Iron deficiency is the most common nutritional deficiency worldwide. In the UK, it affects around 5% of men and 15% of premenopausal women. When the cause is obvious — heavy periods, vegetarian diet, pregnancy — treatment is straightforward. But when iron deficiency doesn't respond to supplements, or when it occurs in men or postmenopausal women without an obvious explanation, it can signal an underlying condition that needs imaging to investigate.
Understanding Your Iron Results
| Marker | Normal Range | Iron Deficiency | What It Means |
|---|---|---|---|
| Ferritin | 30–300 µg/L (men), 15–200 µg/L (women) | <15 µg/L (definite), 15–30 (borderline) | Iron stores — most useful single marker |
| Serum Iron | 10–30 µmol/L | <10 µmol/L | Circulating iron — varies throughout the day |
| TIBC | 45–80 µmol/L | >80 µmol/L (raised) | The blood's capacity to carry iron — rises when iron is low |
| Transferrin Saturation | 20–50% | <20% | How much of the iron-carrying capacity is being used |
| Haemoglobin | 130–170 g/L (men), 120–150 g/L (women) | Below lower limit | Anaemia — the end result of prolonged iron deficiency |
Iron Overload (the Opposite Problem)
High ferritin (>300 µg/L in men, >200 µg/L in women) with elevated transferrin saturation (>50%) can indicate haemochromatosis — hereditary iron overload that damages the liver. Liver MRI can directly measure iron content. See our liver enzymes guide.
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View Blood Test Details →When Iron Deficiency Needs Imaging
Iron deficiency needs investigation beyond blood tests when:
Red Flags for GI Bleeding
- Iron deficiency in men or postmenopausal women — The NICE guideline CG172 recommends urgent GI investigation for unexplained iron deficiency anaemia in these groups, as it can be the first sign of bowel cancer.
- Iron deficiency not responding to 3 months of oral supplementation — If ferritin isn't rising despite adequate supplementation, you may be losing iron faster than you're replacing it (occult bleeding).
- GI symptoms alongside iron deficiency — Abdominal pain, change in bowel habit, rectal bleeding, weight loss.
- Low iron with raised inflammatory markers — CRP or ESR elevated alongside iron deficiency could indicate Crohn's disease, coeliac disease, or malignancy.
Which Scan Do You Need?
| Suspected Cause | Recommended Scan | Price |
|---|---|---|
| Small bowel pathology (Crohn's, tumour) | Small Bowel MRI | £399 |
| Liver iron overload (haemochromatosis) | Liver MRI | £299 |
| Abdominal mass or organ pathology | Abdomen MRI | £275 |
| Pelvic mass (women) | Pelvis MRI | £275 |
Note: For suspected colorectal cancer (bowel cancer), colonoscopy is the gold standard investigation — not MRI. MRI is better for small bowel disease (Crohn's) and for staging confirmed cancers. If your GP suspects bowel cancer, they'll refer you for colonoscopy via the 2-week-wait pathway.
Related Guides
- Elevated Liver Enzymes → Liver MRI
- When Blood Tests Suggest You Need a Scan
- High Inflammation Markers → MRI
- MRI Scan Cost by Body Part
- Blood Test Then Scan: Complete Pathway
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