What is the Transferrin Saturation (TSAT) for a patient with a serum iron level of 32.5 umol/L and a transferrin level of 2.53 g/L?

Calculating Transferrin Saturation (TSAT)

The transferrin saturation (TSAT) for a patient with serum iron of 32.5 μmol/L and transferrin of 2.53 g/L is 51.4%.

Calculation Method

To calculate TSAT, we need to follow these steps:

• TSAT is calculated by dividing serum iron concentration by total iron-binding capacity (TIBC) and multiplying by 100 1:

  TSAT (%) = (serum iron / TIBC) × 100

• Since we have transferrin concentration (2.53 g/L) rather than TIBC, we need to convert transferrin to TIBC 1:

  • Each transferrin molecule contains two binding sites for iron
  • TIBC can be derived from transferrin using the formula:

    TIBC (μmol/L) = Transferrin (g/L) × 25.1

  • Therefore, TIBC = 2.53 g/L × 25.1 = 63.5 μmol/L

• Now we can calculate TSAT:

  TSAT (%) = (32.5 μmol/L / 63.5 μmol/L) × 100 = 51.4%

Clinical Interpretation

• A TSAT of 51.4% indicates that approximately half of the transferrin binding sites are occupied by iron 1

• Normal TSAT range in adults is typically 20-50% 1

• This patient's TSAT of 51.4% is slightly elevated, suggesting adequate or potentially excessive iron availability for erythropoiesis 1

Clinical Significance of TSAT

• TSAT reflects iron that is readily available for erythropoiesis 1

• Low TSAT (<20%) is often used to confirm iron deficiency 1

• High TSAT (>50%) may indicate iron overload conditions 1

• TSAT is an indicator of iron-deficient erythropoiesis rather than iron depletion; hence, it is less sensitive to changes in iron stores than serum ferritin concentration 1

• TSAT has been shown to have prognostic significance in certain conditions like heart failure, with low TSAT (<20%) associated with worse outcomes 2, 3

Factors Affecting TSAT Measurement

• Diurnal variation: serum iron concentration rises in the morning and falls at night 1

• Recent meals: serum iron concentration increases after meals 1

• Inflammation and infection: can decrease serum iron concentration 1

• Day-to-day variation within individuals is greater for TSAT than for hemoglobin concentration 1

• Other conditions affecting TIBC: inflammation, chronic infection, malignancies, liver disease, nephrotic syndrome, malnutrition (lower TIBC); oral contraceptive use and pregnancy (raise TIBC) 1