What level of transferrin saturation indicates iron deficiency anemia?

Transferrin Saturation Levels Indicating Iron Deficiency Anemia

A transferrin saturation (TSAT) less than 16-20% is the diagnostic threshold for iron deficiency anemia in most clinical contexts. 1

Diagnostic Criteria for Iron Deficiency Anemia

• In healthy individuals without inflammation, a TSAT below 16% indicates absolute iron deficiency 2, 1
• In patients with chronic inflammatory conditions, TSAT below 20% is typically used as the diagnostic threshold 2
• Serum ferritin should be evaluated alongside TSAT for accurate diagnosis:
  • Ferritin <30 ng/mL with low TSAT confirms absolute iron deficiency in non-inflammatory states 2, 3
  • In inflammatory conditions, ferritin up to 100 ng/mL may still indicate iron deficiency despite elevated levels 2

Context-Specific Diagnostic Thresholds

Chronic Kidney Disease (CKD)

• Absolute iron deficiency in CKD is defined as:
  • TSAT ≤20% and serum ferritin ≤100 ng/mL in pre-dialysis and peritoneal dialysis patients 4
  • TSAT ≤20% and serum ferritin ≤200 ng/mL in hemodialysis patients 4
• Functional iron deficiency in CKD: TSAT ≤20% with elevated ferritin levels 2, 4

Heart Failure

• TSAT <20% is considered diagnostic for iron deficiency in heart failure patients 2, 5
• Low serum iron concentration may be more strongly associated with anemia and mortality than TSAT in heart failure patients 5

Inflammatory Bowel Disease

• TSAT <20% with ferritin 30-100 μg/L suggests a combination of true iron deficiency and anemia of chronic disease 2

Limitations of TSAT as a Diagnostic Marker

• TSAT has significant diurnal variation (higher in morning, lower at night) 1
• Recent meals can increase serum iron concentration and affect TSAT 1
• Inflammation decreases serum iron concentration, potentially falsely lowering TSAT 1, 6
• Day-to-day variation in TSAT is greater than hemoglobin variation 1
• Low total iron binding capacity (TIBC) due to malnutrition or inflammation may result in falsely normal TSAT despite iron deficiency 6

Clinical Implications

• Patients with normal TSAT but low serum iron may still be at risk for anemia, particularly in CKD 6
• In inflammatory states, TSAT may not accurately reflect iron status due to changes in transferrin concentration 5
• Laboratory evaluation following IV iron therapy should include TSAT measurement 4-8 weeks after the last infusion 1
• A goal TSAT of ≥20% is generally desired to ensure adequate iron for erythropoiesis 1

Common Pitfalls in Diagnosis

• Relying solely on TSAT without considering ferritin levels may lead to missed diagnoses 2
• Failing to account for inflammatory status when interpreting TSAT and ferritin 2
• Not recognizing that functional iron deficiency can occur despite normal or elevated ferritin levels 2, 4
• Measuring iron parameters within 4 weeks of IV iron administration can interfere with accurate assessment 1