What is the initial hematology consult workup for a patient presenting with iron deficiency anemia?

Initial Hematology Consult Workup for Iron Deficiency Anemia

The minimum initial workup for iron deficiency anemia includes complete blood count with red cell indices (MCV, RDW), reticulocyte count, serum ferritin, transferrin saturation, and CRP, followed by systematic evaluation for underlying causes including gastrointestinal pathology. 1

Diagnostic Confirmation

Laboratory Testing Requirements

Minimum essential tests to establish the diagnosis and guide management: 1

• Complete blood count with differential, including:

  • Hemoglobin (anemia defined as <13 g/dL in men, <12 g/dL in non-pregnant women) 1
  • Mean corpuscular volume (MCV) to assess microcytosis
  • Red cell distribution width (RDW) - elevated in iron deficiency 1
  • White blood cell count and platelet count

• Iron studies:

  • Serum ferritin <45 ng/mL confirms iron deficiency 1
  • Transferrin saturation (TfS) - values <16-20% support iron deficiency 1

• Reticulocyte count - low or inappropriately normal indicates defective erythropoiesis rather than hemolysis 1

• C-reactive protein (CRP) - essential to interpret ferritin in inflammatory states 1

Critical Interpretation Caveat

Ferritin is an acute phase reactant, so interpretation must account for inflammation. 1 In patients with inflammatory conditions, ferritin up to 100 ng/mL may still indicate iron deficiency. 1 When ferritin is 30-100 ng/mL with elevated CRP, consider mixed iron deficiency and anemia of chronic disease. 1

Extended Workup When Indicated

More extensive laboratory evaluation should be performed when: 1

• The cause remains unclear after initial testing
• Macrocytosis is present (MCV elevated)
• Suspicion for combined deficiencies exists

Additional tests include: 1

• Vitamin B12 and folate levels
• Haptoglobin, lactate dehydrogenase, and bilirubin (if hemolysis suspected)
• Percentage of hypochromic red cells
• Reticulocyte hemoglobin content
• Soluble transferrin receptor (helps distinguish iron deficiency from anemia of chronic disease) 1
• Creatinine and urea (assess renal contribution)

Evaluation for Underlying Etiology

Non-Invasive Testing First

Before proceeding to endoscopy, perform: 1

• Non-invasive testing for H. pylori - can cause iron malabsorption and occult bleeding 1, 2
• Celiac disease serologic screening with tissue transglutaminase antibody (IgA) and total IgA level 1, 2

Small bowel biopsies during endoscopy should be reserved for those with positive serology or high clinical suspicion, not performed routinely. 1

Clinical History Priorities

Focus the history on: 1

• Dietary iron intake - identify truly deficient diets, though this alone should not preclude GI investigation 1
• Medication review - NSAIDs, aspirin, anticoagulants (note their use but do not defer investigation) 1
• Menstrual blood loss in premenopausal women 1, 3
• Prior gastrointestinal surgery - gastrectomy, bariatric surgery, bowel resection causing malabsorption 1, 2
• Family history of bleeding disorders or hereditary hematologic conditions 1

Gastrointestinal Evaluation Strategy

Bidirectional endoscopy (upper endoscopy and colonoscopy) is strongly recommended for: 1

• All men with iron deficiency anemia (strong recommendation)
• All postmenopausal women with iron deficiency anemia (strong recommendation)
• Premenopausal women with iron deficiency anemia (conditional recommendation - younger women who prioritize avoiding endoscopy risk over detecting rare malignancy may choose empiric iron supplementation first) 1

Upper endoscopy detects pathology in 30-50% of patients and should include: 1

• Evaluation for peptic ulcer disease, erosive esophagitis, gastric cancer
• Assessment for vascular lesions (angiodysplasia, Cameron lesions)
• Duodenal biopsies even without positive celiac serology if high suspicion remains 1

Colonoscopy or barium enema is required even when upper GI pathology is found, as dual pathology occurs in 10-15% of patients. 1 Do not accept minor findings like esophagitis or gastric erosions as the sole explanation without completing lower GI evaluation. 1

When to Involve Hematology

Hematology consultation is appropriate when: 1

• The cause of anemia remains unclear after comprehensive workup
• Atypical features suggest primary bone marrow disease
• Anemia is refractory to appropriate iron replacement
• Complex mixed anemia patterns exist
• Difficulty accessing intravenous iron therapy 1

Common Pitfalls to Avoid

Do not assume dietary deficiency alone explains iron deficiency anemia without completing GI evaluation, as approximately one-third of men and postmenopausal women have underlying GI pathology, including malignancy. 1

Do not stop anticoagulants or antiplatelet agents to perform investigation - their use should not deter appropriate workup. 1

Do not accept elevated ferritin as excluding iron deficiency in patients with inflammatory conditions - use transferrin saturation and clinical context. 1

Do not perform routine gastric and duodenal biopsies for H. pylori and celiac disease during endoscopy if non-invasive testing was negative and no endoscopic abnormality is present. 1

In patients with unrevealing bidirectional endoscopy who are transfusion-dependent or have ongoing blood loss, consider video capsule endoscopy for small bowel evaluation rather than accepting the diagnosis as unexplained. 1