Free blood test result interpreter: what your numbers mean

How it works

Most people in the UK get their blood results as a list of numbers with a reference range beside each one and no explanation of what any of it means. This page reads your number against the published UK guideline threshold for that marker and tells you which band it falls in and what the evidence says about that band. Three interpreters are live today. Vitamin D reads your 25-OH-D level. The iron panel reads ferritin, transferrin saturation, CRP, haemoglobin and MCV together. The B12 and folate interpreter reads total B12, active B12, folate, homocysteine and MCV.

Three things are worth stating before you use them. Nothing you enter leaves your device, nothing is saved, and no artificial intelligence is involved at any point. The interpretation comes from published thresholds and pre-written, referenced text, so the same number always returns the same reading and every source is shown underneath. You can paste your results straight from the NHS App or a test report and each interpreter will pick out its own lines for you to confirm before anything is read.

Safety profile

This page will not diagnose anything, and it will not tell you to take a specific amount of anything. Where a result sits in territory that UK guidance places with your GP, such as vitamin D deficiency correction, a substantially raised ferritin, or a B12 result in the deficiency band, the interpreter says so and stops there rather than filling the space with a supplement suggestion. Markers outside nutritional interpretation, including liver and kidney panels, hormones and the rest of the full blood count, are not interpreted, because interpreting them responsibly is a conversation with your GP and not something a page can do honestly.

Guideline positions

The thresholds behind every reading are published and stable. Vitamin D follows the UK classification of deficient below 25 nmol/L, insufficient from 25 to 50, and sufficient above 50, with a recognised caution in the clinical literature above 125 nmol/L and the NHS adult supplement limit of 100 micrograms (4,000 IU) daily. Ferritin follows the NICE iron deficiency guideline threshold of 30 micrograms per litre for adult iron deficiency, with WHO guidance on very low stores below 15 and on levels above 500 in adults who are unwell. A transferrin saturation below 20 percent alongside a ferritin of 30 or more is read as consistent with iron deficiency, and a raised CRP is read as making the ferritin unreliable. Total B12 follows the NICE guideline on vitamin B12 deficiency in over 16s, with deficiency below 180 ng/L and an indeterminate band from 180 to 350, an active B12 below 25 pmol/L read as consistent with deficiency, and folate cut-offs of 7 nmol/L for deficiency and 13 for low status.

Practical framework

One number is rarely the whole answer. Ferritin rises as part of an inflammatory response, because it behaves as a positive acute-phase reactant, so a ferritin sitting comfortably in range alongside a raised CRP can still be covering genuinely low iron stores, which is why laboratory guidance recommends looking at full iron studies rather than ferritin alone in that situation. Similarly, a transferrin saturation below 20 percent alongside a ferritin of 30 or more is consistent with iron deficiency even though the ferritin looks acceptable. Where B12 and folate are both low, guidance is to address the B12 alongside the folate rather than correcting folate on its own, because folate alone can improve the blood picture while neurological problems continue underneath. The interpreters apply these published rules when you enter more than one number, and say which pattern they are seeing.

Each interpreter reads one set of numbers once. What this page cannot do is hold your history, compare today against your last test, take account of what you are already taking, check for interactions and contraindications, or weigh any of it against how you are actually feeling week to week. Nutri365 does that continuously, which is a different job from the one this page performs, and the honest limit of a free single reading is worth knowing before you rely on it.

If what you actually want is your results interpreted together, over time, alongside your Oura data and how you feel, that is the Nutri Tailor app: search Nutri Tailor on the App Store or Google Play, or start on the web at nutritailor.co.uk/pages/nutri365, with a free trial to interpret your own results from day one.

Common misconceptions

A reference range describes how results are distributed across a population that was tested. A clinical threshold describes the level at which guidance says something should be acted on. They are not the same thing, and the gap between them is where most confusion sits.

Ferritin is the clearest example in UK practice. The NICE guideline on iron deficiency, updated in August 2024, sets adult iron deficiency at a ferritin below 30 micrograms per litre. Many laboratory reports still only flag results below 15, a threshold that comes from older WHO reference data. A ferritin of 22 can therefore be printed on your report as normal, with no flag beside it, while current UK guidance would class that same number as iron deficiency. This is not a rare edge case. It is one of the most common reasons people are told their bloods are fine while still feeling exhausted.

B12 carries the same gap. NICE classes a total B12 between 180 and 350 ng/L as an indeterminate result warranting a confirmatory test where there are symptoms, yet many reports print a result in this band without a flag because the laboratory reference range starts lower.