Health Reference LibraryFerritin 18: is that low or normal?
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
By UK standards, yes, ferritin 18 µg/L is low. NICE-aligned practice reads anything below 30 as confirming iron deficiency, a threshold with 92 percent sensitivity and 98 percent specificity, and below 40 is 98 percent both. The WHO line of 15 is stricter, which is why 18 sometimes escapes a lab flag, but stores at 18 are thin enough to produce tiredness and under-par training long before anaemia. Reasonable response: iron-focused food plus a supplement, cause considered, ferritin retested at 8 to 12 weeks.
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 reads the iron reserve, and the 16 to 20 band is where the reserve is thin without being empty. Stores here still buffer haemoglobin, which is why blood counts usually look fine, but the margin is small: a heavy period cycle, a training block, a stomach bug that dents appetite, and the buffer is gone. This is also the band where lab reference ranges mislead most, because a range starting at 12 or 15 prints 18 as normal while the clinical evidence reads it as deficient.
Timing
From 18, sensible expectations are gentler than from single digits: energy changes tend to arrive inside the first month, and the store number moves meaningfully by the 8 to 12 week retest. Continue past feeling better, aiming for ferritin comfortably above 50, the level at which deficiency is excluded, and hold a maintenance pattern if the underlying drain, periods or training, continues.
Safety profile
The GP-first rule still applies to anyone with red flags: blood in stool or black stools, unexplained weight loss, persistent abdominal pain, or difficulty swallowing. A man or post-menopausal woman at 18 without an obvious dietary story should make cause-finding part of the plan rather than an afterthought. Iron supplementation is unsuitable in haemochromatosis, and iron products must stay away from children.
Special populations
For a menstruating woman, 18 is best read as early-stage depletion in progress, because monthly loss means the trajectory matters more than the snapshot; without a change, next year reads lower. For athletes, this is the classic performance band: research on iron and endurance repeatedly finds athletes in the teens and low twenties under-performing and responding to repletion, with foot-strike haemolysis and sweat loss adding drains a desk worker lacks. For men, 18 is unusual enough that diet alone rarely explains it, which moves the cause question forward. Post-menopause, the same logic as men applies. In pregnancy, below 30 is already the NHS action line, so 18 belongs in the midwife conversation now.
Guideline positions
The UK anchor is the NICE-aligned threshold: ferritin below 30 µg/L confirms iron deficiency, at 92 percent sensitivity and 98 percent specificity, with below 40 reaching 98 percent on both. The WHO 2020 guideline draws its healthy-adult line at 15, so 18 clears WHO by three points and misses the UK line by twelve. Where the two disagree, the UK threshold is the one your GP works to, and the one with the stronger diagnostic-accuracy data behind it.
Practical framework
This band rewards acting early, before the slide into the low teens. Food first and genuinely: red meat or legumes daily, vitamin C alongside plant iron, tea and coffee away from iron meals. A supplement makes the arithmetic work, and [Iron & Vitamin C](/products/iron-vitamin-c) pairs the two absorption partners, alternate days per NHS guidance. The cause deserves a thought even where no GP visit feels needed: periods, training load, diet pattern, and any gut symptoms. Retest at 8 to 12 weeks aiming to see the number climb toward and past 30; the [repletion timeline](/apps/learn/iron-supplementation-timeline-symptom-resolution-ferritin-normalisation) shows the realistic pace.
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).