Anemia: Iron Deficiency, B12/Folate Deficiency, and Hemolytic Anemias

Anemia is defined as a reduction in red blood cell mass or hemoglobin concentration below normal values, typically <12 g/dL in women and <13 g/dL in men. The three major categories covered here represent distinct pathophysiologic mechanisms.

Iron Deficiency Anemia (IDA) is the most common form of anemia worldwide, resulting from inadequate iron availability for hemoglobin synthesis. [HIGH_YIELD] Iron stores are depleted in sequence: storage iron (ferritin), transport iron (transferrin saturation), and finally functional iron (hemoglobin). The pathophysiology involves decreased iron absorption, increased iron loss (typically gastrointestinal or menstrual bleeding), or increased iron requirements (pregnancy, growth).

Megaloblastic Anemia from B12 or folate deficiency results from impaired DNA synthesis while RNA synthesis continues normally, leading to large, immature red blood cells. [KEY_CONCEPT] Vitamin B12 (cobalamin) deficiency commonly stems from pernicious anemia (autoimmune destruction of intrinsic factor), while folate deficiency typically results from poor dietary intake or malabsorption.

Hemolytic Anemias encompass disorders causing premature red blood cell destruction, either intravascular or extravascular. [CLINICAL_PEARL] The bone marrow compensates with increased erythropoiesis, evidenced by reticulocytosis and elevated indirect bilirubin. Hemolytic anemias can be inherited (membrane defects, hemoglobinopathies) or acquired (autoimmune, microangiopathic, drug-induced).

General Anemia Symptoms are common across all types and include fatigue, weakness, dyspnea on exertion, and pallor. [HIGH_YIELD] The severity correlates with the degree of anemia and rapidity of onset.

Iron Deficiency Anemia presents with characteristic features beyond general anemia symptoms:

• Koilonychia (spoon-shaped nails)
• Pica (craving for non-food items like ice, starch, or dirt)
• Restless leg syndrome
• Heavy menstrual bleeding in women of reproductive age
• Gastrointestinal symptoms if underlying GI pathology

[CLINICAL_PEARL] In pregnancy, iron deficiency anemia is extremely common due to increased maternal blood volume and fetal iron demands [2].

B12/Folate Deficiency manifests with:

• Neurologic symptoms (B12 only): peripheral neuropathy, subacute combined degeneration of the spinal cord, cognitive impairment
• Glossitis and angular cheilitis
• Gastrointestinal symptoms: diarrhea, anorexia
• Psychiatric symptoms: depression, irritability

Hemolytic Anemias present with:

• Jaundice from elevated indirect bilirubin
• Dark urine (hemoglobinuria in intravascular hemolysis)
• Splenomegaly in extravascular hemolysis
• Gallstones from chronic bilirubin elevation
• Leg ulcers (particularly in sickle cell disease)

[KEY_CONCEPT] Microangiopathic hemolytic anemia (MAHA) presents as part of thrombotic microangiopathies like TTP, characterized by thrombocytopenia, schistocytes, and organ dysfunction [1][3].

Initial Laboratory Evaluation should include complete blood count with differential, reticulocyte count, peripheral blood smear, and basic metabolic panel.

Anemia Diagnostic Algorithm:

1. Confirm anemia (Hgb <12 g/dL women, <13 g/dL men) ↓

2. Assess MCV (Mean Corpuscular Volume) ├─ Microcytic (MCV <80 fL) │ ├─ Check iron studies, TIBC, ferritin │ ├─ Consider thalassemia, chronic disease │ └─ Rule out GI bleeding source ├─ Macrocytic (MCV >100 fL) │ ├─ Check B12, folate levels │ ├─ Assess for hypersegmented neutrophils │ └─ Consider thyroid function, alcohol use └─ Normocytic (MCV 80-100 fL) ├─ Check reticulocyte count ├─ High: suspect hemolysis or bleeding └─ Low: bone marrow disorder

3. If hemolysis suspected: ├─ Check LDH, haptoglobin, indirect bilirubin ├─ Examine peripheral smear for schistocytes └─ Consider direct antiglobulin test (DAT)

Iron Deficiency Criteria:

• ☐ Ferritin <30 ng/mL (or <100 ng/mL with inflammation)
• ☐ Transferrin saturation <16%
• ☐ Elevated total iron-binding capacity (TIBC)
• ☐ Microcytic, hypochromic RBCs
• ☐ Elevated platelet count (reactive thrombocytosis)

Megaloblastic Anemia Criteria:

• ☐ MCV >100 fL
• ☐ Hypersegmented neutrophils (>5% with ≥6 lobes)
• ☐ Oval macrocytes on peripheral smear
• ☐ B12 <200 pg/mL or folate <2 ng/mL
• ☐ Elevated methylmalonic acid (B12 deficiency)
• ☐ Elevated homocysteine (both B12 and folate)

Hemolytic Anemia Criteria:

• ☐ Reticulocyte count >2% (corrected)
• ☐ Elevated LDH (>250 U/L)
• ☐ Decreased haptoglobin (<40 mg/dL)
• ☐ Elevated indirect bilirubin
• ☐ Presence of schistocytes or spherocytes

[HIGH_YIELD] In thrombotic microangiopathies, the combination of thrombocytopenia, microangiopathic hemolytic anemia, and organ dysfunction requires immediate recognition [1][3].

Iron Deficiency Anemia Management:

[CLINICAL_PEARL] Always investigate the underlying cause, especially GI bleeding in men and postmenopausal women.

Oral Iron Therapy:

• First-line treatment: ferrous sulfate 325mg TID (65mg elemental iron per tablet)
• Take on empty stomach with vitamin C to enhance absorption
• Expect hemoglobin rise of 1-2 g/dL over 3-4 weeks
• Continue for 3-6 months after normalization to replete stores

Intravenous Iron Indications:

• Intolerance to oral iron
• Malabsorption
• Severe anemia requiring rapid correction
• Chronic kidney disease
• Heart failure

B12/Folate Deficiency Management:

B12 Deficiency:

• Severe deficiency: 1000 mcg IM daily × 7 days, then weekly × 4 weeks, then monthly
• Maintenance: 1000 mcg IM monthly or high-dose oral B12 (1000-2000 mcg daily)
• [KEY_CONCEPT] Neurologic symptoms may be irreversible if treatment is delayed >6 months

Folate Deficiency:

• Folic acid 1-5 mg daily orally
• Treat underlying cause (malnutrition, malabsorption, alcoholism)
• [HIGH_YIELD] Always check B12 before treating isolated folate deficiency to avoid masking B12 deficiency

Hemolytic Anemia Management:

Thrombotic Microangiopathy Management [1][3]:

• TTP: Immediate plasma exchange, corticosteroids, caplacizumab
• Monitor ADAMTS13 activity and inhibitor levels
• Consider rituximab for relapse prevention

Supportive Care [5]:

• Transfusion for symptomatic anemia or Hgb <7 g/dL
• Iron chelation if transfusion-dependent
• Folic acid supplementation in chronic hemolysis

Iron Deficiency Anemia Complications:

• Cardiac complications: high-output heart failure in severe cases
• Pregnancy complications: preterm delivery, low birth weight [2]
• Cognitive impairment in children and adults
• Restless leg syndrome and sleep disturbances
• Increased infection risk due to impaired immune function

Monitoring:

• Hemoglobin and ferritin levels at 4-6 week intervals
• Continue iron therapy 3-6 months after normalization
• Investigate persistent or recurrent IDA for underlying pathology

B12/Folate Deficiency Complications:

• Irreversible neurologic damage if B12 deficiency untreated >6 months
• Subacute combined degeneration of spinal cord
• Hyperhomocysteinemia increasing cardiovascular risk
• Neural tube defects in pregnancy with folate deficiency
• Pancytopenia in severe megaloblastic anemia

Monitoring:

• B12/folate levels normalize within weeks of treatment
• Neurologic symptoms may take months to improve
• Monitor for relapse if underlying cause not addressed

Hemolytic Anemia Complications:

• Gallstone formation from chronic hyperbilirubinemia
• Pulmonary hypertension in chronic hemolysis (sickle cell, thalassemia)
• Iron overload from chronic transfusions
• Aplastic crisis from parvovirus B19 infection
• Acute kidney injury from intravascular hemolysis

[HIGH_YIELD] Thrombotic Microangiopathy Complications [1][3]:

• Neurologic sequelae (seizures, stroke, cognitive impairment)
• Acute kidney injury requiring dialysis
• Cardiac complications (heart failure, myocardial infarction)
• Relapse risk: 30-50% within 10 years for acquired TTP

Emergency Complications Requiring Immediate Intervention:

• TTP with neurologic symptoms: plasma exchange within 4-8 hours [3]
• Severe anemia with cardiac compromise: urgent transfusion
• Acute intravascular hemolysis with AKI: aggressive hydration, alkalinization

[CLINICAL_PEARL] Regular monitoring is essential as patients with chronic hemolytic conditions require lifelong surveillance for complications including organ damage and malignancy risk.

Iron Deficiency Anemia Prognosis:

• Excellent with appropriate treatment and correction of underlying cause
• Hemoglobin typically normalizes within 6-8 weeks of iron therapy
• [KEY_CONCEPT] Recurrence is common if underlying cause not addressed
• In pregnancy, iron deficiency anemia significantly impacts maternal and fetal outcomes if untreated [2]

Prevention Strategies:

• Dietary counseling: iron-rich foods (red meat, leafy greens, fortified cereals)
• Iron supplementation in high-risk groups (pregnant women, vegetarians)
• Treatment of underlying conditions (heavy menstrual bleeding, GI pathology)

B12/Folate Deficiency Prognosis:

• B12 deficiency: Hematologic abnormalities reverse completely; neurologic damage may be permanent
• Folate deficiency: Excellent prognosis with complete recovery expected
• [HIGH_YIELD] Early recognition and treatment crucial for preventing irreversible complications

Prevention:

• Adequate dietary intake or supplementation in high-risk groups
• Folate supplementation in pregnancy (400-800 mcg daily)
• B12 monitoring in patients with gastrectomy or strict vegetarian diets

Hemolytic Anemia Prognosis:

Long-term Outcomes:

• TTP survivors: 10-20% develop chronic kidney disease [3]
• Autoimmune hemolytic anemia: Relapse rate 25-50%
• Chronic hemolysis: Risk of pulmonary hypertension, leg ulcers

Prevention Strategies:

• Vaccination prior to splenectomy (pneumococcal, meningococcal, H. influenzae)
• Genetic counseling for hereditary hemolytic disorders
• Regular monitoring and prophylaxis in high-risk conditions
• Drug avoidance in G6PD deficiency

[CLINICAL_PEARL] Patients with TTP should be counseled about relapse risk and the importance of immediate medical attention for symptoms of recurrence [3]. Rituximab may reduce relapse rates in selected patients.

Quality of Life Considerations:

• Chronic anemia significantly impacts functional status and cognitive performance
• Patient education crucial for medication adherence and recognition of complications
• Multidisciplinary approach often required for complex hemolytic disorders