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Getting a blood test result and reading a long list of acronyms, numbers and asterisks isn’t much use if nothing on the page explains what any of it means. This guide walks through how to read a UK private or NHS blood test result, what “high” and “low” mean, and, most importantly, when a result is worth acting on and when it isn’t.
This is a guide for patients, not a substitute for a clinical opinion. If you’re worried about your results, contact the clinician who ordered them or your GP.
A typical UK blood test result page shows, for each test:
Some private providers add:
A reference range is not a “healthy” or “unhealthy” line. It’s the range that around 95% of apparently healthy adults sit within. That means, statistically, one in every 20 healthy people has at least one result outside the range on any given day, purely by chance.
This is why single results that are just outside the range usually don’t matter. What matters is:
A ferritin of 14 when the lower reference is 15 is not the same problem as a ferritin of 4. A cholesterol of 5.2 when the upper reference is 5.0 is not the same problem as a cholesterol of 8.7.
Below is a plain-English summary of the most commonly reported markers on a UK blood test. Reference ranges vary by laboratory and by age and sex, so always use the range printed on your own report, not a general one. The NHS overview of blood tests and pathology is a useful further read.
Haemoglobin is the protein in red blood cells that carries oxygen. Low haemoglobin is anaemia, the most common causes in the UK are iron deficiency, B12/folate deficiency, and heavy periods.
Related test on Swift: Full Blood Count, Anaemia Blood Test.
White blood cells fight infection. A raised WBC often signals a recent or current infection or inflammation. A low WBC can result from viral infections, some medications, or a bone marrow issue.
Platelets help blood clot. Very low platelets can raise the risk of bleeding; very high platelets can raise clot risk. Both extremes warrant a GP conversation.
Ferritin is your body’s iron storage protein. Low ferritin is the earliest sign of iron deficiency and often precedes anaemia. High ferritin can be a marker of inflammation, liver issues, or (rarely) haemochromatosis.
Related test: Iron Status Blood Test, Advanced Iron Blood Test.
TSH is the pituitary signal that tells the thyroid gland to produce hormone. Free T4 and Free T3 are the thyroid hormones circulating in the blood.
Related test: Thyroid Function Panel.
The main store form of vitamin D. UK guidance (NICE and Public Health England) considers levels below 25 nmol/L a deficiency, 25–50 nmol/L insufficient, and 50 nmol/L or above sufficient. Levels are typically lower in autumn and winter.
Related test: Vitamin D Blood Test.
B12 and folate are both needed for red cell production and nervous system function. Low B12 is common in vegetarians, vegans, older adults, and people taking metformin or long-term proton pump inhibitors.
Related test: Vitamin D, B12 & Folate Levels.
Your lipid panel. Total cholesterol is total. LDL is the “carrying” cholesterol (higher = higher cardiovascular risk). HDL is the “clearing” cholesterol (higher = lower risk). Triglycerides are storage fats.
Related test: Cholesterol Blood Test, Heart Health Markers.
HbA1c reflects your average blood glucose over the previous 8–12 weeks. The UK diagnostic thresholds (per NICE) are:
Related test: Diabetes Health Checks.
These test the liver. Isolated mildly raised ALT or AST is common and often has non-serious causes (recent alcohol, a viral illness, muscle injury). A pattern of consistently raised results should be investigated.
Related test: Liver Function.
Creatinine and urea reflect how well the kidneys are filtering. eGFR (estimated glomerular filtration rate) is calculated from creatinine and gives a percentage-like measure of kidney function.
Related test: Kidney Function (U&E) Blood Test.
A general inflammation marker. Raised CRP means inflammation somewhere, but doesn’t tell you where. Recent infection, injury, autoimmune flare, or (occasionally) a chronic underlying condition are all possible.
A marker of prostate cell activity. Higher levels can indicate benign prostate enlargement, prostatitis, or (in some cases) prostate cancer. Interpretation requires age context, see the NHS PSA testing information.
Related test: Prostate Health Blood Test (PSA).
Nine out of ten “slightly out of range” results are one of:
The right move for a slightly abnormal result is usually:
Some results warrant contacting a doctor without waiting for a routine appointment:
A reputable private provider will flag these on the report and, in most cases, phone you. If you get a private report showing any of the above, contact the ordering provider immediately or go to A&E if you feel unwell.
“H” means the result is above the reference range for the general adult population. It doesn’t necessarily mean something is wrong, how far above matters, and so does the specific marker. Read the doctor’s commentary if there is one, or ask your GP.
“L” means the result is below the reference range. As with “H”, the significance depends on the marker and how far below the range you are.
Sometimes yes. Reference ranges are set so that 5% of healthy people sit outside them by chance. But a slight abnormality combined with a matching symptom, or a pattern over multiple tests, is worth discussing with a clinician.
Reference ranges are population-based and adequate for most decisions, but they don’t account for individual variation. A very active person will often have different ferritin, creatine kinase, and cortisol than the reference range assumes.
Analytical variation (the lab’s own margin of error), biological variation (natural day-to-day change in your body), timing, hydration, and food all contribute. A change of 5 to 10% between two tests taken a week apart is usually not meaningful.
UK private blood test providers who include doctor commentary use GMC-registered clinicians. The commentary is not a substitute for a full consultation but is a reasonable first read of what your results suggest.
Yes. Ask the practice to add the results to your medical record. Some practices are more receptive to this than others, a printed copy makes it easier.
Indefinitely. Trend data is the single most useful thing you can build over years of testing. Save the PDFs somewhere secure.
No. The provider sends results to you (and, if you asked, to a named GP). Your GP will only add them to your NHS record if you or they ask them to.
Swift Blood Tests offers home visits across Essex, Bromley and Surrey and clinic appointments in Billericay, with UKAS-accredited laboratory analysis and results in 24–48 hours. Browse the full range of tests or book a home visit. Not sure which test you need? Call 01277 652067.
