Health Reference LibraryFerritin blood test results explained: what does your number mean?
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
Reading a UK ferritin result takes five thresholds. Below 15 µg/L is iron deficiency by WHO standards; below 30 confirms it in UK NICE-aligned practice; above 50 excludes it in healthy adults; up to 70 it can hide behind inflammation; and raised results, with evaluation flagged above 500 in non-healthy adults, are usually inflammation, liver or alcohol rather than iron overload. Every band on that scale behaves differently by sex, life stage and symptoms, which is why each has its own page below, and why a single number is only ever the start of the reading.
Free iron and ferritin result interpreter
Enter what you have. Your ferritin alone works; the other fields sharpen the reading. Nothing you enter leaves this device. Nothing is saved. No AI is used, only published UK guideline thresholds.
This tool gives educational interpretation of published evidence. It is not personal dosing advice and it does not diagnose. It knows nothing about your history, symptoms or other results. Interpreting your results over time, alongside everything else about you, is what Nutri365 does.
How it works
Ferritin is the protein iron is stored in, and the serum test reads how much reserve you hold, which is why it falls before haemoglobin does and rises again last during recovery. Two properties shape every interpretation. First, it is a store gauge, not a supply gauge, so a normal blood count can coexist with empty stores, the common and commonly missed state of non-anaemic iron deficiency. Second, it is an acute-phase protein: infection, inflammation, liver strain and alcohol all raise it independent of iron, which is why a CRP alongside makes any borderline or raised result far more readable.
Timing
The rhythm of iron is slow and worth internalising: haemoglobin responds inside 4 weeks, symptoms lift across the first one to two months, stores rebuild over months with the honest ferritin retest at 8 to 12 weeks, and repletion continues 3 months past resolution. Raised results run a different clock, a repeat with CRP and liver tests when well, and trend established over months. The single most useful habit at any band is keeping your results with their dates, because the trend outreads any snapshot.
Safety profile
Three rules stand at every band. Red flags, blood in stool or black stools, unexplained weight loss, swallowing difficulty, persistent abdominal pain, mean GP first at any ferritin. Deficient results in men and post-menopausal women need their cause found, not just their number corrected. And iron supplements are contraindicated in haemochromatosis, have no place at replete or raised levels, and must be stored away from children at every level.
Special populations
The same number reads differently across people, which is what the band pages unpack. Menstruating women run lower distributions and drain faster, so borderline numbers carry trend weight. Men and post-menopausal women at deficient levels always raise the cause question, most often gastrointestinal. Pregnancy moves the action line to 30 on NHS maternity pathways and accelerates demand through the trimesters. Athletes underperform at levels general practice calls fine, and sports literature works to higher comfort zones. Chronic inflammatory conditions shift every threshold and belong with the clinical team reading them.
Guideline positions
WHO 2020: deficiency below 15 µg/L in apparently healthy adults, below 12 in under-fives, deficiency possible up to 70 with infection or inflammation, and evaluation indicated above 500 in non-healthy adults. UK NICE-aligned practice: below 30 confirms deficiency at 92 percent sensitivity and 98 percent specificity, below 40 reaches 98 percent on both, above 50 excludes deficiency absent inflammation, with a 4-week blood count recheck after starting iron and repletion continuing 3 months past resolution. Chronic-condition guidance in heart failure, kidney disease and IBD reads ferritin below 100 alongside transferrin saturation.
Practical framework
Find your band and read its page: [below 8](/apps/learn/ferritin-5-below-8-what-severe-depletion-means), [8 to 12](/apps/learn/ferritin-10-what-does-a-result-under-12-mean), [13 to 15](/apps/learn/ferritin-15-is-that-low-and-what-should-you-do), [16 to 20](/apps/learn/ferritin-18-is-that-low-or-normal), [21 to 30](/apps/learn/ferritin-25-is-that-low-or-borderline), [31 to 45](/apps/learn/ferritin-35-what-low-normal-stores-mean), [46 to 70](/apps/learn/ferritin-60-deficiency-excluded-what-it-means), [71 to 100](/apps/learn/ferritin-85-comfortably-normal-stores), [101 to 150](/apps/learn/ferritin-120-mid-normal-range), [151 to 300](/apps/learn/ferritin-200-normal-or-raised), [above 300](/apps/learn/ferritin-400-raised-what-needs-checking). Where correction is indicated, the pattern is constant: cause considered, iron-rich food with vitamin C pairing, [Iron & Vitamin C](/products/iron-vitamin-c) on alternate days where a supplement is warranted, ferritin retested at 8 to 12 weeks, and the [repletion timeline](/apps/learn/iron-supplementation-timeline-symptom-resolution-ferritin-normalisation) setting honest expectations.
Ferritin thresholds at a glance (UK, µg/L)
| Threshold | Meaning | Source |
|---|---|---|
| Below 15 | Iron deficiency in apparently healthy adults | WHO 2020 |
| Below 30 | Iron deficiency confirmed in UK practice (92% sensitivity, 98% specificity) | NICE CKS / NHS |
| Below 40 | Deficiency highly likely (98% sensitivity and specificity) | NHS guidance |
| Above 50 | Deficiency excluded, unless inflammation is present | NHS guidance |
| Below 70 with inflammation | Deficiency still possible when CRP is raised | WHO 2020 |
| Above 500 | Possible overload or other disease, needs clinical evaluation | WHO 2020 |
Sources
- 2020. WHO guideline on use of ferritin concentrations to assess iron status. World Health Organization.
- 2024. Iron deficiency guidelines. NHS Scotland Right Decisions.
- 2023. Ferritin interpretation, a guide for GPs. Royal United Hospitals NHS (NICE CKS aligned).