Iron Overload and NTBI
Core Concept
When iron exceeds transferrin binding capacity, toxic circulating species appear:
- NTBI (non-transferrin-bound iron)
- LPI (labile plasma iron, redox-active NTBI fraction)
These species drive oxidative damage and organ injury more directly than ferritin alone.
Why This Matters In Your Labs
- TSAT 60% is in the range where NTBI is often detectable
- Ferritin is still elevated/high-normal at 380 ug/L
- Prior ferritin ~700 suggests substantial prior iron loading
Pathophysiology Summary
- Transferrin saturation rises
- NTBI appears in plasma
- NTBI enters cells via non-regulated pathways
- Iron catalyzes ROS generation (Fenton chemistry)
- Lipid/protein/DNA damage accumulates
Target organs: liver, pancreas, heart, endocrine tissue, joints, possibly CNS.
Colour Key
🔴 Trigger | 🟠Cascade | 🔵 Organ damage | ⚪ Outcome
flowchart TD
TSAT["TSAT rises above 45%"] --> TF_SAT["Transferrin saturated"]
TF_SAT --> NTBI["NTBI appears in plasma"]
NTBI --> UPTAKE["Non-regulated cell uptake"]
UPTAKE --> FENTON["Fenton reaction: Fe2+ + H2O2"]
FENTON --> ROS["ROS generation"]
ROS --> LIVER["Liver damage"]
ROS --> HEART["Cardiac iron loading"]
ROS --> BRAIN["Brain oxidative stress"]
ROS --> JOINTS["Joint cartilage damage"]
ROS --> ENDO["Endocrine disruption"]
ROS --> PANC["Pancreatic beta-cell loss"]
LIVER --> HCC["Fibrosis / HCC risk"]
ENDO --> PITU["Pituitary iron deposition"]
classDef trigger fill:#f1948a,stroke:#c0392b,color:#1a0505
classDef cascade fill:#f1948a,stroke:#c0392b,color:#1a0505
classDef damage fill:#f1948a,stroke:#c0392b,color:#1a0505
classDef outcome fill:#f7dc6f,stroke:#b7950b,color:#1a1400
class TSAT,TF_SAT trigger
class NTBI,UPTAKE,FENTON,ROS cascade
class LIVER,HEART,BRAIN,JOINTS,ENDO,PANC damage
class HCC,PITU outcomeKey Evidence
- Duca L et al. Int J Mol Sci 2025;26(13):6433 - comprehensive NTBI/LPI toxicity review (PMC12249652)
- Garbowski MW et al. Am J Hematol 2023;98(3):533-540 - clinical relevance of plasma iron species in overload states (DOI: 10.1002/ajh.26819)
- Ryan E et al. EJHaem 2022;3(3):644-652 - NTBI can persist in HFE hemochromatosis despite treatment (PMC9422009)
- Silva AMN, Rangel M. Molecules 2022;27:1784 - chemistry and biology of NTBI
- Breuer W et al. Transfus Sci 2000;23(3):185-192 - foundational NTBI work
Practical Implication
In iron overload, ferritin is useful, but TSAT and NTBI-risk physiology are central for toxicity risk. Your persistent TSAT elevation supports ongoing risk despite dietary improvement.