Anemia Screening

Etiology and Epidemiology

Anemia has multiple etiologies, each falling into 1 of 3 primary mechanisms:

• Decreased RBC production: Since RBCs have a lifespan of 90 to 120 days, continuous hematopoiesis is necessary to maintain normal levels. Any disruption to this process can result in a net loss of RBC mass over time, leading to anemia.[10]
• Increased RBC destruction: Conditions that destroy RBCs or significantly shorten their lifespan can outpace hematopoiesis, causing anemia.[11]
• Blood loss: Microscopic or macroscopic blood loss that exceeds the rate of RBC production results in anemia.[12]

These broad mechanisms can be further divided into specific causes, including but not limited to the following:

• Frank blood loss due to trauma or bleeding from an organ system (eg, otolaryngologic, gastrointestinal, genitourinary, or gynecologic)
• Nutritional deficiencies affecting hematopoiesis, such as iron, vitamin B12, folate, or generalized malnutrition
• Chronic disease or inflammation, including hepatic or renal disease, cancer, chronic infection, and collagen vascular disease
• Genetic disorders, such as thalassemia, hemoglobinopathies, and enzyme abnormalities in glycolysis; less common syndromes include Fanconi anemia, abetalipoproteinemia, and hereditary xerocytosis
• Infectious causes, including bacterial, viral, and protozoan infections, with malaria being a major global contributor
• Drug and chemical exposures leading to bone marrow suppression and anemia
• Primary or idiopathic bone marrow suppression
• Autoimmune diseases [13]

Epidemiological reporting of anemia is fragmented due to varying diagnostic criteria, with the U.S. using different standards than the WHO criteria, which are applied globally. Additionally, anemia prevalence varies across demographic, genetic, and geographic subsets. Best estimates suggest similar anemia prevalence in the U.S., Canada, and northern Europe, with approximately 4% of male individuals and 8% of female individuals meeting diagnostic thresholds in these regions. Data for the rest of the world remain more limited. Although available estimates are inexact, findings indicate that anemia occurs at rates 2 to 5 times higher worldwide than in the U.S., Canada, and northern Europe.[14][15][16]

Regions wherein populations commonly show higher rates of anemia include the following:

• Areas of Africa, India, and the Mediterranean basin with a higher prevalence of sickle cell disease
• Regions of the Mediterranean basin where thalassemia is more common
• Areas with endemic malaria or protozoal infections, where anemia of chronic disease is frequently observed
• Impoverished regions with an increased risk of nutritional anemia

Pathophysiology

Key Structures and Mechanisms in Anemia Pathophysiology

The development and regulation of RBCs involve complex interactions between the bone marrow, kidneys, and central nervous system (CNS). These interactions contribute to maintaining oxygen transport and vascular homeostasis. Understanding these mechanisms is essential for effectively diagnosing and managing anemia.

Red blood cells

RBCs are released from the bone marrow as reticulocytes. These immature cells contain a network of ribosomal RNA and mature into adult RBCs over 24 hours. The relative reticulocyte count helps determine whether the bone marrow is responding appropriately to anemia by increasing RBC production.[17]

Each RBC consists of 2 α and 2 β chains, along with a single heme moiety that reversibly binds oxygen. Although numerous genetic variants can alter the configuration of these chains, most do not cause clinical consequences. However, sickle cell disease and thalassemia variants affecting the α and β chains can lead to anemia. Additional genetic abnormalities involving the cell membrane, metabolism, or morphology are also recognized causes of anemia.[18]

Bone marrow

The bone marrow requires approximately 21 days to develop a pluripotent stem cell into a reticulocyte ready for circulation. The initial stimulus for reticulocyte production is the renal release of erythropoietin, which must remain present for the transformation of a pluripotent stem cell into a proerythroblast. This initial stage takes approximately 10 to 15 days. The next step, which is iron-dependent, takes 3 to 4 days, during which iron is incorporated into the proerythroblast to form a heme moiety, completing reticulocyte formation.[19][20]

Significant bone marrow-related causes of anemia include the following:

• Lack of essential substrates, such as iron, vitamin B12, or folate, needed for healthy reticulocyte production
• Direct suppression of bone marrow function due to medications, toxins, infections, or radiation exposure
• Replacement of bone marrow by neoplasm or fibrosis

Kidneys

The kidneys play a dual role in the pathophysiology of anemia. First, these organs produce 90% of the erythropoietin required to stimulate the transformation of pluripotent stem cells into proerythroblasts in the bone marrow. Any disruption in erythropoietin production or release leads to anemia.

Second, acute anemia caused by blood loss results in hypotension, which stimulates stretch receptors that send signals to the brain via the glossopharyngeal and vagus nerves. The resulting neural activity triggers several downstream effects, including the secretion of antidiuretic hormone, also known as arginine vasopressin or simply vasopressin. In response, the kidneys reabsorb water, reducing renal perfusion. The renin-angiotensin system is then activated, increasing vascular tone, stimulating aldosterone release, and ultimately raising intravascular volume.[21]

Central nervous system

The medulla, cerebral cortex, and pituitary gland coordinate the response to acute blood-loss anemia by increasing sympathetic tone. In addition, these CNS structures regulate volume changes by stimulating the secretion of antidiuretic hormone.[22]

Physiologic Response to Acute versus Chronic Anemia

Acute-onset anemia due to blood loss or rapid hemolysis is compensated by a CNS–directed, renal-mediated response to volume and perfusion loss.[23] This compensatory mechanism has an upper threshold, which is well-defined by the American College of Surgeons' Advanced Trauma Life Support protocols for managing volume loss:

• Class I hemorrhage: Up to 15% blood volume loss, no significant change in vital signs, no intervention required
• Class II hemorrhage: 15% to 30% blood volume loss, possible tachycardia, reduced pulse pressure, and peripheral vasoconstriction; volume repletion with crystalloids is typically sufficient, and blood transfusion is generally unnecessary
• Class III hemorrhage: 30% to 40% blood volume loss, resulting in hypotension, tachycardia, and shock; requires crystalloid resuscitation and blood transfusion
• Class IV hemorrhage: Greater than 40% blood volume loss, exceeding compensatory thresholds; lethal unless rapidly treated with blood products, crystalloids, and pressors

By contrast, very low hemoglobin levels may be tolerated in cases of chronic, slowly progressive anemia, where RBC mass is significantly reduced but circulating blood volume is preserved. The management of blood products and anemia-specific therapy, including RBC substrates or erythropoietin, depends on the underlying cause and clinical scenario.

Diagnostic Tests

The evaluation of anemia requires a range of laboratory tests and imaging studies selected based on clinical presentation and suspected etiology. The following tests may be relevant:

• Complete blood count: A complete blood count includes hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration.
• Reticulocyte count: This test serves as an estimate of bone marrow RBC output.
• Iron profile: This profile includes serum iron, ferritin, and total iron-binding capacity, which help assess iron stores and iron utilization.
• Peripheral blood smear: This test provides a microscopic evaluation of RBC morphology, which can aid in diagnosing structural abnormalities.
• Serum creatinine: This test helps assess renal function, which is crucial in cases where anemia may be secondary to kidney disease.
• Thyroid function tests: These tests include thyroxine and thyroid-stimulating hormone levels, which help evaluate anemia related to thyroid dysfunction.
• Coagulation screen: This panel includes activated partial thromboplastin time, prothrombin time, international normalized ratio, and thrombin time, which assist in evaluating bleeding tendencies.
• Liver function tests: This panel typically includes calcium, transaminases, total protein, bilirubin, albumin, and alkaline phosphatase. Additional liver function markers may include lactate dehydrogenase (LDH), γ-glutamyl transferase, and 5'-nucleotidase.
• Hemolysis profile: This profile includes haptoglobin, LDH, and indirect bilirubin, which help evaluate RBC destruction.
• Macrocytosis profile: This profile includes vitamin B12, folate, methylmalonic acid, and homocysteine levels, which help assess the causes of macrocytic anemia.
• Hemoglobin electrophoresis: This test evaluates hemoglobin amino acid chains, aiding in the diagnosis of hemoglobinopathies such as thalassemia or sickle cell disease.
• Abdominal sonogram: This imaging study assesses spleen size, which is relevant in cases of hemolytic anemia and hypersplenism.
• Bone marrow analysis: This procedure requires a hematology consultation and is used to evaluate bone marrow function and morphology.
• Inflammatory markers: C-reactive protein and erythrocyte sedimentation rate help identify anemia associated with chronic disease and systemic inflammation.
• Direct antiglobulin test: This assessment, also known as the Coombs test, detects immune-mediated hemolytic anemia by identifying antibodies bound to RBCs.
• Urinalysis: This test evaluates for the presence of hemoglobinuria or hemosiderinuria, which may indicate intravascular hemolysis.
• Erythropoietin level: This test helps evaluate erythropoiesis in cases of suspected renal anemia or bone marrow failure.
• Genetic testing: This test can confirm conditions such as hereditary spherocytosis, pyruvate kinase deficiency, or other rare hereditary anemias.
• Soluble transferrin receptor: This test differentiates between IDA and anemia of chronic disease.
• Vitamin B6 or copper levels: These tests may be considered in atypical or refractory cases of anemia.
• Computed tomography of the abdomen and pelvis: This imaging study is useful in cases of obscure gastrointestinal bleeding to locate sources of chronic blood loss.
• Capsule endoscopy: This procedure enables visualization of the small intestine for detecting occult bleeding.
• Osmotic fragility test: This test evaluates whether RBCs are more fragile than usual, which may indicate hereditary spherocytosis.
• Parvovirus B19 serology or DNA testing: This test helps identify transient red cell aplasia, particularly in immunocompromised patients.
• Glucose-6-phosphate dehydrogenase activity test: This test detects glucose-6-phosphate dehydrogenase deficiency, a common enzymatic cause of hemolytic anemia.
• Lead levels: This test assesses lead toxicity, which can contribute to anemia through disrupted hemoglobin synthesis, particularly in children.

Clinical considerations, patient history, and findings from the initial workup should guide the choice of tests. A systematic approach that considers both common and rare causes of anemia ensures accurate diagnosis and appropriate management.

Results, Reporting, and Critical Findings

A thorough patient history and physical examination are essential for guiding diagnostic testing and subsequent treatment. When clear clinical clues are present, the evaluation can be streamlined, allowing for targeted diagnostics and prompt initiation of appropriate therapy. If the cause of anemia remains unclear, a broader diagnostic approach is required to narrow potential etiologies systematically.

The differential diagnosis for anemia includes the following:

• Chronic disease and neoplasia
• Nutritional deficiency
• Injury
• Genetic illness
• Infection
• Autoimmune conditions
• Medication and chemical exposure

The initial assessment should determine whether the patient is actively bleeding and, if so, the extent of blood loss. This evaluation guides the urgency of intervention. The Advanced Trauma Life Support framework provides clear guidelines for managing trauma-related hemorrhage.[24]

The most common nontraumatic sources of bleeding include gastrointestinal, gynecologic, and genitourinary hemorrhage.[25] Hemodynamic stability remains the primary consideration in directing appropriate treatment. More subtle bleeding can occur in patients on anticoagulation or with occult chest, abdominal, or pelvic hemorrhage alongside hematoma formation. Management should focus on restoring blood volume and addressing the underlying cause of bleeding.[26]

If acute hemorrhage is unlikely, anemia should be categorized based on RBC size, hemoglobin concentration, and morphology on a peripheral blood smear. Anemia is classified as macrocytic, microcytic, or normocytic according to RBC size and as hypochromic or normochromic based on hemoglobin concentration. Characteristic RBC dysmorphisms may also be observed. Hemoglobin electrophoresis provides further insight into RBC abnormalities by assessing the structure of hemoglobin at the amino acid level.[27][28]

Two additional fundamental questions help refine the diagnosis:

• Is the bone marrow actively producing RBCs to compensate for anemia? The reticulocyte count and percentage, though somewhat nonspecific, provide the best peripheral estimate of bone marrow activity.

• Is hemolysis present? Elevated LDH, low haptoglobin, and increased indirect bilirubin are individually nonspecific for hemolysis but, when considered together, may indicate hemolysis.

With the above data, algorithms guide further evaluation based on RBC size. Microcytic anemia is further assessed using iron profile test results. Macrocytic anemia is differentiated based on vitamin B12, folate, methylmalonic acid, and homocysteine levels, with thyroid disease considered in some cases. Normocytic anemia is categorized based on whether it results from hemolysis, blood loss, or decreased bone marrow RBC production.

Red Blood Cell Transfusion Guidelines

According to the AAFP's position statement issued on March 15, 2011:

"Transfusion of RBCs should be based on the patient's clinical condition. Indications for RBC transfusion include acute sickle cell crisis or acute blood loss of greater than 1,500 cc or 30% of blood volume. Patients with symptomatic anemia should be transfused if they cannot function without treating the anemia."

The authors cite an updated Cochrane review supporting a restrictive transfusion trigger in patients with noncardiac disorders. The review advocates a hemoglobin threshold of 7 g/dL rather than the previously used 10 g/dL. Statistical analysis supports this revised threshold, showing a 54% relative decrease in the number of transfused blood units and an associated reduction in 30-day mortality rates with the updated criterion.[29][30]

Clinical Significance

In conclusion, anemia is not a diagnosis in itself but rather a clinical sign of an underlying condition that requires further evaluation. Anemia is an important indicator that should prompt healthcare providers to investigate potential causes, such as nutritional deficiencies (eg, iron, vitamin B12, or folate), chronic diseases, hemolytic disorders, bone marrow dysfunction, malignancies, or chronic kidney disease. Beyond being a diagnostic clue, anemia directly impacts patient health. Symptoms such as fatigue, weakness, shortness of breath, dizziness, and reduced exercise tolerance can significantly affect quality of life. In severe cases, anemia may lead to cardiovascular strain, impaired cognitive function, or organ damage due to inadequate oxygen delivery to tissues.

Anemia can also exacerbate existing comorbidities, further complicating patient management. In individuals with cardiovascular disease, anemia increases cardiac workload, potentially worsening heart failure or angina. In older adults, this manifestation may contribute to frailty, falls, and functional decline. Similarly, in individuals with chronic kidney disease, anemia can accelerate disease progression and diminish quality of life. Thus, managing anemia extends beyond correcting low hemoglobin levels. Effective treatment requires identifying and addressing the underlying cause while mitigating its broader impact on the patient’s overall health. A thorough evaluation—including a detailed history, physical examination, and targeted diagnostic testing—is essential to guiding appropriate therapy and improving clinical outcomes.

Quality Control and Lab Safety

Quality assurance in laboratories is a structured, systematic approach designed to ensure that all processes, procedures, and practices consistently yield reliable, accurate, and reproducible results. Quality assurance spans every phase of the testing cycle, including preanalytical, analytical, and postanalytical stages.[31] A key component of quality assurance is internal quality control (IQC), which focuses on the analytical phase to verify test accuracy before patient results are reported. IQC involves using control materials to monitor assay performance, a critical step in diagnosing conditions such as anemia through tests like complete blood count, serum ferritin, serum iron, total iron-binding capacity, transferrin saturation, and levels of vitamin B12 and folate.[32][33]

IQC entails daily monitoring with multilevel controls, ensuring instrument calibration, verifying reagent stability, and documenting performance to detect errors or trends. Statistical tools, such as Levey-Jennings charts, analyze control data, and corrective actions are taken promptly when results fall outside acceptable limits.[34] Complementing IQC, external quality assurance (EQA) programs assess laboratory performance by providing standardized, blinded specimens for analysis. Laboratories process these specimens using their routine methods and submit results for comparison against target values or peer group performance. This comparison helps identify analytical errors, biases, or discrepancies, prompting corrective measures to maintain test accuracy.[35][36]

Participation in quality assurance and EQA programs is essential for ensuring compliance with quality standards and improving the reliability of anemia-related tests. These programs enhance diagnostic precision and contribute to better patient outcomes through timely and accurate diagnoses.

Alongside quality standards, maintaining a safe laboratory environment is essential, particularly for laboratories conducting anemia screening. Safety protocols protect personnel, patients, and the environment while ensuring the accuracy of testing. Fundamental safety practices include adherence to biosafety guidelines, proper use of personal protective equipment, safe disposal of contaminated materials, and thorough training on handling blood-borne pathogens.[37]

Specific safety measures for anemia testing include using sterile, age-appropriate lancets, handling reagents according to safety data sheets, maintaining well-ventilated workspaces, and ensuring the functionality of safety equipment such as eyewash stations. Laboratories must also comply with standards, including guidelines from the International Organization for Standardization (ISO) 15190 and the Occupational Safety and Health Administration (OSHA), to uphold safety and regulatory requirements.[38]

Enhancing Healthcare Team Outcomes

The evaluation and management of anemia require an interprofessional approach. Anemia is a clinical sign that warrants investigation to determine its underlying cause. The impact of this condition extends beyond its direct medical effects, influencing comorbid disorders and overall patient health. A thorough patient history and physical examination guide diagnostic testing and treatment decisions. When clear clinical indicators are present, the workup may be streamlined, allowing for targeted diagnostic testing and appropriate therapeutic interventions. Healthcare team members who suspect anemia should pursue further evaluation and, when necessary, consult a hematologist for specialized expertise.