Medichecks and Private Blood Test Results Explained
What a private finger-prick report actually tells you, why the numbers can look different from your GP's results, and how to keep every test in one place.
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· · Reviewed against the sources listed at the end of this page.
The Quick Answer
A private finger-prick test, of the kind sold by UK home-testing companies such as Medichecks, works the same way as an NHS blood test for most markers: a sample goes to an accredited laboratory, and a doctor adds a short comment before the report is sent back to you. The main practical differences are the collection method (a finger prick instead of a needle in the arm) and the fact that the reviewing doctor usually cannot follow you up directly.
Because a finger-prick sample is collected under pressure rather than drawn cleanly from a vein, a small number of markers, mainly potassium, LDH and AST, can read higher than your true level if red blood cells rupture during collection. Everything else on the panel is generally as reliable as a standard venous blood test.
How a Finger-Prick Sample Differs From an NHS Blood Draw
An NHS or GP blood test almost always uses venous blood, drawn from a vein in the arm by a trained phlebotomist with a needle and vacuum tube. A home test kit instead uses capillary blood, collected by pricking a fingertip with a small lancet and squeezing drops into a tiny collection tube.
Capillary blood is chemically very similar to venous blood, and for the majority of markers, cholesterol, thyroid hormones, vitamins, HbA1c and most others, the results are considered reliable. The difference that matters is the collection process itself. Filling a small tube from a finger prick often needs firm, repeated squeezing, and that pressure can rupture some red blood cells on the way, a process called haemolysis. A venous draw, taken more gently and in a larger volume, causes far less of this.
Reputable labs check every sample for visible haemolysis (a pink or red tinge to the fluid) and will flag or reject a result if it looks affected. Even so, mild haemolysis can sometimes pass unnoticed, which is why it is worth knowing which markers it tends to affect before reacting to a single unexpected number.
Markers Most Affected by a Finger-Prick Collection
These are the results most likely to be pushed upward by haemolysis during collection, rather than by a genuine change in your body. If one of these is your only abnormal result and you feel well, it is a reasonable thing to raise with your GP before assuming it reflects a real problem.
Potassium
Potassium sits mostly inside red blood cells rather than in the fluid around them. If cells rupture during a hard squeeze (haemolysis), that stored potassium spills into the sample and inflates the result, even when your true blood potassium is normal.
LDH (lactate dehydrogenase)
LDH is concentrated inside red blood cells. Haemolysis releases it into the sample by the same mechanism as potassium, independent of any real muscle, liver or heart signal.
AST (aspartate aminotransferase)
AST is present in red blood cells as well as the liver and muscle. A haemolysed sample can show a raised AST that has nothing to do with liver health.
Phosphate
Ruptured red cells and platelets release phosphate along with potassium and LDH, so the three often rise together on a haemolysed sample.
Magnesium
A smaller amount of magnesium is also held inside red blood cells and follows the same pattern, though the effect is usually less pronounced than for potassium.
Total protein and albumin
If a lot of tissue fluid is squeezed out during collection, the remaining sample becomes slightly more concentrated, which can nudge these two upward without reflecting a real change.
Why Your Result Might Look Different From the NHS
Two accredited laboratories testing an identical sample can report slightly different reference ranges, because each lab calibrates its own analyser against its own population of healthy people. A cholesterol reading of 5.3 mmol/L might sit inside one lab's range and just outside another's. Neither range is wrong; they are simply drawn from different reference populations and equipment.
Some private health check companies add a second, narrower band on top of the standard clinical range, often labelled something like “optimal”. Sitting outside that narrower band but inside the standard laboratory range is a very different situation from sitting outside the standard range itself, and it is worth checking which one a report is actually flagging against before you worry about a result.
Units can differ too. A UK private report will almost always use the same SI units as the NHS (mmol/L, IU/L, pmol/L and so on), but if you have ever tested overseas, for example while travelling or through an international company, watch for US-style units such as mg/dL for glucose or cholesterol, which need converting before you compare them directly against a UK result.
What Each Marker on a Typical Private Panel Means
UK home health check kits vary in what they include, but most build on this core set of markers. Panel names and exact contents differ between companies and tiers.
Full blood count (FBC)
Red cells, white cells and platelets. Screens for anaemia, infection and some clotting problems. Nearly every private health check panel includes this.
Lipid profile
Total cholesterol, LDL, HDL and triglycerides. Used alongside age, blood pressure and family history to estimate cardiovascular risk, not read as a single number in isolation.
Liver function tests
ALT, AST, GGT, bilirubin and ALP. A pattern across several of these tells your GP more than any one value on its own, which is one reason a single raised AST from a finger-prick sample is not usually acted on alone.
Kidney function
Creatinine and eGFR, sometimes with urea. Shows how well the kidneys are filtering waste from the blood.
Thyroid function (TSH)
Most basic private panels test TSH alone. TSH is a good first screen, but a small number of genuine thyroid problems only show up when free T4 and free T3 are also measured, so a normal TSH does not rule everything out if symptoms persist.
HbA1c
An average of your blood glucose over roughly the previous eight to twelve weeks. Used to screen for prediabetes and diabetes rather than a single blood sugar reading.
Vitamin D
Bone health and immune function. Low vitamin D is common in the UK, especially over autumn and winter when sunlight exposure drops.
Ferritin and iron studies
Ferritin reflects your iron stores. Low ferritin is one of the most common findings behind ongoing tiredness, particularly in menstruating women.
Vitamin B12 and folate
Needed for nerve function and healthy red blood cell production. Deficiency can cause tiredness, tingling and, if severe and prolonged, nerve damage.
CRP (C-reactive protein)
A general marker of inflammation or infection somewhere in the body. It is deliberately nonspecific and does not point to a particular cause on its own.
Testosterone and hormone panels
Often added to men’s and women’s wellness kits. Needs interpreting alongside symptoms, age and, for testosterone, the time of day the sample was taken, since levels vary through the day.
Understanding the Doctor's Comment and Colour Flags
Many UK private reports use a simple traffic-light style system alongside a short written comment. Wording varies between companies, but the underlying meaning is usually similar to this:
Green or "within range"
The value sits inside the laboratory’s reference interval for your age and sex. No action is usually suggested, though "within range" does not always mean optimal, and a result near the edge of the range can still be worth discussing if you have symptoms.
Amber or "borderline"
The value sits just outside the standard range, or inside a company’s own narrower optimal band. Often the advice is simply to monitor or repeat the test, rather than to act immediately.
Red, "abnormal" or "outside range"
The value is far enough from the reference interval that a doctor has flagged it for follow-up. This does not automatically mean something serious; it means the number needs a clinician to look at it alongside your history, not just the isolated figure.
"GP review recommended, please contact your GP surgery"
Private reviewing doctors typically cannot order further NHS tests, prescribe medication, or access your full medical record. This wording hands the next step to your own GP, who can see your history and decide whether repeat testing, referral or treatment is needed.
When to Contact Your GP Promptly, or Seek Urgent Care
Most private test results can wait for a routine GP appointment. A smaller number of findings, especially in combination with symptoms, should not wait:
A very high or very low potassium with symptoms
Potassium far outside range alongside palpitations, muscle weakness or dizziness should not wait for a routine appointment. Contact your GP surgery the same day, or call 111 or go to A&E if you feel unwell, since potassium at the extremes affects heart rhythm.
Chest pain, breathlessness or fainting, whatever the report says
Never wait on a blood test report if you have chest pain, sudden breathlessness, or you faint. These need immediate medical attention through 999 or A&E regardless of what any home test result shows.
Very low haemoglobin with breathlessness or a rapid heartbeat
Significant anaemia with symptoms warrants a same-day or next-day GP contact rather than a routine booking, particularly if you also notice black or bloody stools.
A markedly abnormal result with no obvious cause and no symptoms
If a single marker is well outside range but you feel completely well, it is reasonable to ask your GP about a repeat venous sample before assuming the worst, especially if that marker is one prone to finger-prick artefact such as potassium, LDH or AST.
Any result the reviewing doctor has flagged as urgent
If a private report explicitly says to seek urgent or same-day medical attention, follow that advice rather than waiting to discuss it at a routine appointment.
Five Steps After You Get a Private Result
A private test is most useful when it becomes one data point in an ongoing record rather than a single snapshot that gets filed away and forgotten.
Read the doctor’s written comment before the numbers
Most private reports include a short comment from a reviewing doctor above the results table. It usually tells you in plain terms whether anything needs following up, which is a faster and more reliable summary than scanning for red numbers yourself.
Check which range the report is using
Look for whether the report shows a single reference range or two ranges (a standard range and a narrower "optimal" range). Being outside the optimal range but inside the standard range is a very different situation from being outside both.
Treat one-off extreme results with caution
If potassium, LDH or AST is the only abnormal marker and you have no relevant symptoms, consider whether haemolysis during collection could explain it, and ask your GP whether a repeat test is worthwhile.
Book a GP appointment for anything flagged for follow-up
Bring the full report, not just the abnormal line, so your GP has the context of every other marker and your reference ranges. Mention that it was a private finger-prick sample.
Keep the report, don’t let it become a one-off snapshot
A single private test tells you how things looked on one day. The real value comes from comparing it against your next test, and against any NHS blood tests you have had, so trends over time can be told apart from the natural day-to-day wobble in a healthy result.
Sources and reference ranges
Adult reference ranges on this page follow the AACB and RCPA harmonised reference intervals unless stated otherwise; the range printed on your own report always takes precedence because laboratories differ.
Private Blood Test Results, Frequently Asked Questions
Is a private finger-prick blood test as accurate as an NHS blood test?
For most markers, a well-collected finger-prick sample gives a reliable result. But finger-prick samples are more prone to haemolysis (red blood cells rupturing during collection) than a venous draw taken by a phlebotomist, which can push certain markers, particularly potassium, LDH and AST, artificially high. If one of those three is the only abnormal result on an otherwise normal panel, it is worth asking about a repeat venous sample before assuming there is a real problem.
Why does my Medichecks or private test result look different from my NHS test?
Different laboratories can use different analysers, different reference ranges, and different units, so the same blood can produce slightly different numbers depending on which lab processed it. Some private companies also publish a narrower "optimal" range alongside the standard laboratory range, which is not the same thing as the range your NHS GP will use to decide whether to act. Always check which range a report is quoting against.
What does it mean when a private test report says a doctor has reviewed my results?
Most UK private testing companies have a doctor check each report and add a short written comment, sometimes alongside a colour flag such as green, amber or red. This is a one-off review of the numbers on the page. It is not the same as an ongoing GP relationship, and the reviewing doctor usually cannot order further tests, prescribe treatment or see your NHS medical history. A comment recommending GP follow-up means the next step happens through your own GP surgery.
Can I take my private blood test results to my NHS GP?
Yes. GPs regularly see private test results and will usually take them into account, especially if a marker is significantly out of range or you have symptoms. It helps to bring the full report rather than a screenshot of one number, and to mention it was a finger-prick sample if any result looks unexpectedly extreme, since your GP may want to repeat it with a venous sample before acting on it.
Why might my potassium or liver enzymes look abnormally high on a finger-prick test?
Squeezing a finger hard to collect enough blood can rupture red blood cells, a process called haemolysis. Potassium, LDH and AST are all present in high concentrations inside red blood cells, so haemolysis releases them into the sample and can push the reported level above range even though your actual blood level is normal. A visibly pink or red-tinged sample tube is a sign this may have happened, and some labs flag or reject samples that look haemolysed.
Are private blood test reference ranges the same as NHS ranges?
Not always. Reference ranges depend on the analyser and population the laboratory uses to set them, so two accredited labs can report slightly different normal ranges for the same marker. Some private health check companies also display an additional "optimal" band that is narrower than the standard clinical range. Neither is more medically correct than the other; they simply reflect different laboratories and different purposes.
How often can I retest with a private finger-prick kit?
There is no fixed rule, and it depends on what you are tracking. Markers that change slowly, such as cholesterol or HbA1c, are usually only worth repeating after a few months unless a doctor has asked for sooner. Markers being actively monitored, such as thyroid function after starting treatment, are typically retested on whatever schedule your doctor sets. Repeating a test purely because one result looked odd, especially potassium, LDH or AST, is reasonable and often clarifies whether it was a genuine finding or a collection artefact.
Is SmarterBlood affiliated with Medichecks or other private testing companies?
No. SmarterBlood is an independent tool. It is not affiliated with, endorsed by, or connected to any private testing company, and it does not sell or process blood tests itself. It simply reads the PDF or photo of a report you already have, from a private company, an NHS portal, or anywhere else, and lays every marker out in plain English alongside your other results.
Related Reading
Keep Your Private and NHS Results in One Place
SmarterBlood is free to use and is not affiliated with any testing company. Upload the PDF or a photo of your Medichecks report, or email it to mail@smarterblood.org, and its AI will pull out every marker, flag anything outside range, and plot it on the same timeline as your NHS or GP results, even when the two came from completely different labs.
This page provides general educational information about private finger-prick blood tests. It is not a substitute for professional medical advice, diagnosis or treatment, and it is not affiliated with Medichecks or any other testing company. Always consult your GP about abnormal blood test results, since they have access to your full medical history and can interpret your results in context. SmarterBlood does not provide medical care and does not sell or process blood tests.