What additional labs are recommended for patients presenting with anemia?

Additional Laboratory Tests for Anemia Evaluation

When evaluating a patient with anemia, a comprehensive laboratory workup should include complete blood count with indices, reticulocyte count, serum ferritin, transferrin saturation, and C-reactive protein as the minimum initial tests. 1

Initial Laboratory Assessment

• Complete Blood Count (CBC) including:

  • Hemoglobin concentration
  • Red cell indices (MCV, MCH, MCHC)
  • Red cell distribution width (RDW)
  • White blood cell count and differential
  • Platelet count

• Reticulocyte count - critical for distinguishing between production defects and blood loss/hemolysis 1, 2

• Iron studies:

  • Serum ferritin
  • Transferrin saturation (TSAT)
  • Consider soluble transferrin receptor in inflammatory states 1

• Inflammatory marker: C-reactive protein (CRP) 1

Additional Testing Based on Initial Results

For Microcytic Anemia (MCV <80 fL)

• Serum iron
• Total iron binding capacity
• Hemoglobin electrophoresis (if thalassemia suspected)
• Lead levels (particularly in children)

For Normocytic Anemia (MCV 80-100 fL)

• Renal function tests (BUN, creatinine)
• Liver function tests
• Thyroid function tests
• Lactate dehydrogenase (LDH)
• Haptoglobin (if hemolysis suspected)
• Direct antiglobulin test (Coombs test) for immune hemolysis 1

For Macrocytic Anemia (MCV >100 fL)

• Vitamin B12 level
• Folate level
• Methylmalonic acid (more sensitive for B12 deficiency)
• Homocysteine level
• Liver function tests
• Thyroid function tests
• Reticulocyte hemoglobin content 1

Special Considerations

For Suspected Bone Marrow Disorders

• Peripheral blood smear examination
• Bone marrow aspiration and biopsy (if myelodysplastic syndrome or aplastic anemia suspected)

For Suspected Gastrointestinal Blood Loss

• Fecal occult blood testing
• Non-invasive testing for H. pylori and celiac disease before endoscopy 1

For Suspected Chronic Disease/Inflammation

• When ferritin is 30-100 ng/mL with low TSAT (<20%), consider combination of true iron deficiency and anemia of chronic disease 1
• Percentage of hypochromic red cells may help distinguish 1

For Inadequate Response to Iron Therapy

• Consider evaluation for additional causes of anemia 1, 2
• Small bowel evaluation (capsule endoscopy or CT/MR enterography) 2

Monitoring Response to Therapy

• Check hemoglobin response within 4 weeks of starting iron therapy 2
• Expected rise in hemoglobin is approximately 2 g/dL after 3-4 weeks 2
• Monitor hemoglobin and MCV at 3-month intervals for one year, then again at 2 years 2

Important Pitfalls to Avoid

• Don't rely solely on MCV for classification: Concurrent conditions can mask typical MCV changes (e.g., iron deficiency with B12 deficiency can result in normal MCV)
• Don't overlook inflammation: Ferritin is an acute phase reactant; levels up to 100 ng/mL may still indicate iron deficiency in inflammatory states 1
• Don't assume minor GI findings explain significant anemia: Hemorrhoids or diverticulosis are often incidental and not the cause of significant iron deficiency anemia 2
• Don't stop at negative bidirectional endoscopy: Up to 30-50% of patients with iron deficiency anemia have upper GI sources of blood loss, and small bowel pathology may be present in those with negative initial evaluation 2

By following this systematic approach to laboratory testing in anemia, clinicians can efficiently identify the underlying cause and implement appropriate treatment to improve patient outcomes.