What are the common causes of low iron levels in an adult patient with no significant medical history?

Causes of Low Transferrin Iron (Low Iron Levels)

Primary Causes in Adults Without Significant Medical History

Gastrointestinal blood loss is the leading cause of iron deficiency in men and postmenopausal women, accounting for approximately one-third of cases, with about one-third of these proving to be malignancies. 1, 2

Blood Loss (Most Common)

• Gastrointestinal bleeding is the predominant mechanism in adult males and postmenopausal women, requiring urgent investigation even without GI symptoms 3

  • Colorectal cancer, gastric cancer, peptic ulcer disease 2
  • NSAID-induced mucosal damage (including over-the-counter ibuprofen, naproxen, aspirin that patients often fail to report) 4, 3
  • Angiodysplasia (may be unmasked by anticoagulant/antiplatelet use) 4

• Menstrual blood loss is the most common cause in premenopausal women, affecting 38% with iron deficiency without anemia and 13% with iron deficiency anemia 2, 5

• Other bleeding sources include urinary tract bleeding, epistaxis, and regular blood donation 2, 3

Malabsorption

• Celiac disease accounts for 3-5% of all iron deficiency cases and must be screened in every patient with tissue transglutaminase antibody 2, 4, 3

• Gastric acid suppression from chronic PPI therapy impairs iron absorption through hypochlorhydria 1, 2

• Atrophic gastritis (autoimmune or Helicobacter pylori-related) reduces iron absorption 2, 6

• Previous gastrectomy or bariatric surgery significantly impairs iron absorption 2, 5

• Small bowel pathology including bacterial overgrowth, gut resection/bypass, and small bowel tumors 2

Inadequate Dietary Intake

• Poor dietary iron intake particularly affects individuals of lower socioeconomic status with limited access to iron-rich foods 3

• Vegetarian diets are inherently low in heme iron (the most bioavailable form), though vitamin C co-consumption partially compensates 3

• This alone rarely causes iron deficiency in adult males without other contributing factors 3

Increased Demand

• Pregnancy increases iron requirements, with iron deficiency affecting up to 84% of pregnant women in the third trimester 5

Critical Diagnostic Pitfalls to Avoid

• Do not assume dietary deficiency is the sole cause even with positive dietary history—full GI investigation is still required in adult males 3

• Do not stop investigating after finding one cause, as multiple etiologies coexist in 10-15% of patients 4, 3

• Do not accept minor endoscopic findings (such as small hiatal hernia) as sole explanation without completing lower GI investigation 4, 3

• Failing to screen for celiac disease results in missed diagnoses in 3-5% of cases 4, 3

• Not explicitly asking about over-the-counter NSAID use leads to missed diagnoses, as patients frequently fail to report these medications 4, 3

Essential Initial Workup

• Serum ferritin <15 μg/L is highly specific for iron deficiency (specificity 0.99); ferritin <45 μg/L warrants GI investigation 3

• Celiac disease screening with tissue transglutaminase antibody is mandatory in every case 4, 3

• Urinalysis or urine microscopy should be performed to exclude urinary tract bleeding 2, 3

• Bidirectional endoscopy (gastroscopy with duodenal biopsies and colonoscopy) is required as first-line investigation in all adult males and postmenopausal women, regardless of symptom absence 1, 4, 3