UIBC from TIBC and Iron Calculator
UIBC from TIBC and Iron Calculator
Derive unsaturated iron binding capacity from TIBC and serum iron, or check that a reported set of iron studies is internally consistent.
UIBC from TIBC and Iron
TIBC − ironTIBC 330 µg/dL, serum iron 95 µg/dL
Formula
TIBC = Serum iron + UIBC
- UIBC
- iron-binding capacity not currently occupied
- units
- all three must be in the same units, normally µg/dL
Worked example
TIBC 330 µg/dL, serum iron 95 µg/dL
330 − 95 = 235 µg/dL
Transferrin saturation = 95 ÷ 330 = 28.8%
The three-way relationship
| Measure | Adult range µg/dL | Iron deficiency | Iron overload |
|---|---|---|---|
| Serum iron | 50 – 175 | Low | High |
| TIBC | 240 – 450 | High | Low or normal |
| UIBC | 155 – 355 | High | Low |
| Saturation | 20 – 45% | < 16% | > 45% |
Using UIBC as a consistency check
Serum iron, TIBC and UIBC are not three independent measurements. TIBC is the sum of the other two, so any two determine the third. Most analysers measure serum iron and UIBC directly, then report TIBC as their sum, which means the arithmetic on a report should be exact rather than approximate.
That makes this calculation useful in two ways. It fills in a missing value when a report quotes only two of the three, which is common when results are transcribed between systems or quoted in a referral letter. And it acts as a check: if the numbers on a report do not add up, something has gone wrong in transcription, or the results come from different samples drawn at different times.
The second use matters more than it might appear. Serum iron changes substantially through the day, so combining an iron from one draw with a TIBC from another produces a saturation that describes no real moment. Confirming that iron plus UIBC equals TIBC is a quick way to be sure the panel came from a single sample.
Frequently asked questions
What is the formula for UIBC?
UIBC = TIBC − serum iron. All three are conventionally reported in µg/dL, and the relationship holds exactly when all three come from the same sample.
My report's numbers do not add up. Why?
Most often the iron and the binding capacity were measured on different samples, or a value was transcribed incorrectly. Serum iron varies enough through the day that mixing draws produces a meaningless saturation.
Which does the laboratory actually measure?
Most analysers measure serum iron and UIBC, then calculate TIBC as the sum. That is why TIBC and UIBC are usually reported together.
Related calculators
References
- Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, iron-binding capacity.
- Camaschella C. Iron deficiency. Blood. 2019;133(1):30–39.