Iron studies
Transferrin saturationTSAT
Iron in transit; complements ferritin to discriminate deficiency, overload, and inflammation.
Sample
Serum, fasting morning
Clinical reference range
20 to 50 %
Adult
Conv: 20–50 %Func: 25–35 %
Biology
What it measures
TSAT = (serum iron / TIBC) × 100. Reflects the proportion of transferrin binding sites occupied by Fe(III).
Clinical use
Why we order it
Distinguish iron deficiency (low TSAT, low ferritin) from inflammation (low TSAT, normal/high ferritin) from overload (high TSAT, high ferritin).
Lens · Clinical
Interpretation by lens
Clinical interpretation
TSAT >45% (men) or >40% (women) on two occasions warrants HFE testing.
Functional interpretation
TSAT <20% with normal Hb and ferritin still drives RLS, fatigue, and exercise intolerance — consider treatment.
Differential
Causes of abnormal values
Causes of HIGH
- ↑Hereditary hemochromatosis
- ↑Transfusional iron overload
- ↑Liver disease
- ↑Recent oral iron dose (transient peak — wait 24 h)
Causes of LOW
- ↓Iron deficiency
- ↓Anemia of chronic disease
- ↓Heart failure
- ↓Chronic kidney disease
Pitfalls
Pre-analytic & interpretation traps
- !Diurnal variation: serum iron peaks AM, declines PM — always sample morning fasting.
- !Recent oral or IV iron causes transient TSAT spike; wait 24 h (oral) or 7+ days (IV).
Related