Serum ferritin is a blood measurement that shows how much iron your body has in storage. Ferritin itself is a protein that binds to iron and holds it inside your cells, releasing it when your body needs more. When a doctor orders a ferritin test, they’re measuring the small amount of this protein that circulates in your bloodstream, which reliably reflects the larger reserves tucked away in your liver, bone marrow, and other tissues.
What Ferritin Tells You That Other Iron Tests Don’t
A ferritin test is often ordered alongside other iron-related blood work, and it’s easy to confuse them. A serum iron test measures how much iron is floating in your blood right now. A total iron-binding capacity (TIBC) test measures how much transferrin, a transport protein made by your liver, is available to carry iron through your bloodstream. Ferritin is different from both: it measures stored iron, not circulating iron or transport capacity.
Of the three, ferritin is the better marker for assessing iron deficiency. Serum iron fluctuates throughout the day and after meals, while ferritin gives a more stable picture of your overall iron status. That said, ferritin has its own quirks that can make interpretation tricky, which is why doctors sometimes order a full iron panel rather than relying on any single number.
Normal Ferritin Ranges
According to the Mayo Clinic, typical blood ferritin levels are:
- Men: 24 to 336 micrograms per liter (µg/L)
- Women: 11 to 307 µg/L
That’s a wide range, and where you fall within it matters. A ferritin level below 15 µg/L is widely used as the cutoff for depleted iron stores. The World Health Organization uses 12 µg/L for children under five and 15 µg/L for everyone older. During pregnancy, levels below 30 µg/L are considered early iron depletion and typically prompt treatment, since the body’s iron demands increase significantly.
What Low Ferritin Feels Like
Low ferritin doesn’t always mean you’re anemic. Iron deficiency exists on a spectrum: your stored iron can drop well before your red blood cell counts fall low enough to qualify as anemia on a standard blood test. This in-between state, sometimes called iron deficiency without anemia, is common and often overlooked.
Even mild iron depletion, with ferritin levels below 20 to 35 µg/L, can cause real symptoms. The most common is fatigue that doesn’t improve with rest. Other signs include reduced exercise tolerance, difficulty concentrating or thinking clearly, restless legs (an uncomfortable urge to move your legs, especially at night), and poor sleep quality. These symptoms are frustratingly nonspecific, which is why they’re easy to dismiss or attribute to stress, poor sleep habits, or aging. If you’re experiencing persistent fatigue and your doctor hasn’t checked ferritin specifically, it’s worth requesting.
Common Causes of Low Ferritin
Low ferritin means your body is using iron faster than it’s taking it in, or it’s losing iron somewhere. The most frequent causes include heavy menstrual periods, pregnancy, not getting enough iron from food (common in vegetarians and vegans), and conditions that reduce iron absorption like celiac disease or inflammatory bowel disease. Blood loss you can’t see, such as slow bleeding from a stomach ulcer or colon polyp, is another important cause, particularly in men and postmenopausal women who don’t have an obvious explanation for iron loss.
What High Ferritin Can Mean
Elevated ferritin doesn’t always mean you have too much iron. This is one of the most important things to understand about the test. Ferritin is what’s called an acute phase reactant, meaning your liver pumps out more of it whenever there’s inflammation, infection, or tissue damage in your body. Signals from your immune system directly stimulate ferritin production, independent of your actual iron levels. The result: your ferritin reading can look normal or even high while your true iron stores are low.
This matters practically. If you’re fighting an infection, dealing with a flare of an autoimmune condition, or have chronic inflammation from any cause, a ferritin result can be misleading. The WHO recommends that in the presence of infection or chronic disease, ferritin levels between 30 and 100 µg/L may actually indicate depleted iron stores, even though those numbers would look perfectly normal on a standard lab report. Doctors sometimes order an additional inflammation marker, like C-reactive protein (CRP), alongside ferritin to help sort out whether an elevated reading reflects true iron excess or just inflammation.
When ferritin is genuinely elevated due to excess iron, the list of possible causes is long. It includes:
- Hemochromatosis: a genetic condition causing excessive iron absorption. Genetic testing is recommended when ferritin exceeds 300 µg/L in men or 200 µg/L in women, along with elevated transferrin saturation above 45%.
- Liver disease: both alcoholic and nonalcoholic fatty liver disease raise ferritin.
- Heavy alcohol use
- Chronic kidney disease
- Blood disorders: including thalassemia, sickle cell anemia, and conditions requiring frequent blood transfusions
- Metabolic syndrome
- Infections: viral hepatitis, HIV, and others
Extremely high levels, above 10,000 µg/L, narrow the possibilities and typically point to serious conditions like advanced liver dysfunction, certain cancers, or rare inflammatory diseases in acutely ill patients.
Ferritin During Pregnancy
Pregnancy deserves its own mention because the rules change. Blood volume increases dramatically, diluting ferritin concentrations, while the growing baby draws heavily on maternal iron stores. British haematology guidelines consider ferritin below 15 µg/L diagnostic of established iron deficiency at any stage of pregnancy. But treatment is recommended at the higher threshold of 30 µg/L, because waiting until stores are fully depleted makes catching up much harder. Women at increased risk of iron depletion, including those with known blood disorders, are typically screened with ferritin early in pregnancy.
How the Test Works
A ferritin test is a simple blood draw, no different from any other routine lab work. Your provider may ask you to fast beforehand, particularly if ferritin is being ordered as part of a full iron panel that includes a serum iron test (which is more sensitive to recent food intake). The ferritin measurement itself isn’t significantly affected by a recent meal, but follow whatever preparation instructions your lab provides.
Results usually come back within a day or two. If your level falls outside the normal range, your doctor will likely consider it alongside your complete blood count, serum iron, transferrin saturation, and your symptoms before deciding on next steps. A single ferritin number rarely tells the whole story on its own, but it’s one of the most useful starting points for understanding your body’s iron status.