Finding the Cause: Why Your Iron is Low

Iron Deficiency Anemia (IDA) is generally a sign that something else is happening in your body ^[1]. While taking iron supplements can improve your blood counts, a critical part of your care is investigating why your iron levels dropped ^[2].

Think of your body’s iron like a bank account: you can become deficient because you are spending too much (blood loss), not depositing enough (poor intake or malabsorption), or because your body has increased its “expenses” (pregnancy or growth) ^[3][4].

Where is the Iron Going?

The search for the cause of IDA typically focuses on several main categories:

• Chronic Blood Loss: This is a leading cause of IDA. In menstruating individuals, heavy menstrual bleeding is a major driver ^[4]. In men and postmenopausal women, the focus shifts to the gastrointestinal (GI) tract ^[5]. Hidden bleeding can occur from stomach ulcers, gastritis, NSAID or anticoagulant use, or polyps and tumors in the colon ^[6][7]. Other sources include urinary tract bleeding or frequent blood donation.
• Malabsorption: Sometimes you consume enough iron, but your body cannot absorb it. This often happens in celiac disease, where the immune system damages the lining of the small intestine ^[8]. It can also occur after gastric bypass surgery or due to an infection with H. pylori, a common bacteria in the stomach ^[9][10].
• Increased Demand or Poor Intake: Your body requires more iron during pregnancy and childhood growth ^[3]. Highly restrictive diets can also fall short of providing the necessary iron.

The Diagnostic Workup: What to Expect

Current clinical guidelines recommend a tailored approach to find the source of the deficiency, depending on your age, symptoms, and risk factors ^[5].

Gastrointestinal Endoscopy

For men and postmenopausal women with confirmed IDA, GI evaluation is typically recommended, often involving a bidirectional endoscopy ^[5][2]. This involves two procedures:

1. Upper Endoscopy (EGD): A camera examines your esophagus and stomach for signs of ulcers, inflammation, or H. pylori (if biopsies are taken) ^[2].
2. Colonoscopy: A camera examines the large intestine (colon) to rule out polyps or colorectal cancer ^[5].

Finding a GI cause does not necessarily mean cancer; ulcers, gastritis, and benign polyps are common culprits. For premenopausal individuals, the decision to undergo endoscopy involves shared decision-making with a doctor, balancing factors like menstrual history, family history of GI disease, and abdominal symptoms ^[5].

Specialized Testing

• Celiac Screening: Because celiac disease can cause IDA without any digestive symptoms, a blood test for tTG-IgA antibodies is often recommended ^[11][8]. Important: You must generally be eating a diet containing gluten for this test to be accurate. The test should also ideally include a “total IgA” check, because being deficient in IgA can cause a false negative result.
• H. Pylori Testing: If initial tests don’t find a cause, your doctor may test for an H. pylori infection. This can often be done noninvasively (via a breath or stool test) ^[10]. Note that proton pump inhibitors (PPIs), antibiotics, and bismuth can interfere with some H. pylori tests.
• Small Bowel Evaluation: If the EGD and colonoscopy are normal but anemia persists, a doctor may recommend a capsule endoscopy (swallowing a pill-sized camera) to examine the middle section of the digestive tract ^[12].

Why Stool Blood Tests Don’t Replace Scopes

You may be familiar with the Fecal Occult Blood Test (FOBT) or FIT test, which checks for hidden blood in your stool. While these are excellent for routine colon cancer screening, they do not replace an endoscopy when an endoscopy is clinically indicated for investigating IDA ^[13]. Many bleeding sources are intermittent, meaning a single stool test can be negative even if a physical cause exists ^[13].