Understanding Your Iron Blood Tests: A Patient Guide
What These Tests Tell Us About Your Iron Levels
Your doctor has ordered several blood tests to check your iron status. Here's what each one means and how they work together:
Ferritin
Ferritin measures your iron storage—think of it as your body's iron savings account. 1
- Normal levels: Men typically have 69 ng/mL, women around 35 ng/mL 2
- Low ferritin (<10-30 ng/mL): Your iron stores are depleted—this is iron deficiency 2, 1
- High ferritin (>300 ng/mL): Can mean iron overload, but more commonly indicates inflammation, liver disease, infection, or other conditions 3, 4
Important caveat: Ferritin rises during any inflammation, infection, or liver disease, even when you're actually iron deficient. This makes it tricky to interpret on its own. 4, 1
Serum Iron
This measures the iron currently circulating in your bloodstream—like the cash in your wallet. 5
- This number fluctuates throughout the day and with recent meals 1
- Low serum iron can indicate iron deficiency or inflammation 5
- It's less reliable than other tests when used alone 5
Transferrin and TIBC (Total Iron Binding Capacity)
Transferrin is the protein that carries iron through your blood. TIBC measures how much iron your blood can carry total. 1
- High TIBC/transferrin: Your body is trying to grab more iron because stores are low 5
- Low TIBC/transferrin: Often seen with inflammation or liver disease 4
- TIBC is calculated from transferrin levels 1
Transferrin Saturation (Iron Saturation)
This is the percentage of transferrin proteins that are actually carrying iron—the most important test for detecting true iron overload. 1
- Calculated as: (Serum Iron ÷ TIBC) × 100 1
- Normal range: 20-50% 4, 6
- Low (<20%): Indicates iron deficiency or that iron is trapped by inflammation 4, 6
- High (≥45%): Suggests possible iron overload and may require genetic testing for hemochromatosis 1, 7
What Different Patterns Mean
Pattern 1: True Iron Deficiency
- Low ferritin (<30 ng/mL)
- Low serum iron
- High TIBC/transferrin
- Low transferrin saturation (<20%)
What this means: Your iron stores are depleted and your body needs iron. 4, 1
Pattern 2: Anemia of Inflammation (Inflammatory Iron Block)
- High or normal ferritin (>100 ng/mL)
- Low serum iron
- Low or normal TIBC
- Low transferrin saturation (<20%)
What this means: You have iron stored, but inflammation is preventing your body from using it. Iron supplements won't help until the underlying inflammation is treated. 3, 4, 7
Pattern 3: Iron Overload
- High ferritin (>300 ng/mL)
- High serum iron
- Normal or low TIBC
- High transferrin saturation (≥45%)
What this means: You may have too much iron in your body, which requires further evaluation for conditions like hemochromatosis. 1, 7
Pattern 4: Functional Iron Deficiency
- Ferritin 100-700 ng/mL
- Low transferrin saturation (<20%)
What this means: You have stored iron, but it's not getting to where it needs to go fast enough. This can occur in chronic kidney disease or heart failure. 4, 6, 7
How Iron Deficiency Is Treated
Oral Iron Supplements
For true iron deficiency (low ferritin, low transferrin saturation), your doctor will typically prescribe ferrous sulfate 300 mg three times daily. 7
- Take for at least 3 months to fully replenish stores, not just until you feel better 7
- Target: Ferritin >100 ng/mL and transferrin saturation >20% 6, 7
- Common side effects: Constipation, nausea, dark stools 3
- Recheck blood tests after 3 months of treatment 1, 7
Intravenous (IV) Iron
IV iron may be needed if: 1, 3
- You can't tolerate oral iron due to side effects
- You have inflammatory bowel disease or other absorption problems
- Oral iron hasn't worked after 3 months
- You have chronic kidney disease or heart failure with functional iron deficiency
- You need rapid iron replacement
Available IV iron formulations include iron sucrose, ferric carboxymaltose, and iron dextran. 3
Important Testing Guidelines
Before Your Blood Draw
For accurate results, avoid all iron supplements and iron-rich foods for 24 hours before testing. Get your blood drawn in the morning. 7
Foods to avoid: 7
- Iron supplements
- Iron-fortified cereals
- Red meat
- Organ meats
- Shellfish
After Treatment
- Don't recheck iron tests within 4 weeks of IV iron—it interferes with the results 1
- Hemoglobin should increase by 1-2 g/dL within 4-8 weeks of treatment 1
- Continue treatment until ferritin reaches >100 ng/mL, even if you feel better 7
When to Seek Further Evaluation
Your doctor should investigate further if: 7
- You have iron deficiency without an obvious cause (especially if over age 50)
- Your ferritin is very high (>1000 ng/mL) with high transferrin saturation
- You have ongoing blood loss
- Iron supplements aren't working after 3 months
The most important thing to remember: Transferrin saturation is the key test that distinguishes true iron overload from other causes of high ferritin. Never rely on ferritin alone. 1, 7