What your bloodwork can and cannot tell you
A blood panel tells you what was circulating in your bloodstream on the morning you gave the sample. That is genuinely useful. It is not a verdict on your health. Read alongside your symptoms, your history and your previous panels, bloodwork is one of the most informative things you can do for yourself. Read in isolation, marker by marker, against a range printed in the margin of the page, it will mislead you in both directions.
Almost every question we are asked about a specific marker turns out to be a version of this one: how much weight should I put on this number? Here is the honest answer, and the reasoning behind it.
Key takeaways
A reference range describes a population that a laboratory tested. It is not a target set for you.
One result is weak evidence. The same marker across three panels is strong evidence.
Markers are read in groups, because the systems that produce them work in groups.
Bloodwork describes what is happening. It rarely explains why on its own.
Anything acute, painful or alarming belongs with your GP first, not with an interpretation service.
What does a blood panel actually measure?
Nearly everything on a standard panel is a concentration: how much of a substance is dissolved in a given volume of blood at the moment the needle went in. That covers cells such as haemoglobin, white cells and platelets; transport and storage proteins such as ferritin, transferrin and albumin; electrolytes and minerals; hormones; enzymes that leak out of organs under strain; and metabolic markers such as fasting glucose and HbA1c.
Two things follow from that. First, a concentration is not the same as a total body store. Blood is the delivery network, not the warehouse. Second, most of what is measured is in transit — being made, carried, used or cleared — so the number you see is a rate of flow caught mid-movement, not a fixed quantity sitting still.
What can bloodwork tell you?
Quite a lot, when the question is well posed. A panel is good at answering:
Is a system under obvious strain right now? Liver enzymes, kidney function and inflammatory markers are sensitive to current load.
Are specific stores depleted? Iron, B12, folate and vitamin D are among the few things blood measures reasonably well as reserves.
How has glucose been handled recently? HbA1c averages roughly the last three months, which is why it is harder to game than a single fasting reading.
Is a hormonal axis compensating? A pituitary signal rising while the downstream hormone stays flat is a recognisable pattern, and it is the whole reason to read a full thyroid panel rather than TSH alone.
Which way are things moving? This one only works if you have more than one panel, which is why we keep results together rather than leaving them scattered across PDFs.
Is there a common, testable explanation for a symptom? Persistent tiredness is the classic example, and iron studies are usually the first place to look.
What can bloodwork not tell you?
The limits are just as important, and they are where most of the disappointment comes from.
Why a marker sits where it does. A raised inflammatory marker says there is inflammation somewhere. It does not say where, or from what.
How you feel. There is no marker for exhaustion, and plenty of people feel awful with an unremarkable panel.
What is happening inside tissues. Blood concentrations and tissue-level activity can diverge, which is a large part of why thyroid symptoms and thyroid numbers sometimes disagree.
What will happen. Markers shift probabilities. They do not predict individuals.
Whether an intervention is working — unless the marker you are watching actually tracks that intervention on a timescale short enough to see. That gap matters most when weighing up a claim about a supplement or compound.
Why is a normal result not the same as an optimal one?
A reference range is built from the people a laboratory happens to test. The lab takes that sample population, removes the obvious outliers, and reports the central band that roughly 95 per cent of them fall inside. That is a description of who walked through the door. It is not a statement about where a given person functions best.
Two consequences follow. A result inside the range is not automatically right for you: by construction, one in twenty healthy people sits outside it, and plenty of people sit inside it while feeling terrible. And a result slightly outside the range is not automatically a problem: ranges shift between laboratories, between assay methods and between age and sex groups, so the same sample can be flagged by one lab and not another.
Lens | What it tells you | Where it fails |
|---|---|---|
Reference range | Whether you sit inside the band a lab sees in its own population | Says nothing about you specifically, and moves between labs |
Optimal range | Where a marker sits in people who are well, rather than merely not diagnosed | Less standardised, and genuinely contested for some markers |
Your own trend | Whether a marker is moving, how fast, and in which direction | Needs at least two comparable panels before it exists at all |
Of the three, the trend is usually the most informative and the most neglected. A ferritin of 42 means one thing if it was 38 last year and something quite different if it was 110.
Why do the same person's results change between tests?
Because a great deal moves the number besides your underlying health. Time of day matters for cortisol, iron and testosterone. Fasting state changes glucose, triglycerides and insulin. Hydration concentrates or dilutes almost everything. Recent hard exercise raises muscle enzymes and inflammatory markers. A cold three days ago will still be visible in ferritin and hs-CRP. Cycle phase moves the sex hormones dramatically, which is the central difficulty in tracking hormones through perimenopause. High-dose biotin supplements interfere with some assays outright.
None of this makes testing unreliable. It makes conditions part of the result. Same laboratory, similar time of day, similar preparation, and a note of anything unusual in the week beforehand — that is what turns two panels into a comparison instead of two unrelated snapshots.
Why are markers read in groups?
Because reading them one at a time discards the information that matters most. Ferritin is the cleanest example: it stores iron, but it also rises during inflammation, so a ferritin that looks adequate next to a raised hs-CRP may be masking depleted stores entirely. Read alone, it passes. Read next to its neighbour, it does not.
Thyroid works the same way. A TSH drifting upward while free T3 sits low is a different finding from either number on its own — it suggests a system working harder to hold output steady. Each value passes in isolation. Together they say something specific.
Markers are read together, because that is how they move.
This is the reasoning behind the Traffic Light method we use in every DearLife 360: rather than checking each marker against a range on its own, results are weighed against each other and then sorted into three bands, so the pattern becomes the finding rather than a list of individually unremarkable numbers.
What should you do with a result you do not understand?
Check whether it is urgent. Markedly abnormal results, or any result alongside new or severe symptoms, go to your GP now. Interpretation is for understanding, not for triage.
Find the previous value. Direction beats position almost every time.
Write down the conditions. Time, fasting state, illness, training load, supplements, cycle day.
Look at its neighbours. Almost no marker is interpretable alone.
Turn it into one specific question you can put to a clinician — far more useful in a short appointment than a printout and a general worry.
Frequently asked questions
How often should I have bloodwork done?
For most people without a specific clinical reason, once a year is enough to build a trend, with a repeat at around three months if something is actively being followed or changed. Testing more often than a marker can meaningfully move mostly generates noise.
Is a result just outside the reference range a problem?
Not necessarily. Ranges are population bands with a built-in false-positive rate, and they differ between laboratories. A marginal result is a prompt to look at the trend and the surrounding markers, not a diagnosis in itself.
Should I fast before a blood test?
Follow whatever your requesting doctor or pathology collector specifies, since it depends on which markers are being run. What matters for comparison is consistency: if you fasted last time, fast this time, and note it either way.
Can a blood test tell me my biological age?
Biological age scores are calculated from ordinary markers using a chosen formula. They are a useful way to summarise several results in one figure, but the underlying markers are the real information, and different formulas give different ages from the same blood.
Do I still need my GP if I have my results interpreted?
Yes. An interpretation explains what your results show and what is worth asking about. It does not diagnose, prescribe or replace medical care. That distinction is deliberate, and you can read more about how and why we work that way.
Reading your own panel
If you already have results and want them read as a whole rather than a list, that is exactly what the DearLife 360 is for: every marker placed in context, banded, and written out in plain language, with clear next questions at the end. If you do not have recent bloodwork yet, we can arrange a comprehensive panel and read it from there.