Divide or subtract: transferrin saturation versus unbound iron binding capacity (UIBC)

Area of Science:

• Clinical Chemistry
• Hematology
• Diagnostic Medicine

Background:

• Plasma transferrin saturation (TSAT) is a traditional marker for iron deficiency but is influenced by inflammation.
• Plasma ferritin is a preferred indicator of iron deficiency, yet TSAT is still widely used.
• The behavior of unbound iron binding capacity (UIBC) during inflammation is not well understood.

Purpose of the Study:

• To evaluate the diagnostic accuracy of UIBC and TSAT for iron deficiency.
• To assess the impact of inflammation on UIBC, TSAT, and ferritin levels.
• To compare UIBC and TSAT as indicators of iron deficiency in a large patient cohort.

Main Methods:

• Cross-sectional analysis of data from 21,681 patients.
• Investigation of the relationship between UIBC, TSAT, ferritin, and C-reactive protein (CRP).
• Comparison of diagnostic accuracy using ROC curves with ferritin thresholds (15, 20, 30 µg/L) as reference standards in a non-inflammatory subpopulation (CRP ≤ 1 mg/L).

Main Results:

• UIBC demonstrated significantly less variation with CRP levels compared to TSAT and ferritin.
• UIBC exhibited superior diagnostic accuracy for iron deficiency compared to TSAT (AUC 0.894 vs. 0.850, using ferritin < 20 µg/L).
• UIBC values around 60 µmol/L corresponded to a ferritin level of 20 µg/L, indicating iron deficiency.

Conclusions:

• Calculating UIBC provides a more accurate assessment of iron deficiency than TSAT.
• UIBC is a more robust diagnostic marker for iron deficiency, especially in the presence of inflammation.
• UIBC represents a superior method for utilizing plasma iron and total iron-binding capacity measurements for diagnosing iron deficiency.