What is the most common cause of low serum iron in elderly postmenopausal women?

Most Common Cause of Low Blood Iron in Elderly Women

Chronic gastrointestinal blood loss is the most common cause of iron deficiency in elderly postmenopausal women, and both upper endoscopy and colonoscopy must be performed urgently to exclude malignancy. 1, 2

Primary Etiology

The British Society of Gastroenterology explicitly states that while menstrual loss causes iron deficiency in premenopausal women, iron deficiency in postmenopausal women is most often due to chronic blood loss from the gastrointestinal tract. 1 This represents the leading cause until proven otherwise through complete investigation. 2

Gastrointestinal Malignancy Risk

• Colorectal cancer and gastric cancer are the most critical diagnoses to exclude, as asymptomatic malignancies commonly present with iron deficiency anemia in this population. 2
• Iron deficiency may be the first presenting manifestation of colonic or esophago-gastric carcinoma, highlighting the urgency of swift and complete investigation. 1
• Research demonstrates that gastrointestinal malignancy is found in approximately 15-16% of elderly patients with iron deficiency anemia. 3

Other Gastrointestinal Bleeding Sources

• Peptic ulcer disease, erosive gastritis/duodenitis, and angiodysplasia are common upper GI sources of occult bleeding. 2, 4
• Dual pathology (bleeding sources in both upper and lower GI tracts) occurs in 1-10% of patients, with risk increasing with age—this must be particularly considered in older patients. 1, 2
• Colonic polyps and vascular ectasias represent additional lower GI bleeding sources. 5

Secondary Causes (Non-Bleeding)

Malabsorption Disorders

• Celiac disease is found in 3-5% of all iron deficiency anemia cases and must be screened for serologically in every postmenopausal woman with iron deficiency. 2
• Atrophic gastritis is a frequently overlooked cause, found in a substantial proportion of patients without overt bleeding. 5
• Helicobacter pylori gastritis should be eradicated if present in patients with recurrent iron deficiency and normal endoscopy. 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. 2
• Patients often don't consider over-the-counter medications worth mentioning, making explicit questioning essential. 2

Other Contributing Factors

• Poor dietary iron intake, particularly in patients of lower socioeconomic status with limited access to iron-rich foods. 2
• Prior GI or bariatric surgery involving the stomach and/or small bowel. 1
• Urinary tract bleeding (must be excluded with urinalysis in all cases). 2

Mandatory Diagnostic Algorithm

Initial Confirmation

• Serum ferritin <15 μg/L is highly specific for iron deficiency (specificity 0.99); ferritin <45 μg/L warrants GI investigation. 2
• Red cell indices provide sensitive indication of iron deficiency in the absence of chronic disease. 1

Required Investigations

All postmenopausal women with confirmed iron deficiency must undergo:

1. Both upper endoscopy (with duodenal biopsies) AND colonoscopy as first-line investigations—this is non-negotiable. 1, 2
2. Celiac disease screening with tissue transglutaminase antibody or duodenal biopsies during gastroscopy. 2
3. Urinalysis or urine microscopy to exclude urinary tract bleeding. 2

Endoscopic Priorities

• Upper endoscopy with duodenal biopsies evaluates for gastric cancer, peptic ulcer disease, celiac disease, and angiodysplasia. 2
• Colonoscopy is preferred over CT colonography to exclude colorectal cancer and polyps; CT colonography is acceptable only if colonoscopy is not feasible. 1, 2
• Only the presence of advanced gastric cancer or celiac disease should deter lower GI investigation if upper endoscopy is performed first. 1

Critical Pitfalls to Avoid

• Never assume dietary deficiency or NSAID use is the sole cause without completing full bidirectional endoscopy—malignancy must be excluded. 1, 2
• Fecal occult blood testing is of no benefit in the investigation of iron deficiency anemia and should not guide decision-making. 1
• Site-specific symptoms and positive fecal occult blood tests are not reliable predictors of gastrointestinal lesions and should not determine investigation strategy. 4
• Do not stop investigating after finding one benign cause—dual pathology occurs in up to 10% of cases, and synchronous colonic tumors are found in 9.5% of patients with benign upper GI lesions. 4