Iron Deficiency Anemia

Detailed Overview

Iron is an essential component of the heme molecule in hemoglobin, which carries oxygen to tissues. When iron stores are depleted (due to bleeding, malabsorption, or poor diet), the bone marrow produces smaller, less pigmented red blood cells. In adult men and postmenopausal women, IDA must be considered a sign of occult gastrointestinal malignancy until proven otherwise.

Epidemiology & Demographics

Affects over 1.2 billion people globally. Most common in women of childbearing age (menorrhagia) and young children in developing nations.

Etiological Mechanism

Blood loss (overt or occult), inadequate dietary intake, decreased intestinal absorption, or increased physiologic demand (pregnancy).

Primary Causes

Menorrhagia (heavy menstrual bleeding) - most common cause in premenopausal women

Gastrointestinal bleeding (peptic ulcers, NSAID use, colon cancer) - most common cause in adult men

Malabsorption (Celiac disease, post-gastric bypass surgery)

Pregnancy and lactation (increased demand)

• Menstruating women: Regular blood loss rapidly depletes iron stores.
• Vegan/Vegetarian diet: Lacks highly bioavailable heme iron found in meat.
• Frequent blood donation: Removes 200-250 mg of iron per pint.

Iron balance is tightly regulated by absorption in the duodenum, controlled by the hormone hepcidin. There is no excretory pathway for iron; loss occurs only through bleeding or mucosal sloughing. When losses exceed absorption, iron stores (ferritin) are first depleted. Next, serum iron falls and transferrin (TIBC) increases. Finally, the bone marrow lacks iron to synthesize heme. Erythropoiesis is impaired, resulting in a microcytic (low MCV), hypochromic anemia.

Characteristic Clinical Presentation

• Fatigue and Weakness: Due to decreased oxygen delivery to tissues.
• Pica: Unusual cravings for non-nutritive substances like ice (pagophagia), dirt, or clay.
• Restless Legs Syndrome: Urge to move the legs, especially at night, strongly linked to low CNS iron.
• Dyspnea on exertion: Shortness of breath during physical activity.

Physical Examination Signs

• Pallor of the conjunctivae, palmar creases, and nail beds
• Koilonychia (spoon-shaped, brittle nails) - rare, seen in chronic severe IDA
• Glossitis (smooth, red, painful tongue)
• Angular cheilitis (fissures at the corners of the mouth)

• Plummer-Vinson Syndrome: Triad of IDA, esophageal webs, and dysphagia; carries a risk of squamous cell carcinoma.
• Heart Failure: Chronic severe anemia forces a high cardiac output state, leading to left ventricular hypertrophy and failure.
• Developmental delay: Severe IDA in infants can cause irreversible cognitive and motor deficits.

Diagnostic Criteria & Guidelines

Microcytic anemia (Low Hgb, Low MCV < 80 fL) confirmed by low serum ferritin (<30 ng/mL is diagnostic, <15 ng/mL is highly specific), low serum iron, and elevated Total Iron Binding Capacity (TIBC).

Differential Diagnosis

• Thalassemia trait
• Anemia of Chronic Disease (Inflammation)
• Sideroblastic Anemia
• Lead poisoning

Laboratory Tests & Biomarkers

• Serum Ferritin: Low (< 30 ng/mL). The most accurate initial test. Note: Ferritin is an acute-phase reactant and can be falsely normal in inflammation.
• Total Iron Binding Capacity (TIBC): Elevated (reflecting liver producing more transferrin to grab available iron).
• Transferrin Saturation: Low (< 15-20%). Calculated as Serum Iron / TIBC.
• Complete Blood Count: Low Hemoglobin, Low MCV, High RDW (Red Cell Distribution Width).

Imaging Modalities & Findings

• Endoscopy/Colonoscopy: Not diagnostic for the anemia itself, but MANDATORY in adult men and postmenopausal women with IDA to locate the source of GI bleeding (e.g., colon cancer, ulcers).

• Iron Depletion
  Low ferritin, normal hemoglobin, normal MCV. Asymptomatic.
• Iron Deficient Erythropoiesis
  Low ferritin, low serum iron, high TIBC. Hemoglobin is low-normal, MCV starts dropping.
• Overt Anemia
  Low hemoglobin, low MCV (microcytic), marked hypochromasia. Symptomatic.

Second-Line & Adjunctive Therapy

Intravenous (IV) Iron (e.g., Iron Sucrose 200 mg IV per dose, or Ferric carboxymaltose 750 mg IV). Indicated for patients intolerant to oral iron (severe GI distress), severe malabsorption (gastric bypass, active IBD), or requiring rapid correction (severe anemia in late pregnancy).

Surgical & Procedural Management

Surgery is directed entirely at the underlying cause (e.g., colon resection for cancer, hysterectomy for fibroids causing intractable menorrhagia).

Recommended Lifestyle Changes

• Increase dietary intake of heme iron (red meat, poultry, fish) which is better absorbed than non-heme iron (spinach, lentils).
• Avoid drinking tea or milk with iron-rich meals (tannins and calcium block absorption).
• Cook with cast-iron cookware.

Patient Counseling & Advice

Warn patients that oral iron will turn their stools black or dark green (normal side effect) and can cause constipation, requiring over-the-counter stool softeners.

Follow-Up & Monitoring Schedule

Recheck CBC and reticulocyte count in 2-4 weeks. Reticulocytes should peak in 7-10 days. Hemoglobin should increase by 1 g/dL every 2-3 weeks. Continue iron therapy for 3-6 months AFTER hemoglobin normalizes to replenish ferritin stores.

Preventive Strategies

Prophylactic iron supplementation in pregnancy. Universal screening for infants at 9-12 months. Treating underlying bleeding disorders.

Excellent with proper supplementation and identification of the root cause. Failure to respond usually indicates non-compliance, continued unrecognized bleeding, or an incorrect diagnosis.