Diagnosing and Classifying Anemia in Adult Primary Care

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Anemia affects more than 3 million people in the United States, making it a common problem in primary care practices. Once anemia is detected, clinicians must define the type and identify its underlying cause prior to initiating treatment. In most cases, the cause can be determined using information from the patient history, physical exam, and complete blood count.

Anemia is commonly identified during routine physical exams and laboratory testing.1-3 However, treating anemia can present a challenge for the primary care provider if the immediate cause is not apparent. Iron deficiency is a leading cause of anemia, but simply prescribing an iron supplement without determining the type or the cause of the anemia is not appropriate. Anemia that is misdiagnosed or goes untreated can be associated with a worse prognosis, as well as increased health care costs.4

Primary care providers often manage patients with common types of anemia and refer patients with severe or complex anemia to specialists for further testing and treatment. The most commonly used and cost-effective diagnostic tool for anemia is the complete blood count (CBC).2-6 The CBC provides details that can help the provider determine the type of anemia present, which in turn guides proper diagnostic testing and treatment.


Anemia involves a reduction in the number of circulating red blood cells, the blood hemoglobin content, or the hematocrit, which leads to impaired delivery of oxygen to the body. Anemia affects more than 2 billion people worldwide, with iron deficiency the most common cause.7 Other leading nutritional causes of anemia include vitamin B12 and folate deficiency.4,7 Approximately 3 to 4 million Americans have anemia in some form, and it affects about 6.6% of men and 12.4% of women.5,8 The prevalence of anemia increases with age. Approximately 11% of men and 10% of women ages 65 or older have anemia, and in men ages 85 or older, prevalence of 20% to 44% has been reported.1,4 Anemia is present in about 3.5% of patients with chronic disease, but only 15% of them receive treatment.4

Diagnosing and Classifying Anemia in Adult Primary Care image


Blood is composed of water-based plasma (54%), white blood cells and platelets (1%), and red blood cells (45%).5 Hemoglobin, the primary protein of the red blood cell, binds oxygen from the lungs and transports it to the rest of the body. Oxygen is then exchanged for carbon dioxide, which is carried back to the lungs to be exhaled.

Hemoglobin is made up of four globin chains, each containing an iron ion held in a porphyrin ring known as a heme group.5 When the body detects low tissue oxygen, the endothelial cells in the kidneys secrete the hormone erythropoietin (EPO), which stimulates the bone marrow to increase red cell production.5 This feedback loop can be interrupted by renal failure or chronic disease.4 In addition, bone marrow cannot produce enough red blood cells if there are insufficient levels of iron, amino acids, protein, carbohydrates, lipids, folate, and vitamin B12.5 Toxins (eg, lead), some types of cancer (eg, lymphoma), or even common infections (eg, pneumonia) can suppress the bone marrow, causing anemia. The more severe the anemia, the more likely oxygen transport will be compromised and organ failure will ensue.

Mutations affecting the genes that encode the globin chains within hemoglobin can cause one of the more than 600 known hemoglobinopathies (genetic defects of hemoglobin structure), such as sickle cell disease and thalassemias.5,9 While it is important to identify and treat patients with hemoglobinopathies, most anemias have other causes, such as iron deficiency, chronic disease, bone marrow defects, B12 deficiency, renal failure, medications, alcoholism, pregnancy, nutritional intake problems, gastrointestinal malabsorption, and active or recent history of blood loss.5,10


There are several signs and symptoms that should lead the primary care provider to suspect anemia (see Table 1).5,6 The severity of these symptoms can vary from mild to very serious. Severe anemia can lead to organ failure and death. However, most patients with anemia are asymptomatic, and anemia is typically detected incidentally during laboratory testing.1,2

Signs and Symptoms Associated With Anemia image

Once anemia is confirmed, the evaluation focuses on diagnosing its underlying cause. It should include a thorough patient history and review of systems to ascertain whether the patient has symptoms such as increased fatigue, palpitations, gastrointestinal distress, weakness, or dizziness.

If the provider has access to past CBC results, a comparison of the current and previous results will help determine whether the anemia is acute or chronic. Anemia caused by acute conditions, such as a suspicion of blood loss or bone marrow suppression, must be attended to immediately. A patient with chronic anemia should be carefully monitored and may need follow-up for ongoing treatment. While a provider has more time to work up a patient with chronic anemia, the causes may not be as straight­forward.


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