Iron Deficiency: Expected TSAT and TIBC Levels
Direct Answer
In iron deficiency, you should expect TSAT to be LOW and TIBC to be HIGH. 1
Understanding the Laboratory Pattern
Transferrin Saturation (TSAT)
- TSAT is LOW in iron deficiency because there is insufficient iron available to saturate transferrin, the iron transport protein 1, 2
- In absolute iron deficiency, TSAT falls below 20% in CKD patients (or below 16% in healthy individuals) 1
- The lower the TSAT, the higher the likelihood that iron deficiency is present 1
- TSAT reflects iron that is readily available for erythropoiesis 1
Total Iron-Binding Capacity (TIBC)
- TIBC is HIGH in iron deficiency because the body compensates by producing more transferrin to capture whatever iron is available 1
- This represents the body's attempt to maximize iron uptake when stores are depleted
- However, in CKD patients specifically, TIBC may be LOW despite iron deficiency due to malnutrition and inflammation, which suppress transferrin production 3
Special Considerations in CKD Stage 2 Patients
Diagnostic Thresholds
- Absolute iron deficiency in CKD is defined as TSAT <20% AND ferritin <100 ng/mL 1, 2
- These thresholds differ from healthy individuals (TSAT <16%, ferritin <12 ng/mL) 4
- Your patient with CKD stage 2 should be evaluated using the CKD-specific criteria 1
Functional vs. Absolute Iron Deficiency
- Functional iron deficiency occurs when TSAT <20% but ferritin is elevated (>100 ng/mL), indicating adequate stores but insufficient iron release for erythropoiesis 1, 2
- This pattern is common in CKD patients receiving erythropoietin-stimulating agents 1
- Absolute iron deficiency shows both low TSAT (<20%) and low ferritin (<100 ng/mL) 1
Critical Pitfall: TIBC in CKD
A major caveat is that TIBC may be unreliable in CKD patients because:
- Low TIBC (<200 μg/dL) is associated with hypoalbuminemia and elevated C-reactive protein in CKD 3
- Malnutrition and inflammation suppress transferrin production, leading to falsely low TIBC despite true iron deficiency 3
- Therefore, in CKD patients, low serum iron with normal TSAT can still indicate iron deficiency risk when TIBC is suppressed by inflammation 3
Clinical Implications for Your Patient
- Monitor TSAT and ferritin at least every 3 months to optimize iron status 1
- The probability of iron deficiency increases as TSAT and ferritin values decrease 1
- Apixaban use does not directly affect these iron parameters, but any occult bleeding could worsen iron deficiency 1
- Consider that even with "normal" TSAT (>20%), low serum iron (<70 μg/dL in men, <60 μg/dL in women) still confers anemia risk in CKD patients 3