What does a serum unsaturated iron‑binding capacity of 131 µg/dL indicate?

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Last updated: October 5, 2026 • View editorial policy

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Interpretation of Serum UIBC 131 µg/dL

A serum unsaturated iron-binding capacity (UIBC) of 131 µg/dL falls within the normal range and does not indicate iron deficiency, though interpretation must be contextualized with other iron parameters, inflammatory markers, and clinical presentation.

Understanding UIBC Values

UIBC represents the reserve capacity of transferrin to bind additional iron. This value of 131 µg/dL requires interpretation alongside:

  • Serum iron concentration
  • Total iron-binding capacity (TIBC)
  • Transferrin saturation (TSAT)
  • Serum ferritin
  • Inflammatory markers (CRP, ESR)

Clinical Context for Interpretation

Normal Reference Ranges

Research indicates that UIBC values vary by demographic factors 1. In healthy adults, mean values cluster around typical ranges, with this value of 131 µg/dL generally falling within normal limits for most populations.

Iron Deficiency Screening

For detecting iron deficiency, UIBC thresholds of 143-150 µg/dL have been established as optimal cut-points 2, 3. Your value of 131 µg/dL falls below these thresholds, suggesting adequate iron availability rather than deficiency.

  • UIBC >143 µg/dL suggests possible iron deficiency 2
  • UIBC >150 µg/dL (women) or >125 µg/dL (men) indicates likely iron deficiency in hemochromatosis screening 4

Calculating Transferrin Saturation

UIBC is most useful when combined with serum iron to calculate TSAT:

TSAT (%) = [Serum Iron / (Serum Iron + UIBC)] × 100

Critical TSAT thresholds 5, 6, 7:

  • <16%: Indicates iron deficiency (high sensitivity)
  • <20%: Suggests functional iron deficiency, especially in chronic disease 6
  • <30%: May warrant further evaluation 8

Diagnostic Algorithm

Without Inflammation (CRP normal)

If your TSAT calculates to:

  • ≥20%: Iron stores likely adequate
  • <16%: Iron deficiency confirmed if ferritin <30 µg/L 5
  • 16-20%: Borderline; check ferritin

With Inflammation (elevated CRP/ESR)

The interpretation changes significantly 5:

  • Ferritin >100 µg/L + TSAT <16%: Anemia of chronic disease 5
  • Ferritin 30-100 µg/L + TSAT <16%: Mixed iron deficiency and chronic disease 5
  • Ferritin <30 µg/L: True iron deficiency regardless of inflammation 5

Key Clinical Pitfalls

Do not interpret UIBC in isolation. The value of 131 µg/dL appears normal, but without knowing:

  • Your serum iron level (to calculate TSAT)
  • Your ferritin level
  • Your inflammatory status
  • Your clinical context (anemia, chronic disease, symptoms)

A complete assessment is impossible.

UIBC has significant biological variability 4. A single normal value does not exclude iron deficiency if measured at a different time point, particularly in conditions with fluctuating iron metabolism.

Practical Recommendations

For complete iron status assessment, obtain:

  1. Serum ferritin (most specific for iron stores 8, 9, 10)
  2. Complete blood count (hemoglobin, MCV, MCH)
  3. Inflammatory markers (CRP or ESR) 5
  4. Serum iron (to calculate TSAT with your UIBC)

If ferritin <45 µg/L with anemia, consider gastrointestinal evaluation regardless of UIBC 9, 10, as this threshold provides optimal sensitivity-specificity balance for clinically significant iron deficiency.

References

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.