What is the difference between ferritin and serum iron levels?

From the Guidelines

Ferritin is the preferred test for assessing iron status compared to serum iron, as it provides a more accurate reflection of total body iron stores. When evaluating for iron deficiency or overload, ordering ferritin rather than serum iron is recommended because ferritin levels are less affected by daily fluctuations and external factors such as recent meals, medications, and acute inflammation 1. Ferritin is an intracellular protein that stores iron and releases it in a controlled manner, with normal levels typically ranging from 20-250 ng/mL for men and 10-120 ng/mL for women.

Key differences between ferritin and serum iron levels:

• Ferritin reflects storage iron, whereas serum iron measures circulating iron bound to transferrin.
• Ferritin is a more stable and reliable indicator of iron status, while serum iron levels can fluctuate significantly throughout the day.
• Ferritin functions as an acute phase reactant, increasing during inflammation or infection, which must be considered when interpreting results.

Clinical implications:

• For comprehensive iron status assessment, ferritin should be evaluated alongside other markers like transferrin saturation, total iron binding capacity (TIBC), and complete blood count, particularly in complex cases where both iron deficiency and chronic inflammation may coexist 1.
• A low level of serum ferritin may indicate the need for supplemental iron to support erythropoiesis, while a high level may suggest iron overload 1.
• The British Society of Gastroenterology guidelines recommend confirming iron deficiency by iron studies prior to investigation, with serum ferritin being the single most useful marker of iron deficiency anaemia 1.

From the FDA Drug Label

Inclusion criteria prior to randomization included hemoglobin (Hb) <12 g/dL, ferritin ≤100 ng/mL or ferritin ≤300 ng/mL when transferrin saturation (TSAT) ≤30%. Iron deficiency was defined as serum ferritin <100 ng/mL or 100 to 300 ng/mL with TSAT <20%.

The difference between ferritin and serum iron levels is that:

• Ferritin is a protein that stores iron in the body, and low levels of ferritin indicate iron deficiency.
• Serum iron levels refer to the amount of iron in the blood, but the label does not provide a direct comparison or difference between the two. 2

From the Research

Difference between Ferritin and Serum Iron Levels

• Ferritin and serum iron levels are two different measures used to assess iron status in the body 3, 4.
• Serum ferritin reflects the stored iron in the body, while serum iron measures the amount of iron in the blood that is available for use by the body 4, 5.
• Serum ferritin is considered a more reliable indicator of iron stores, as it is less affected by daily fluctuations in iron intake and other factors 4, 6.
• Serum iron levels, on the other hand, can be influenced by various factors such as inflammation, infection, and recent iron intake, making them a less reliable measure of iron status 5, 7.

Diagnostic Criteria

• Iron deficiency is typically diagnosed based on a combination of clinical evaluation, laboratory tests, and medical history 3, 5.
• Serum ferritin levels are often used as a diagnostic criterion, with levels below 100 μg/L indicating iron deficiency in patients with chronic heart failure 6.
• Transferrin saturation (TSAT) is also used as a diagnostic criterion, with levels below 20% indicating iron deficiency 6, 7.
• The use of serum ferritin levels alone as a diagnostic criterion may not be sufficient, as inflammation and other conditions can affect ferritin levels 7.

Clinical Implications

• Accurate diagnosis of iron deficiency is crucial, as it can have significant clinical implications, particularly in patients with chronic diseases such as heart failure and inflammatory bowel disease 6, 7.
• Iron deficiency can be treated with oral or intravenous iron supplementation, depending on the severity of the deficiency and the patient's medical history 3, 5.
• Regular monitoring of serum ferritin and TSAT levels is recommended in high-risk groups, such as patients with chronic diseases, to detect and manage iron deficiency early 7.