What are the investigations for anemia?

Laboratory Investigations for Anemia

All patients with anemia require a complete blood count (CBC) with red cell indices, absolute reticulocyte count, serum ferritin, and transferrin saturation as the essential initial workup. 1

Core Initial Laboratory Tests

The following tests form the foundation of anemia investigation and should be obtained in all patients:

Essential First-Line Tests

• Complete Blood Count (CBC): Must include hemoglobin concentration, red cell indices (MCV, MCH, MCHC), white blood cell count with differential, and platelet count 1

  • Abnormalities in two or more cell lines warrant hematology consultation 1
  • Mean corpuscular volume (MCV) helps classify anemia type, though mean corpuscular hemoglobin (MCH) may be more reliable for detecting iron deficiency 1

• Absolute Reticulocyte Count: Assesses bone marrow response to anemia 1

  • Low count suggests inadequate production (iron deficiency, erythropoietin deficiency, or inflammation) 1
  • High count suggests hemolysis or blood loss with adequate marrow response 2

• Serum Ferritin: The single most powerful test for iron deficiency 1

  • <15 μg/L indicates absent iron stores 1
  • <30 μg/L generally indicates low body iron stores 1
  • However, ferritin is an acute phase reactant and may be falsely elevated with inflammation, malignancy, or liver disease 1
  • In inflammatory states, ferritin <45 μg/L may still indicate iron deficiency 1

• Transferrin Saturation (TSAT): Represents iron available for erythropoiesis 1

  • <30% suggests inadequate iron for red cell production 1
  • Less affected by inflammation than ferritin, making it more reliable in chronic disease 1

Additional Initial Tests Based on Clinical Context

• Vitamin B12 and Folate Levels: Should be measured in all patients with anemia, particularly if MCV is elevated or normal despite suspected iron deficiency 1
  • Combined deficiencies can mask microcytosis 1
  • Red cell distribution width (RDW) may be elevated in combined deficiencies 1

Interpretation Algorithm

For Microcytic Anemia (Low MCV/MCH)

• If ferritin <15-30 μg/L and/or TSAT <30%: Diagnose iron deficiency anemia 1
• If ferritin >100 μg/L: Iron deficiency is almost certainly not present 1
• If microcytosis with normal iron studies: Obtain hemoglobin electrophoresis to exclude thalassemia, particularly in appropriate ethnic backgrounds 1

For Normocytic Anemia

• Check reticulocyte count 1, 2
  • Low reticulocyte count: Consider chronic kidney disease, anemia of chronic disease, bone marrow disorders 1
  • High reticulocyte count: Evaluate for hemolysis or acute blood loss 2

For Macrocytic Anemia

• Measure vitamin B12 and folate levels 1
• Check reticulocyte count to differentiate causes 3

Confirmatory Testing When Diagnosis Unclear

When iron studies are equivocal or conflicting:

• Therapeutic trial of oral iron: A hemoglobin rise ≥10 g/L within 2 weeks is highly suggestive of absolute iron deficiency, even with equivocal iron studies 1
• Bone marrow aspiration: Definitive for confirming true iron deficiency but rarely necessary 1
• Newer markers (where available): Percent hypochromic red blood cells (PHRBC), reticulocyte hemoglobin content (CHr), or serum transferrin receptor may help distinguish functional iron deficiency from anemia of chronic disease 1

Special Considerations

In Chronic Kidney Disease Patients

• Predialysis hemoglobin measurements are preferred, ideally before midweek dialysis 1
• C-reactive protein may help assess whether elevated ferritin reflects inflammation rather than iron stores 1
• Ferritin <25 ng/mL (males) or <11 ng/mL (females) predicts insufficient iron stores in non-dialysis CKD 1

Critical Pitfalls to Avoid

• Do not accept ferritin alone in inflammatory states: Use TSAT or consider therapeutic trial 1
• Do not assume dietary deficiency explains anemia: Full investigation is still required, particularly in men and postmenopausal women where gastrointestinal pathology (including malignancy) must be excluded 1
• Do not overlook combined deficiencies: Normal MCV does not exclude iron deficiency if concurrent B12/folate deficiency exists 1

When to Pursue Further Investigation

Beyond initial laboratory workup, additional investigation is warranted when:

• Iron deficiency is confirmed in men or postmenopausal women: Requires gastrointestinal evaluation (upper endoscopy with small bowel biopsy and colonoscopy or barium enema) to exclude malignancy and celiac disease 1
• Anemia is transfusion-dependent: Consider enteroscopy or angiography 1
• Multiple cell lines are abnormal: Hematology referral for possible bone marrow evaluation 1