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EspañolExplained, not just flagged
Each value comes with what it measures, how far it sits from your laboratory’s range, and what might be influencing it in your own situation.
With five questions to ask your GP
Checked against the ranges your own lab prints
NHS blood test results: what your numbers, flags and GP comments mean
A routine panel can run to dozens of lines, and almost always at least one value sits outside its range. Click “Read my results” to see which ones matter and why.
PDF or photo · NHS or private lab · Your report in a few minutes
TSH
To monitor · H4.90mU/L
Reference: 0.40 – 4.00 mU/L
- Your TSH is 0.90 above your laboratory’s upper limit: a slight rise, well below the level at which treatment is usually considered.
- TSH follows a daily rhythm: highest early in the morning, lower later in the day. A very early blood test can on its own put it just over the limit.
- A recent illness, even a mild one, can push TSH up while you recover: a rise of this size is often temporary.
- If free T4 is normal, this pattern is called subclinical hypothyroidism. It is common, particularly in women and with age, and some cases are back in range at the next test.
- With no symptoms reported, this single result is not a concern for now, but it is worth repeating in 6 to 8 weeks, in the morning, at the same laboratory.
Upload your NHS or private blood test results and get your full report
The full report sorts every marker by what needs attention, against the reference ranges printed by your own laboratory, then explains each one in plain English.
- Your name is removed: the engine reads your values and your context, not your identity.
- Your results are never used to train an AI, and never resold.
- You can delete a report, or your whole account, at any time. Where the data is hosted and read is set out in our privacy policy. Privacy policy
What the reading does, in three points
Every line, not only the flagged ones
All your results are gone through, line by line, and every marker is sorted, including the values your laboratory left unflagged.
Four levels of interpretation: requires medical follow-up, to monitor, normal, excellent
Your own laboratory’s ranges
The same figure does not mean the same thing from one laboratory to the next. The reading uses the ranges printed beside your results, not a generic table.
Your ranges, your age, your sex
One price
What the full report includes
- Every marker sorted into four levels: requires medical follow-up, to monitor, normal, excellent
- Every marker explained: its value, your laboratory’s range, what it measures
- A summary by system: iron, cholesterol, kidneys, liver, thyroid, immunity
- A prioritised action plan and advice tailored to your situation
- Five questions to ask your GP
- Your name removed before any analysis
Full report
$14.90
One-off payment, no subscription
- Refunded on request, no questions asked
- Your report in a few minutes
The full report is your blood test results explained one by one: which values deserve attention, why a value sits outside its range, what might be influencing it in your situation, and what to ask your GP. It helps you understand your results; it never makes a diagnosis, and the price is shown before you decide.
The method
Blood test results explained, one column at a time
A line of your results
| Test | Value | Unit | Reference range | Flag |
|---|---|---|---|---|
| Haemoglobin | 114 | g/L | 120 – 155 | L |
| Platelets | 262 | ×10⁹/L | 150 – 400 | — |
| TSH | 4.90 | mU/L | 0.40 – 4.00 | H |
The same test can be written two ways: MCV on one set of results, mean cell volume on another. Same measurement.
What each line of your results tells you
Layouts vary between laboratories, and the NHS App shows results differently from a printed sheet. But every line answers the same questions: which test, what value, in which unit, against which range, and whether it is flagged. Take them in that order and the list of numbers starts to make sense.
01 · Test
The test name tells you what was measured, and nothing more. Abbreviations vary between laboratories, so the same measurement can appear as MCV on one set of results and as mean cell volume on another, or as U&Es rather than urea and electrolytes. Start here: be clear what was measured before you worry about the number next to it.
02 · Value
Your value is one measurement, on one sample, on one morning. It is not an average of your health, and it shifts with how much you have drunk, the time of day, and what you did the evening before.
03 · Unit
The value means nothing without its unit. UK laboratories report haemoglobin in g/L, so 114 g/L is the same as 11.4 g/dL on an American report: the figure changes by a factor of ten, the result does not.
04 · Reference range
The reference range is the interval this laboratory considers usual, for its own method and, for some tests, for your age and sex. It is not a single national standard, and it is the only range that applies to your value.
05 · Flag
The way a result is flagged varies between laboratories and apps: an H or an L, an asterisk, a figure in bold, an arrow up or down, and sometimes nothing at all. In the NHS App you may also see a comment from your GP, such as ‘normal’, ‘satisfactory’ or ‘borderline’. Whatever its form, the flag is the same automatic comparison: your value against the two numbers beside it. What it never tells you is how far outside you are: a value just over the upper limit and a value at three times the limit get exactly the same mark.
Why an asterisk or a bold number does not mean you are ill
A laboratory range is not a line between ill and healthy. It is set to cover 95% of healthy people, which leaves the other 5% outside it while being perfectly well. In plain terms: out of twenty healthy people, one will have a flagged value on any given test, simply because of how the range was drawn.
2 in 3
A panel of twenty tests run on a healthy person has roughly a two-in-three chance of showing at least one flagged value.
Bold type, an asterisk, a highlighted cell: these show a distance from the group, not a verdict on you. What matters is which value, by how much, in which direction, alongside which others, and in what clinical situation.
A single flag on an otherwise unremarkable set of results is the most common result there is.
Why two laboratories do not print the same normal ranges
Reference ranges are not one national standard. Each laboratory sets or adopts its own, because they depend on the analyser, the reagent batch, the calibration, the measuring method and the population the laboratory serves. Two NHS hospital labs a few miles apart can print different upper limits for ferritin or TSH and both be right.
The practical consequence: never compare your value with a range you found elsewhere online. Compare it with the range printed beside it. And if your tests move to a different laboratory, expect a small jump in your results over time that comes from the method rather than from your health.
It is also why the full report takes the ranges from your own results instead of applying its own.
What a single marker never tells you
One line is a single data point. Your results are read as a whole, against your history, your medicines, and the reason the tests were requested in the first place.
A raised ALT after a stomach bug, after a night out, or after starting a new medicine is not the same finding three times over. A low haemoglobin with small red cells and low ferritin reads one way; the same haemoglobin with large red cells reads another. A value creeping up within its own range over three years can say more than one flagged result.
So the useful question is not “is this line normal?” but “what do these results say, and what do they leave open?” — which is where a test-by-test reading begins.
Want to know more?
Over twenty in-depth articles, grouped into four guides. Open the one that answers your question.
Common questions
The questions people in the UK ask most often about their blood test results, each answered with its source.
How can I interpret my blood test results?
Read each line in the same order: the test name, your value, its unit, the reference range printed beside it, then any flag. Only then look at how far a flagged value sits from its range, in which direction, and whether related lines move with it. A range describes healthy people tested with that laboratory’s method, so the one printed with your own results is the one that applies to you.
What does H or L mean on blood test results?
H means your value is above the laboratory’s reference range, L that it is below. Some laboratories use an asterisk, bold type or arrows instead, and some flag nothing at all. A flag tells you that you are outside the range, never by how much: a value just past the limit gets the same letter as one far beyond it, so compare the number with the two limits printed next to it.
What does ‘satisfactory’ mean on NHS blood test results?
It is a comment your GP adds after reviewing the result, not a laboratory flag. In the wording NHS surgeries use, ‘satisfactory’ means the doctor has looked at the result and, although it may be outside the normal range, it is not concerning: no further tests or treatment are needed. ‘Borderline’ means very close to the edge of the range and sometimes worth repeating; ‘abnormal but expected’ means outside the range because of a known condition or treatment.
Will my GP call me if my blood test results are bad?
If a result needs discussing, your GP, nurse or specialist should talk to you about it and explain what happens next. Some surgeries do not contact you at all when nothing needs doing. Results usually come back after a few days, sometimes a few weeks, and the NHS advises contacting your surgery if you have heard nothing after a few weeks. You may also be able to see them in the NHS App.
When to worry about blood test results?
Most flagged results are not a cause for alarm: flags are generated automatically, and a value slightly outside the range often needs no further action. An abnormal result can also be expected if you have a known condition, take certain medicines or have just been ill. It is worth acting when your surgery asks you to book an appointment or a repeat test, and if you are worried about a result and nobody has contacted you, get in touch with your GP surgery to ask what to do next.
What are red flags on a blood test?
Less the flag itself than the pattern around it: a value well beyond its range, several related lines out together (haemoglobin, red cell size and ferritin, for instance), a value drifting further at each test, or an abnormal result that matches symptoms you already have. Studies of patients reading their results online show that borderline values cause the most uncertainty, which is why a single result just over the limit is rarely a red flag on its own.
What can affect blood test results?
Many things besides illness. A recent meal, alcohol the day before, hard exercise, not drinking enough, some medicines and supplements, or the time of day can all move values. So can the sample itself: a tourniquet left on too long, or red cells damaged while the blood is taken (haemolysis), can for instance raise potassium. European laboratory medicine societies publish blood-sampling rules precisely to limit these effects.
How accurate are blood test results?
Very accurate on the whole, and errors mostly happen before the analysis itself. In a study of more than 51,000 hospital tests, about 3 in 1,000 were affected by an error, and 62% of those arose before the sample reached the analyser: labelling, taking the blood, transport. Errors in the analysis proper made up 15%. That is why a surprising, isolated result is usually repeated before anything is decided.
Do all cancers show up in blood tests?
No, and a normal set of results does not rule cancer out. Some changes, such as unexplained inflammation, make a serious illness more likely and lead to further tests: in a large UK study in general practice, 3.5% of patients with a raised inflammation marker were diagnosed with cancer within a year, against 1.5% when it was normal. Yet those same markers missed around half of cancers, so they can neither alarm nor reassure on their own.
Can stress affect blood test results?
A little, and only for a short time. A meta-analysis of more than 300 studies found that stress lasting just minutes already shifts some immune measures in the blood, while long-term stress dampens others. In practice, what comes with stress often matters more: a short night, a skipped meal, extra coffee, a hard workout the day before. If a value seems out of line with how you feel, mention it to your GP before drawing conclusions.
How much does the full report cost?
It is a single one-off payment, with no subscription, refunded on request with no questions asked. It sorts every marker against your own laboratory’s ranges, names the ones that deserve attention, explains each of them, and adds a summary by system, an action plan and five questions to ask your GP. The price is shown before you decide.