TSAT Calculation
The transferrin saturation (TSAT) is 36.7%, calculated as (133 ÷ 362) × 100, which falls within the normal range of 20-50% and indicates adequate iron availability for erythropoiesis. 1
How to Calculate TSAT
- TSAT (%) = (serum iron / TIBC) × 100 1, 2
- In this case: (133 / 362) × 100 = 36.74%, which rounds to 36.7% 1
Clinical Interpretation of This Result
- This TSAT of 36.7% is normal, as the typical adult range is 20-50% 1
- This value indicates that approximately 37% of transferrin's iron-binding sites are occupied, with 63% remaining vacant 2
- A TSAT ≥20% generally ensures adequate iron for erythropoiesis and suggests the patient does not have iron deficiency 1
What This Result Rules Out
- Iron deficiency is unlikely, as TSAT <16-20% is the threshold used to confirm iron deficiency in most clinical contexts 1, 2
- The patient does not meet criteria for absolute iron deficiency, which requires TSAT <16% in healthy individuals or <20% in those with chronic inflammatory conditions 1
What This Result Does NOT Rule Out
- Transferrin is normally not more than 50% saturated in healthy states, so this value of 36.7% does not suggest iron overload 1
- However, TSAT alone cannot definitively exclude functional iron deficiency in certain populations, particularly those with chronic inflammation, where ferritin levels must also be considered 1
- In chronic kidney disease patients, TIBC may be lower than normal despite iron deficiency, making isolated TSAT interpretation more challenging 1
Important Caveats About TSAT Measurement
- TSAT has significant diurnal variation, rising in the morning and falling at night 1
- Recent meals increase serum iron concentration, which artificially elevates TSAT 1
- Inflammation and infection decrease serum iron, which can falsely lower TSAT 1
- Day-to-day variation in TSAT is greater than for hemoglobin, so a single measurement should be interpreted cautiously 1
When Additional Testing Is Needed
- If evaluating for iron deficiency despite normal TSAT, measure serum ferritin to assess iron stores 2
- Do not evaluate iron parameters within 4 weeks of IV iron administration, as circulating iron interferes with assays 1
- In patients with chronic inflammatory conditions (heart failure, CKD, inflammatory bowel disease), both ferritin and TSAT should be evaluated together, as normal TSAT with low serum iron can still indicate iron deficiency 1, 3