow studies and absorption measurements. Acta Obstet Gynecol Scand Suppl 1975;48:87-108.

8. Sjostedt JE, Manner P, Nummi S, Ekenved G. Oral iron prophylaxis during pregnancy: a comparative study on different dosage regimens. Acta Obstet Gynecol Scand Suppl 1977;60:3-9.

9. Puolakka J, Janne O, Pakarinen A, Jarvinen A, Vihko R. Serum ferritin as a measure of iron stores during and after normal pregnancy with and without iron supplements. Acta Obstet Gynecol Scand Suppl 1980;95:43-51. 10. Taylor DJ, Mallen C, McDougall N, Lind T. Effect of iron supplementation on serum ferritin levels during and after pregnancy. Br J Obstet Gynecol 1982;89:1011-7. 11. Hurtado A, Merino C, Delgado E. Influence of anoxemia on the hemopoietic activity. Arch Intern Med 1945;75:284-323.

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