Anemia is a common problem that is often discovered on routine laboratory tests. Its prevalence increases with age, reaching 44 percent in men older than 85 years. Normocytic anemia is the most frequently encountered type of anemia. Anemia of chronic disease, the most common normocytic anemia, is found in 6 percent of adult patients hospitalized by family physicians. The goals of evaluation and management are to make an accurate and efficient diagnosis, avoid unnecessary testing, correct underlying treatable causes and ameliorate symptoms when necessary. The evaluation begins with a thorough history and a careful physical examination. Basic diagnostic studies include the red blood cell distribution width, corrected reticulocyte index and peripheral blood smear; further testing is guided by the results of these studies. Treatment should be directed at correcting the underlying cause of the anemia. A recent advance in treatment is the use of recombinant human erythropoietin. (Am Fam Physician 2000; 62:2255-63,2264.)
Anemia is defined as a decrease in the circulating red blood cell mass to below age-specific and gender-specific limits. In normocytic anemias, the mean corpuscular volume (MCV) is within defined normal limits, but the hemoglobin and hematocrit are decreased. The MCV is also age-specific (Figure 1),(1) with normal values ranging from 70 femtoliter (fL) at one year of age to 80 fL at seven years and older.(2)
Most patients with anemia are asymptomatic. Therefore, the condition is most often discovered by laboratory evaluation, usually on routine testing as part of the general physical examination or for reasons other than suspected anemia. Anemia should be considered a sign, not a disease.(3) It can be caused by a variety of systemic disorders and diseases, as well as primary hematologic disorders.
Approximately 4.7 million Americans have anemia.(4) Population-based estimates indicate that this condition affects 6.6 percent of males and 12.4 percent of females. The prevalence of anemia increases with age and is 44.4 percent in men 85 years and older.(5) Although the elderly are more prone to develop anemia, older age is not of itself a cause of the condition.(6)
Etiology
Normocytic anemias may be thought of as representing any of the following: a decreased production of normal-sized red blood cells (e.g., anemia of chronic disease, aplastic anemia); an increased destruction or loss of red blood cells (e.g., hemolysis, posthemorrhagic anemia); an uncompensated increase in plasma volume (e.g., pregnancy, fluid overload); or a mixture of conditions producing microcytic and macrocytic anemias.
It should be noted that in the initial stage, nearly all anemias are normocytic. The major primary causes of normocytic anemia are given in Table 1.
Decreased Red Blood Cell
Production
ANEMIA OF CHRONIC DISEASE
Anemia of chronic disease is the most common normocytic anemia and the second most common form of anemia worldwide (after iron deficiency anemia).(7) The MCV may be low in some patients with this type of anemia. The pathogenesis of anemia of chronic disease is multifactorial and is related to hypoactivity of the bone marrow, with relatively inadequate production of erythropoietin or a poor response to erythropoietin, as well as slightly shortened red blood cell survival.
Anemia of chronic disease is associated with a wide variety of chronic disorders, including inflammatory conditions, infections, neoplasms and various systemic diseases. The diagnosis of anemia of chronic disease is not usually applied to the anemias associated with renal, hepatic or endocrine disorders. Patients with these disorders may not display the hallmark ferrokinetic profile of anemia of chronic disease (i.e., decreased serum iron level, decreased transferrin level, or normal or elevated ferritin levels, all of which result in iron being present but inaccessible for use). (3,8-10)
ENDOCRINE DEFICIENCY
Endocrine deficiency states, including hypothyroidism, adrenal or pituitary insufficiency, and hypogonadism, may cause secondary bone marrow failure because of reduced stimulation of erythropoietin secretion. Hyperthyroidism may also cause normocytic anemia.(3,9)
RENAL FAILURE
Anemia occurs in acute and chronic renal failure. The anemia is usually normocytic but may be microcytic. In renal failure, anemia occurs in part because uremic metabolites decrease the lifespan of circulating red blood cells and reduce erythropoiesis.
Anemia secondary to uremia is characterized by inappropriately low erythropoietin levels, in contrast to the normal or high levels that occur with most other causes of anemia. To further confuse the presentation, serum iron levels and the percentage of iron saturation are often low, apparently because of negative acute-phase reactions.(10) Furthermore, the serum creatinine level and the degree of anemia may not correlate well.(3)
OTHER CAUSES
Other causes of decreased red blood cell production include bone marrow infiltration, fibrosis, various myeloproliferative diseases and sideroblastic anemias. These uncommon disorders are generally diagnosed by bone marrow biopsy.
Increased Red Blood Cell Destruction or Loss
HEMOLYTIC ANEMIAS
Hemolytic anemias other than the alloimmune hemolytic anemias of newborns (e.g., Rh or ABO incompatibility) can be categorized as congenital or acquired (Table 2).(3,9,11-13)
Congenital hemolytic anemias include the hemoglobinopathies (homozygous sickle cell disease [hemoglobin SS disease], heterozygous sickle hemoglobin C disease [hemoglobin SC disease]), red blood cell membrane disorders and red blood cell enzyme deficiencies.(11,12)
Homozygous sickle cell disease is the most common cause of hemolytic normocytic anemias in children. Because of longevity, this disease is also becoming an increasingly prevalent cause of these anemias in adults.(11-13)
Hereditary spherocytosis is the most common red blood cell membrane disorder. It usually presents in childhood with anemia, jaundice and splenomegaly. Pigment gallstones, delayed growth and dysmorphic features may occur. Hereditary elliptocytosis ranges from an asymptomatic carrier state to severe hemolytic anemia.(11-13)
Red blood cell enzyme deficiencies include glucose-6-phosphate dehydrogenase (G6PD) and pyruvate kinase deficiencies. More than 300 varieties of G6PD deficiency have been identified. The southern Mediterranean variety, referred to as "favism," is best known, but the most common variant in the United States is a less severe X-linked disorder that affects 10 percent of black males. Persons with the U.S. variant may experience an acute, self-limited hemolytic episode after exposure to causes of oxidative stress, including sulfa drugs, nitrofurantoin (Furadantin), phenazopyridine (Pyridium) and antimalarial drugs.(11,12)
Acquired hemolytic anemias include autoimmune hemolytic anemias, mechanical hemolysis and paroxysmal nocturnal hemoglobinuria.(12) Autoimmune hemolytic anemias primarily occur in persons older than 40 years. The most common and typically most severe of these anemias are those caused by warm-reactive antibodies. Autoimmune hemolytic anemias caused by cold-reactive antibodies most commonly follow Mycoplasma pneumonia or infectious mononucleosis.
Drugs that induce autoimmune hemolytic anemias include methyldopa (Aldomet), penicillins, cephalosporins, erythromycin, acetaminophen (e.g., Tylenol) and procainamide (Pronestyl).
Paroxysmal nocturnal hemoglobinuria generally presents as a chronic hemolytic anemia. Classic nocturnal hemoglobinuria is seldom seen.(12)
UNCOMPENSATED BLOOD LOSS
Acute posthemorrhagic anemia occurs with gastrointestinal bleeding, bleeding from an external wound or, less obviously, retroperitoneal bleeding or bleeding into a hip fracture. A healthy young person would be expected to tolerate rapid loss of 500 to 1,000 mL of blood (10 to 20 percent of the total blood volume) with few or no symptoms, although about 5 percent of the general population would have a vasovagal reaction.(14) Indeed, healthy young persons at rest may tolerate an acute isovolemic reduction of hemoglobin volume to a level of 5 g per dL (50 g per L) without impairment of critical oxygen delivery.(15)
HYPERSPLENISM
Hypersplenism leads to anemia only after the spleen reaches three to four times its normal size, as may occur in cirrhosis, chronic infections and myeloproliferative diseases. The anemia is primarily caused by the removal of red blood cells from the circulation, but increased destruction of red blood cells is usually a contributing factor.(16)
Normocytic Anemia in Children
The prevalence of anemias caused by iron deficiency or lead toxicity continues to decline in the United States.(17) As a result, normocytic anemias are constituting a larger proportion of cases in the pediatric age group.
Iron deficiency, which in its early stages is usually characterized by a normal MCV, is still a common cause of mild normocytic anemia in children beyond the neonatal period. Other common childhood normocytic anemias are the result of acute bleeding, sickle cell anemia, red blood cell membrane disorders and current or recent infections (particularly in younger children).(2,17) Aplastic crises in patients of any age who have chronic hemolytic anemias are frequently precipitated by human parvovirus B19 infection.(2,12,13,18)
Most anemias in children can be diagnosed with a basic work-up that includes a complete blood cell count (CBC), a corrected reticulocyte index, a peripheral blood smear and targeted studies of the peripheral blood (e.g., hemoglobin electrophoresis).
Although bone marrow examinations are generally unnecessary, one study found that when the basic laboratory studies and historical and physical evidence were unrevealing, bone marrow specimens yielded a specific diagnosis in 92 percent of children.(18) The most frequent diagnosis in this study was transient erythroblastopenia of childhood, a common, generally mild, self-limited red blood cell aplasia of unknown etiology. This entity must be distinguished from Blackfan-Diamond syndrome, a rare, usually macrocytic and probably genetic disorder of infants. Blackfan-Diamond syndrome is a congenital erythroid hypoplasia that usually does not spontaneously remit.(3,9)
Diagnosis
Physicians are sometimes inefficient in their evaluation of normocytic anemia, either ordering an excessive battery of tests or foregoing testing entirely in the belief that a cause is not likely to be found.(19) The first step in the evaluation of anemia is to correlate the finding of anemia with the information obtained from the patient's history and physical examination. In many instances, this approach allows a working diagnosis to be made and many disorders to be eliminated.
Most published algorithms for the diagnosis of normocytic anemia begin with an examination of the peripheral blood smear(20) or a corrected reticulocyte index.(2,9,21) The red blood cell distribution width is a measure of the variability of the size (anisocytosis) of the cells and is usually reported as a component of automated CBCs. Therefore, a practical and useful first step is to use the red blood cell distribution width to help categorize the normocytic anemia as heterogeneous (e.g., hemolytic anemia) or homogeneous (e.g., anemia of chronic disease).(2) In patients with a mild homogeneous normocytic anemia (hematocrit of 30 percent or greater) and a known chronic disease, anemia of chronic disease is highly likely, and bone marrow biopsy may not be necessary (Figure 2).(21)
'DRAW AND HOLD' STRATEGY
Because the diagnosis of normocytic anemia usually proceeds in a step-wise fashion that begins with the corrected reticulocyte index and examination of the peripheral blood smear, a patient-friendly, cost-effective and time-efficient strategy is to use a "draw and hold" order for possible later testing. Most laboratories do not charge to hold tubes, and tests can usually be added up to one week after specimens are obtained. The physician should check with the local laboratory to determine the number and type of specimens that need to be obtained.
PERIPHERAL BLOOD SMEAR
The examination of the peripheral blood smear often yields diagnostic clues or confirmatory evidence. Easily recognized red blood cell findings related to normocytic anemias include the following: large polychromatic "shift cells," which represent reticulocytosis; target cells, which may be found in liver disease; basophilic stippling, which may be present in hemolytic anemias; and mixtures of large and small red blood cells, which may suggest the presence of mixed microcytic and macrocytic disease processes (a finding that should be suggested by an elevated red blood cell distribution width).
Other findings include burr cells (uremia), spherocytes (hereditary spherocytosis, autoimmune hemolysis, G6PD deficiency), elliptocytes (hereditary elliptocytosis), schistocytes (microangiopathic processes), bite or blister cells (where all of the hemoglobin appears to be pushed to one side of the cell, G6PD deficiency) and nucleated red blood cells (hemolytic anemia, acute blood loss). These findings may be present in other anemias and in other conditions.(3,9,10)
The corrected reticulocyte index, along with the white blood cell and platelet counts, indicates whether the bone marrow is functioning appropriately. The corrected reticulocyte index should be elevated in patients with an acute anemia but a competent bone marrow.
ILLUSTRATIVE CASES
Case 1. A 50-year-old woman who had been taking aspirin for a flare of rheumatoid arthritis presented with mild epigastric pain. A CBC was ordered, and a guaiac test for occult blood was performed. The guaiac test was negative.
The CBC revealed a normocytic anemia (hemoglobin count, 11 per mm3 [11 3 106 per L]; hematocrit, 33 percent [0.33]; MCV, 84 fL), with a red blood cell distribution width of 41 fL (normal range: 39 to 47 fL). A reticulocyte count and "draw and hold" specimens were ordered. The corrected reticulocyte index was 1.0 percent.
Ferritin and serum iron levels were obtained from the stored specimens. These tests revealed an elevated ferritin level and a low serum iron level, findings consistent with a diagnosis of anemia of chronic disease related to the patient's rheumatoid arthritis.
Case 2. A 44-year-old woman presented with the complaint of fatigue. Her physical examination was unremarkable.
A CBC revealed normocytic anemia (hemoglobin count, 11 per mm3 [11 3 106 per L]; hematocrit, 33 percent [0.33]; MCV, 84 fL), with an elevated red blood cell distribution width of 53 fL. A reticulocyte count and "draw and hold" specimens were ordered. The corrected reticulocyte index was elevated (3.6 percent).
Examination of a peripheral blood smear from the stored specimens was normal. A direct antiglobulin test (direct Coombs' test) was positive, and a preliminary diagnosis of autoimmune hemolytic anemia was made.
Treatment
The treatment of a normocytic anemia begins with timely identification of its cause. In most patients, therapy is individualized to the underlying disorder. Treatments may include avoidance of trigger exposure in patients with hemolytic anemia, correction of iron, folate or vitamin B12 deficiency in patients with mixed disorders, or splenectomy in patients with hypersplenism.(12,13)
Anemia of renal disease is associated with a relative underproduction of erythropoietin, and inappropriate erythropoietin levels appear to contribute significantly to anemia of chronic disease. With the development of recombinant human erythropoietin (r-HuEPO; epoetin alfa [Epogen]), there has been considerable interest in finding out whether exogenous erythropoietin administration would improve anemia.
The effects of r-HuEPO administration have been studied in a variety of disorders. In a trial conducted in 1990,(22) all 11 patients with anemia related to rheumatoid arthritis reached a normal hematocrit after 24 weeks. Since then, r-HuEPO has been tested in patients with anemia of chronic disease secondary to acquired immunodeficiency syndrome, malignancy, inflammatory bowel disease, renal disease and other disorders.(23,24) Quality-of-life parameters in responders improved significantly.
Therapy with r-HuEPO is very expensive and should never replace treatment of the underlying cause of an anemia. R-HuEPO is an indicated therapy for anemia of renal disease. In this situation, its use should be based on clinical and quality-of-life issues rather than specific hemoglobin levels.(10) There are no consistent guidelines for r-HuEPO therapy in patients with anemia of chronic disease, although response rates of 40 to 80 percent may be achieved.(8)
Erythropoietin also appears to be useful prophylactically in patients undergoing autologous blood donation and certain surgical procedures.(25)
In all patients, treatment of anemia should include the provision of optimal nutrition and supportive care.
REFERENCES
(1.) Dallman PR, Siimes MA. Percentile curves for hemoglobin and red cell volume in infancy and childhood. J Pediatr 1979;94:26-31.
(2.) Bessman JD, Gilmer PR, Gardner FH. Improved classification of anemias by MCV and RDW. Am J Clin Pathol 1983;80:322-6.
(3.) Schnall SF, Berliner N, Duffy TP, Benz EF Jr. Approach to the adult and child with anemia. In: Hoffman R, et al., eds. Hematology: basic principles and practice. 3d ed. New York: Churchill Livingstone, 2000:367-82.
(4.) Adams PF, Marano MA. Current estimates from the National Health Interview Survey, 1994. Hyattsville, Md.: U.S. Dept. of Health and Human Services, Public Health Service, Centers for Disease Control, National Center for Health Statistics, 1995. Vital and health statistics. Series 10: Data from the National Health Survey; no. 193; DDHS publication no. (PHS) 95-1521.
(5.) Ania BJ, Suman VJ, Fairbanks VF, Melton LJ 3d. Prevalence of anemia in medical practice: community versus referral patients. Mayo Clin Proc 1994; 69:730-5.
(6.) Izaks GJ, Westendorp RG, Knook DL. The definition of anemia in older persons. JAMA 1999;281:1714-7.
(7.) Krantz SB. Pathogenesis and treatment of the anemia of chronic disease. Am J Med Sci 1994;307: 353-9.
(8.) Gardner LB, Benz EJ Jr. Anemia of chronic diseases. In: Hoffman R, et al., eds. Hematology: basic principles and practice. 3d ed. New York: Churchill Livingstone, 2000:383-8.
(9.) Lee GR. Anemia: a diagnostic strategy. In: Lee GR, et al., eds. Wintrobe's Clinical hematology. 10th ed. Baltimore: Williams & Wilkins, 1999:908-40.
(10.) Abramson SD, Abramson N. 'Common' uncommon anemias. Am Fam Physician 1999;59:851-8.
(11.) Weatherall DJ. ABC of clinical haematology. The hereditary anaemias. BMJ 1997;314:492-6.
(12.) Sackey K. Hemolytic anemia: Part 1. Pediatr Rev 1999;20:152-8.
(13.) Sackey K. Hemolytic anemia: Part 2. Pediatr Rev 1999;20:204-8.
(14.) Levine E, Rosen A, Sehgal L, Gould S, Sehgal H, Moss G. Physiologic effects of acute anemia: implications for a reduced transfusion trigger. Transfusion 1990;30:11-4.
(15.) Weiskopf RB, Viele MK, Feiner J, Kelley S, Lieberman J, Noorani M, et al. Human cardiovascular and metabolic response to acute, severe isovolemic anemia. JAMA 1998;279:217-21 [Published erratum appears in JAMA 1998;280:1404].
(16.) Erslev AJ. Hypersplenism and hyposplenism. In: Beutler E, Lichtman MA, et al., eds. Williams Hematology. 5th ed. New York: McGraw-Hill, Health Professions Division, 1995:709-14.
(17.) Sherry B, Bister D, Yip R. Continuation of decline in prevalence of anemia in low-income children: the Vermont experience. Arch Pediatr Adolesc Med 1997;151:928-30.
(18.) Abshire TC. The anemia of inflammation. A common cause of childhood anemia. Pediatr Clin North Am 1996;43:623-37.
(19.) Meyers FJ, Welborn JL, Lewis JP. Improved approach to patients with normocytic anemia. Am Fam Physician 1988;38(2):191-5.
(20.) Farhi DC, Luebbers EL, Rosenthal NS. Bone marrow biopsy findings in childhood anemia: prevalence of transient erythroblastopenia of childhood. Arch Pathol Lab Med 1998;122:638-41.
(21.) Brown RG. Normocytic and macrocytic anemias. Postgrad Med 1991;89(8):125-32,135-6.
(22.) Pincus T, Olsen NJ, Russell IJ, Wolfe F, Harris ER, Schnitzer TJ, et al. Multicenter study of recombinant human erythropoietin in correction of anemia in rheumatoid arthritis. Am J Med 1990;89:161-8.
(23.) Krantz SB. Erythropoietin and the anaemia of chronic disease. Nephrol Dial Transplant 1995; 10(suppl 2):10-7.
(24.) Ludwig H, Fritz E, Kotzmann H, Hocker P, Gisslinger H, Barnas U. Erythropoietin treatment of anemia associated with multiple myeloma. N Engl J Med 1990;322:1693-9.
(25.) Goodnough LT, Monk TG, Andriole GL. Erythropoietin therapy. N Engl J Med 1997;336:933-8.
The Authors
JOHN R. BRILL, M.D., is assistant professor and medical director of Community Health Programs in the Department of Family Medicine at the Milwaukee Clinical Campus of the University of Wisconsin Medical School. Dr. Brill graduated from the Medical College of Wisconsin, Milwaukee, and completed a faculty development fellowship and residency at St. Luke's Medical Center, also in Milwaukee.
DENNIS J. BAUMGARDNER, M.D., is professor and residency director at St. Luke's Family Practice Residency Program, which is affiliated with the Department of Family Medicine at the Milwaukee Clinical Campus of the University of Wisconsin Medical School. Dr. Baumgardner graduated from the University of Illinois at Chicago College of Medicine and completed a family medicine residency at the Rockford (Ill.) Medical Education Foundation.
Address correspondence to John R. Brill, M.D., St. Luke's Family Practice Residency, 2801 W. Kinnickinnic River Pkwy., Suite 175, Milwaukee, WI 53215 (e-mail: jbrill@ fammed.wisc.edu). Reprints are not available from the authors.
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