What are the possible etiologies of anemia when hemolysis and overt bleeding are absent?

Anemia Without Hemolysis or Bleeding: Etiologies

When hemolysis and overt bleeding are excluded, anemia is most commonly caused by iron deficiency (including occult GI losses), nutritional deficiencies (B12/folate), chronic kidney disease, anemia of chronic disease/inflammation, or bone marrow disorders.

Systematic Approach by MCV Classification

Microcytic Anemia (MCV <80 fL)

Iron deficiency remains the primary consideration even without obvious bleeding:

• Occult GI blood loss - Upper GI cancer occurs in 1/7 the frequency of colon cancer in iron deficiency anemia patients 1
• Iron malabsorption - Atrophic gastritis, celiac disease, chronic inflammation, post-bariatric surgery 2, 1
• Genetic disorders of iron metabolism - Consider when ferritin is elevated/normal (>20 μg/L) with low transferrin saturation, or family history of refractory anemia 3
• Thalassemia syndromes 3
• Anemia of chronic disease (severe cases) 3

Critical pitfall: In inflammatory conditions (IBD, CHF), ferritin up to 100 μg/L may still represent iron deficiency due to acute phase reactant elevation 2. Check transferrin saturation in these cases.

Normocytic Anemia (MCV 80-100 fL)

The differential broadens significantly 4:

• Anemia of inflammation/chronic disease - Most common normocytic cause
• Chronic kidney disease - Impaired erythropoietin production 4
• Endocrine disorders - Hypothyroidism, hypopituitarism 5
• Early nutritional deficiencies - Before MCV elevation occurs
• Bone marrow disorders - Aplastic anemia, myelodysplasia, marrow infiltration 4
• Acute blood loss - Before equilibration (initially normocytic) 4

Macrocytic Anemia (MCV >98 fL)

Without hemolysis, consider:

• Vitamin B12 deficiency - Including pernicious anemia (can present with pseudo-hemolytic picture: elevated LDH, indirect bilirubin, low haptoglobin, but inappropriately low reticulocyte count) 6
• Folate deficiency 3
• Alcohol toxicity 3
• Myelodysplastic syndrome 3
• Medications - Chemotherapy, antiretrovirals, anticonvulsants

Specific High-Risk Populations

Chronic Heart Failure

40-70% have iron deficiency (ferritin <100 μg/L and/or transferrin saturation <20%) due to malabsorption, malnutrition, chronic inflammation with elevated hepcidin 2

Inflammatory Bowel Disease

One-third have iron deficiency; ferritin up to 100 μg/L may still indicate deficiency in active inflammation 2

Post-GI Surgery

Common after gastric/small bowel resection or bariatric surgery, but do not assume this is the sole cause - still investigate for other etiologies 2

Diagnostic Algorithm

For unexplained iron deficiency anemia without overt bleeding 1:

1. Serological celiac screening - Transglutaminase antibody (IgA) plus total IgA
2. Bidirectional endoscopy (gastroscopy + colonoscopy) - Exception: premenopausal women <40 years may not require this
3. Small bowel investigation (capsule endoscopy, CT/MRI enterography) - Only if red flags present: weight loss, abdominal pain, elevated CRP

For normocytic anemia 4, 5:

1. Assess renal function (creatinine, eGFR)
2. Inflammatory markers (CRP, ESR)
3. Thyroid function
4. Reticulocyte count (to assess marrow response)
5. Peripheral smear examination
6. Consider bone marrow evaluation if above unrevealing

Critical Caveat

Pseudo-hemolytic presentation: Severe B12 deficiency can mimic hemolysis with elevated LDH, indirect bilirubin, and low haptoglobin, but the reticulocyte count will be inappropriately low and DAT negative 6. This represents ineffective erythropoiesis, not true hemolysis - check B12 levels before pursuing hemolysis workup aggressively.