What does a low iron saturation and high iron binding capacity indicate?

Low Iron Saturation and High Iron Binding Capacity Indicates Iron Deficiency

A low iron saturation of 13% and high iron binding capacity strongly indicates iron deficiency, which requires further evaluation and appropriate treatment to prevent progression to iron deficiency anemia.

Understanding Iron Saturation and TIBC

• Transferrin saturation (TSAT) indicates the extent to which transferrin has vacant iron-binding sites; a low TSAT indicates a high proportion of vacant iron-binding sites 1
• TSAT is calculated by dividing serum iron concentration by total iron-binding capacity (TIBC) and multiplying by 100 to express the result as a percentage 1
• TIBC is a measure of the iron-binding capacity within the serum and reflects the availability of iron-binding sites on transferrin 1
• TIBC increases when serum iron concentration and stored iron are low 1

Diagnostic Significance

• A TSAT of less than 16% among adults is often used to confirm iron deficiency 1
• Your TSAT of 13% is below this threshold, strongly suggesting iron deficiency 1, 2
• High TIBC further supports the diagnosis of iron deficiency, as it indicates increased production of transferrin to compensate for low iron levels 1
• This pattern (low TSAT + high TIBC) is a classic laboratory finding in iron deficiency 3

Clinical Implications

• Iron deficiency can progress from low iron stores (non-anemic iron deficiency) to iron-deficiency anemia if left untreated 3
• Even without anemia, iron deficiency can cause symptoms such as fatigue, irritability, depression, difficulty concentrating, restless legs syndrome, and pica 3
• Iron deficiency affects approximately 2 billion people worldwide and 14% of adults in the US 3

Common Causes to Investigate

• Bleeding (menstrual, gastrointestinal) is the most common cause of iron deficiency 3
• Other causes include impaired iron absorption (atrophic gastritis, celiac disease, bariatric surgery), inadequate dietary iron intake, and pregnancy 3
• Chronic inflammatory conditions such as inflammatory bowel disease, chronic kidney disease, heart failure, and cancer can also contribute to iron deficiency 3

Next Steps

• Further testing should include serum ferritin measurement, which reflects iron stores 1
• In patients without inflammation, a serum ferritin <30 μg/L confirms iron deficiency 1
• In the presence of inflammation, serum ferritin up to 100 μg/L may still be consistent with iron deficiency 1
• Evaluation for the underlying cause of iron deficiency is essential, particularly to rule out gastrointestinal bleeding in males and non-menstruating females 4

Treatment Considerations

• Oral iron (such as ferrous sulfate 325 mg daily or on alternate days) is typically first-line therapy for most patients 3
• Intravenous iron may be indicated for patients with oral iron intolerance, poor absorption, chronic inflammatory conditions, or ongoing blood loss 3, 5
• Treatment should address both the iron deficiency and its underlying cause 4

Important Caveats

• Several factors can affect TSAT measurement, including diurnal variation, recent meals, inflammation, and infection 2
• Day-to-day variation within individuals is greater for TSAT than for hemoglobin concentration 2
• Do not confuse iron deficiency with anemia of chronic disease, which typically presents with low serum iron, normal TIBC, and normal or high ferritin 4