What are the possible causes of anemia in an obese 35‑year‑old woman?

Causes of Anemia in an Obese 35-Year-Old Woman

In an obese 35-year-old woman, anemia is most commonly caused by menstrual blood loss, but obesity itself creates a chronic inflammatory state that impairs iron metabolism and causes functional iron deficiency, making this population uniquely susceptible to both iron deficiency anemia and anemia of chronic disease. 1, 2

Primary Causes Specific to This Population

Menstrual Blood Loss

• Menstrual blood loss remains the most common cause of iron deficiency anemia in premenopausal women, including those who are obese 3
• Heavy menstrual bleeding (menorrhagia) can deplete iron stores even before anemia develops 3

Obesity-Related Anemia of Chronic Disease

• Obesity induces chronic low-grade inflammation that activates the immune system and disrupts iron homeostasis, leading to hypoferremia, iron-restricted erythropoiesis, and mild-to-moderate anemia 1, 2
• This inflammatory state causes iron to be trapped in enterocytes and macrophages as a defense mechanism, making it unavailable for erythropoiesis despite adequate total body iron stores 2, 4
• Anemia of chronic disease accounts for approximately 43.8% of anemia cases in obese patients preoperatively 1
• The prevalence of anemia is substantially higher among overweight/obese females compared to normal-weight individuals 5

Compromised Iron Absorption

• Obesity-related inflammation impairs dietary iron absorption at the enterocyte level 2, 4
• Inflammatory conditions, including obesity, result in iron being retained in enterocytes and macrophages, causing hypoferremia 4

Other Important Causes to Consider

Gastrointestinal Pathology

• Gastrointestinal bleeding from mucosal lesions is a critical cause that must be excluded, particularly from NSAID use, colon cancer/polyps, gastric cancer, or angiodysplasia 3, 6
• NSAID use is a common cause of occult GI blood loss 3

Malabsorption

• Celiac disease occurs in 3-5% of patients with iron deficiency anemia and must be routinely screened for 3, 6
• Poor dietary intake of iron-rich foods is common in obesity despite overall caloric excess 3

Chronic Kidney Disease

• CKD should be considered if GFR is <60 mL/min/1.73m², as it causes multifactorial anemia including functional iron deficiency 3

Diagnostic Approach

Initial Laboratory Assessment

• Serum ferritin <30 μg/L indicates iron deficiency in healthy individuals, but in obesity-related inflammation, use a threshold of <100 μg/L 3
• Transferrin saturation <20% supports iron deficiency diagnosis 6
• Ferritin acts as an acute phase reactant and can be falsely elevated in the inflammatory state of obesity, making interpretation challenging 3

Mandatory Screening

• Screen for celiac disease with tissue transglutaminase antibody (IgA) and total IgA levels 3, 7
• Urinalysis to exclude urinary blood loss 3
• Assess renal function (GFR) to identify chronic kidney disease 3

When to Pursue GI Investigation

• If the patient is approaching menopause or has GI symptoms, family history of GI pathology, or inadequate response to iron supplementation, proceed with bidirectional endoscopy (gastroscopy and colonoscopy) 3, 7
• Age, hemoglobin concentration, and mean cell volume are independent predictors of GI cancer risk and should guide investigation intensity 3

Critical Clinical Pitfalls

• Multiple causes frequently coexist in obese patients (e.g., menstrual loss plus obesity-related inflammation plus celiac disease), so finding one explanation should not stop further investigation if anemia persists 7
• Mild anemia is not less significant than severe anemia as an indicator of serious disease 6
• A history of poor diet should not preclude thorough investigation for GI pathology 6
• The inflammatory state of obesity can mask true iron deficiency by elevating ferritin levels, requiring use of higher ferritin thresholds for diagnosis 3, 2