Health Reference LibraryBlood test results explained, UK: what your numbers mean
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
Three rules unlock UK blood results. A reference range is where 95 percent of people fall rather than where health is best, so a result in range with symptoms still deserves a proper read, with ferritin the clearest case. Units need checking before biology, because vitamin D reports in nmol/L or ng/mL, B12 in ng/L or pmol/L, and folate in two systems. Markers read in pairs, with ferritin alongside CRP because inflammation inflates it, B12 alongside folate, and a surprising TSH repeated before acting. Each marker has its own family here, covering ferritin, vitamin D, B12, folate, haemoglobin, TSH, HbA1c, cholesterol and hs-CRP, with every band read against NICE and the next step stated.
Free blood test result interpreter
Paste your results once and every recognised value is picked out for you to check. Nothing you enter leaves this device. Nothing is saved. No AI is used, only published UK guideline thresholds.
How it works
Reference ranges are built by testing a local population and taking the middle 95 percent, which means they describe commonness rather than optimality, and they differ between labs, which is why the range printed on the report is the one that counts. Markers move for reasons beyond the obvious one. Ferritin is an inflammation-responsive protein as well as an iron store, so infection or inflammation raises it while stores stay low. TSH swings with illness, time of day and assay interference, biotin included. HbA1c reads three months of glucose rather than this morning's. Haemoglobin can look normal while iron stores are already empty, which is the low-ferritin-normal-haemoglobin pattern that explains so much unexplained tiredness. Pairs and trends beat single snapshots everywhere in this territory.
Timing
Results reach the NHS app within days. Re-test windows are marker-specific and stated on each family page: eight to twelve weeks for iron and vitamin D corrections, three months for HbA1c and lipids, six weeks minimum between TSH tests. Trends across two or three tests beat any single result.
Safety profile
Results flagged urgent by the lab or practice are acted on through the GP, not a webpage. Markedly abnormal single results get repeated before big conclusions, since sample and assay artefacts exist, biotin interference on thyroid and heart markers among them. Stopping a prescription because a number improved is a GP conversation. Nutri365 refers anything at clinical thresholds and checks for interactions and contraindications before suggesting any step.
Special populations
Pregnancy changes half these ranges, thyroid and haemoglobin especially, and pregnancy results are read with the midwife. Ranges for children are different territory and belong to the GP. Menstruating women read ferritin with extra care because the range floor sits below where symptoms resolve. People on thyroid hormone, statins or metformin have monitoring schedules that these pages complement rather than replace.
Guideline positions
Each family page anchors on the governing UK guideline: iron deficiency on the BSG guidance and NICE CKS thresholds on the [ferritin hub](/apps/learn/ferritin-blood-test-results-explained-uk-what-your-number-means); vitamin D on the UK 25/50 nmol/L cut-offs on the [vitamin D hub](/apps/learn/vitamin-d-blood-test-results-explained-uk-what-your-number-means); B12 and folate on NICE NG239 on the [B12 hub](/apps/learn/b12-blood-test-results-explained-uk-what-your-number-means) and [folate hub](/apps/learn/folate-blood-test-results-explained-uk-what-your-number-means); anaemia cut-offs on the [haemoglobin hub](/apps/learn/haemoglobin-blood-test-results-explained-uk-what-your-number-means); thyroid on NICE NG145 on the [TSH hub](/apps/learn/tsh-blood-test-results-explained-uk-what-your-number-means); diabetes thresholds on NICE NG28 on the [HbA1c bands](/apps/learn/what-do-hba1c-levels-mean-the-uk-bands-explained); lipids on NICE NG238 on the [cholesterol hub](/apps/learn/cholesterol-blood-test-results-explained-uk-what-your-number-means); and inflammation tiers on the CDC and AHA statement on the [hs-CRP hub](/apps/learn/hs-crp-blood-test-results-explained-uk-what-your-number-means).
Practical framework
The actual numbers come first, rather than a verbal all-fine, because the NHS app shows results in most practices and no action needed means no disease-level finding rather than optimal. The units and the lab's own range are noted for each marker. Each result then reads on its family page, where the specific band has its own entry: [ferritin](/apps/learn/ferritin-blood-test-results-explained-uk-what-your-number-means), [vitamin D](/apps/learn/vitamin-d-blood-test-results-explained-uk-what-your-number-means), [B12](/apps/learn/b12-blood-test-results-explained-uk-what-your-number-means), [folate](/apps/learn/folate-blood-test-results-explained-uk-what-your-number-means), [haemoglobin](/apps/learn/haemoglobin-blood-test-results-explained-uk-what-your-number-means), [TSH](/apps/learn/tsh-blood-test-results-explained-uk-what-your-number-means), [HbA1c](/apps/learn/what-do-hba1c-levels-mean-the-uk-bands-explained), [cholesterol](/apps/learn/cholesterol-blood-test-results-explained-uk-what-your-number-means), and [hs-CRP](/apps/learn/hs-crp-blood-test-results-explained-uk-what-your-number-means). The pairs read together, meaning ferritin with CRP, B12 with folate, and haemoglobin with ferritin. The page's next step is then acted on, whether supplement, retest window or GP conversation, one change at a time. Where tiredness started the search, the ordered work-through on [why am I always tired](/apps/learn/why-am-i-always-tired-the-honest-differential) sequences it. Nutri365 reads every marker together, against symptoms, tracking and history, checks for interactions and contraindications, and refers questions outside scope to a health specialist.
Common misconceptions
In range does not mean optimal. No action needed does not mean nothing worth understanding. A single TSH is not a diagnosis. Private panels with tighter optimal ranges are partly selling the retest. The trend across tests tells more than any single number.
Sources
- 2026. HRL results families (ferritin, vitamin D, B12, folate, haemoglobin, TSH, HbA1c, cholesterol, hs-CRP), each with NICE/BSG/CDC-AHA sources verified at build. Nutri Tailor HRL.
- 2025. NHS App. NHS.