How should I assess a patient for anemia?

Assessment of Anemia: A Structured Approach

Begin by obtaining a complete blood count (CBC) with hemoglobin measurement as your primary screening tool, defining anemia as hemoglobin <13.0 g/dL in men and <12.0 g/dL in women. 1, 2

Initial Laboratory Evaluation

Core Tests to Order Immediately

• Hemoglobin measurement (preferred over hematocrit due to superior reproducibility and lack of interference from storage time or serum glucose) 1
• Complete blood count including white blood cells, hemoglobin, and platelets to assess overall bone marrow function 1
• Mean corpuscular volume (MCV) to classify anemia type and guide further workup 3, 2
• Reticulocyte count (absolute or adjusted for degree of anemia) to evaluate bone marrow response appropriateness 1, 4

Critical Pattern Recognition

If abnormalities appear in two or more cell lines (white cells, red cells, platelets), immediately consult hematology as this suggests primary bone marrow pathology rather than isolated anemia 1

Classification by MCV and Next Steps

Microcytic Anemia (Low MCV)

• Order iron panel immediately: serum ferritin, transferrin saturation, serum iron, and total iron-binding capacity 1, 3
• Low ferritin indicates absolute iron deficiency and warrants gastrointestinal evaluation for occult bleeding, particularly in older adults 1, 5
• Consider inherited hemoglobin synthesis disorders if iron studies are normal 1

Normocytic Anemia (Normal MCV)

• Check serum ferritin first - functional iron deficiency can present with normal MCV 5
• Evaluate for chronic kidney disease (check creatinine and estimated GFR) 1, 6
• Assess for chronic inflammation or infection (consider inflammatory markers) 7, 2
• Low reticulocyte count with normal iron/folate/B12 suggests erythropoietin deficiency or inflammation 1

Macrocytic Anemia (High MCV)

• Measure vitamin B12 and folate levels 3, 5
• Consider myelodysplastic syndrome evaluation, especially in older adults 5
• Assess for medications causing macrocytosis 2
• Check lactate dehydrogenase, haptoglobin, and bilirubin if hemolysis suspected 3

Peripheral Blood Smear Examination

Order a peripheral smear when: 4

• The diagnosis remains unclear after initial testing
• Red cell morphology may provide diagnostic clues
• Hemolysis is suspected
• Bone marrow pathology is a consideration

Special Populations Requiring Adjusted Thresholds

Standard hemoglobin cutoffs may not apply in: 1

• Pregnant or menstruating women
• Individuals living at high altitude
• Smokers
• Men aged ≥70 years
• Non-Caucasian populations
• Patients with chronic lung disease
• Those with hemoglobinopathies

Frequency of Monitoring

• Screen all chronic kidney disease patients at minimum yearly for anemia development 1
• Diabetic patients require more frequent monitoring due to higher anemia prevalence at earlier CKD stages 1
• Adjust frequency based on underlying conditions and treatment status 6

Red Flags Requiring Urgent Action

• Hemoglobin ≤8 g/dL with symptoms warrants consideration of blood transfusion 5
• Pancytopenia (low counts in multiple cell lines) requires immediate hematology referral 1
• Iron deficiency in older adults mandates endoscopy to exclude gastrointestinal malignancy 5
• Unexplained iron deficiency without menstrual losses requires careful gastrointestinal bleeding assessment 1

Common Pitfalls to Avoid

• Do not rely on hematocrit alone - hemoglobin is more reproducible and accurate 1
• Do not assume CKD is the sole cause of anemia in kidney disease patients - evaluate for other contributing factors 1
• Do not overlook functional iron deficiency - it can occur even with normal or elevated ferritin in inflammatory states 7
• Do not skip fecal occult blood testing when iron deficiency is identified 2