What labs should be ordered for a male patient with iron deficiency anemia secondary to bloody stools?

Laboratory Evaluation for Male with Iron Deficiency Anemia Secondary to Bloody Stools

For a male patient with iron deficiency anemia secondary to bloody stools, comprehensive laboratory testing should include complete blood count with indices, iron studies (ferritin, transferrin saturation, serum iron, TIBC), and non-invasive testing for celiac disease and H. pylori, followed by bidirectional endoscopy. 1, 2

Initial Laboratory Workup

Essential Tests

• Complete blood count (CBC) with:
  • Hemoglobin (Hb < 13 g/dL in men indicates anemia)
  • Red cell indices (MCV, MCH)
  • Red cell distribution width (RDW) - elevated in iron deficiency
  • Reticulocyte count - to assess bone marrow response 1, 2

Iron Studies

• Serum ferritin (most powerful test for iron deficiency)
  • Levels < 45 ng/mL have 85% sensitivity for iron deficiency
  • Levels < 15 ng/mL have 99% specificity but only 59% sensitivity 1, 2
• Transferrin saturation (< 20% indicates iron deficiency)
• Serum iron (typically low in iron deficiency)
• Total iron-binding capacity (TIBC) - typically elevated in iron deficiency 2
• C-reactive protein (CRP) - should accompany ferritin testing to identify inflammatory states that may falsely elevate ferritin 2

Non-Invasive Testing for Common Causes

• Celiac disease serology (anti-tissue transglutaminase antibodies)
• H. pylori testing (stool antigen or urea breath test) 1
• Fecal occult blood test to confirm ongoing bleeding 2

Additional Testing Based on Clinical Context

• If microcytosis and hypochromia are present in patients of appropriate ethnic background:

  • Hemoglobin electrophoresis to rule out hemoglobinopathies 1

• If anemia is severe or there are signs of hemolysis:

  • Lactate dehydrogenase (LDH)
  • Haptoglobin
  • Bilirubin 1

• If chronic kidney disease is suspected:

  • Serum creatinine and eGFR 1, 3

Endoscopic Evaluation

After confirming iron deficiency anemia (Hb < 13 g/dL in men and ferritin < 45 ng/mL):

• Bidirectional endoscopy (both upper and lower GI tract) is strongly recommended for all men with iron deficiency anemia and bloody stools 1
• Colonoscopy is preferred over CT colography for lower GI investigation 1

Interpretation Pitfalls

1. Ferritin interpretation: Ferritin is an acute phase reactant and may be falsely elevated in inflammatory conditions, masking iron deficiency. Always check CRP alongside ferritin 2

2. Normal MCV: Don't rule out iron deficiency based on normal MCV alone, as concurrent B12/folate deficiency or early iron deficiency may result in normocytic anemia 1

3. Incomplete workup: Failing to investigate the underlying cause of iron deficiency is a critical pitfall. In males with bloody stools, gastrointestinal malignancy must be excluded 2

4. Follow-up testing: After treatment initiation, hemoglobin should be rechecked at 4 weeks. Failure to show at least a 1 g/dL increase suggests ongoing bleeding, malabsorption, or non-compliance 2

Monitoring After Diagnosis

• Monitor hemoglobin and ferritin levels 8-10 weeks after treatment initiation
• Once normalized, monitor every 3 months for one year, then annually
• For patients receiving IV iron therapy, check CBC at 3 months post-treatment, then every 3 months for 12 months 2

The laboratory evaluation should be comprehensive but targeted, focusing on confirming iron deficiency, assessing its severity, and identifying the underlying cause of bloody stools, which in males often requires thorough gastrointestinal investigation to rule out malignancy.