What are the common causes of iron deficiency anemia (IDA) in a postmenopausal woman?

Causes of Iron Deficiency Anemia in Postmenopausal Women

In postmenopausal women with iron deficiency anemia, gastrointestinal blood loss is the primary cause and must be assumed until proven otherwise, requiring both upper endoscopy and colonoscopy to exclude malignancy. 1

Primary Gastrointestinal Causes

Malignant Lesions

• Colorectal cancer and gastric cancer are the most critical diagnoses to exclude, as asymptomatic malignancies commonly present with IDA in this population 1, 2
• Dual pathology (bleeding sources in both upper and lower GI tracts) occurs in 1-10% of patients, with risk increasing with age 1
• Age, hemoglobin concentration, and mean cell volume are independent predictors of GI cancer risk and must be considered in holistic risk assessment 1

Benign Upper GI Lesions

• Peptic ulcer disease and erosive esophagitis are frequent causes of occult blood loss 3, 4
• Gastric angiodysplasia and arteriovenous malformations cause chronic bleeding 3
• Helicobacter pylori gastritis should be eradicated if present in patients with recurrent IDA and normal endoscopy 1

Benign Lower GI Lesions

• Colonic polyps and diverticulosis are common sources of chronic blood loss 3, 4
• Angiodysplasia of the colon, particularly in elderly patients 2

Malabsorption Disorders

Celiac Disease

• Celiac disease is found in 3-5% of all IDA cases and must be screened for serologically in every postmenopausal woman with IDA 1
• Screen with tissue transglutaminase antibody or obtain small bowel biopsies during gastroscopy 1
• The threshold for investigation should be low even without GI symptoms 1

Other Malabsorption Causes

• Bacterial overgrowth, particularly after gastrectomy 1
• Inflammatory bowel disease (Crohn's disease affecting small bowel) 2

Medication-Induced Blood Loss

• NSAID use (including over-the-counter ibuprofen, naproxen, aspirin) is a common and frequently unreported cause of GI mucosal damage and occult bleeding 1, 5
• Anticoagulants and antiplatelet agents can unmask underlying vascular lesions 5
• Explicitly ask about all NSAID use, as patients often don't consider over-the-counter medications worth mentioning 5

Non-Gastrointestinal Causes

Genitourinary Blood Loss

• Urinalysis or urine microscopy should be performed in all cases to exclude urinary tract bleeding 1
• Hematuria from bladder lesions or chronic urinary tract pathology 5

Nutritional Deficiency

• Poor dietary iron intake, particularly in patients of lower socioeconomic status with limited access to iron-rich foods 5
• However, dietary deficiency alone is uncommon in developed countries and should not be assumed without completing full GI investigation 1, 2

Chronic Disease States

• Chronic kidney disease causing both decreased erythropoietin production and functional iron deficiency 6
• Chronic inflammatory conditions (heart failure, rheumatologic diseases) causing functional iron deficiency 6

Mandatory Diagnostic Algorithm

The British Society of Gastroenterology provides clear guidance for postmenopausal women: 1

1. Confirm iron deficiency: Serum ferritin <15 μg/L is highly specific (specificity 0.99); ferritin <45 μg/L warrants GI investigation 1

2. Initial investigations must include: 1

   • Urinalysis or urine microscopy
   • Celiac disease screening (tissue transglutaminase antibody)
   • Both gastroscopy AND colonoscopy as first-line investigations

3. Upper endoscopy with duodenal biopsies to evaluate for gastric cancer, peptic ulcer disease, celiac disease, and angiodysplasia 1

4. Colonoscopy is preferred over CT colonography to exclude colorectal cancer and polyps; CT colonography is acceptable only if colonoscopy is not feasible 1

5. Do not stop after finding one lesion: Complete both upper and lower GI investigations even if an upper GI source is identified, unless advanced gastric cancer or celiac disease is found 1

Critical Pitfalls to Avoid

• Never assume dietary deficiency or minor findings are the sole cause without completing full bidirectional endoscopy 1, 2
• Fecal occult blood testing is of no benefit in the investigation of IDA and should not be used for risk stratification 1
• Do not defer investigation based on absence of GI symptoms, as most patients with significant GI pathology are asymptomatic 3, 4
• Failing to screen for celiac disease results in missed diagnoses in 3-5% of cases 1
• Not asking specifically about over-the-counter NSAID use leads to missed medication-induced causes 5