Explained · Sample collection
Both are real blood, both go to accredited laboratories, and both give useful results. The difference is not that one is accurate and the other is not. It is volume, handling and what that allows: a finger-prick yields a few hundred microlitres squeezed from a capillary bed, a venous draw yields several millilitres straight from a vein into vacuum tubes. That decides how many markers can be run from one sample, how often a sample fails, and which individual results you can trust to a decimal place. This page explains the difference honestly, including when a finger-prick is the better buy.
TrueVitals is venous only, at 103 UK clinics or at your home. No kits, nothing to post.
Last reviewed 17 September 2026
The short answer
For a small number of stable markers, a well-collected finger-prick sample is fine, and it is cheaper and more convenient. For a large panel, for hormones, for anything you want to compare like-for-like against a result six months from now, and for the markers that are distorted when red cells rupture during collection, a venous draw is the better sample. The practical rule: finger-prick for one or two things you already know you want, venous for the full picture.
Side by side
| Finger-prick (capillary) | Venous draw | |
|---|---|---|
| How it is collected | A lancet pierces the fingertip; you squeeze drops into a small tube, usually yourself, at home | A registered phlebotomist takes blood from a vein into vacuum tubes, at a clinic or your home |
| Usable volume | Roughly 0.3 to 0.6 ml if collection goes well | 10 to 30 ml, split across tubes with different preservatives |
| How many markers | Panels generally top out around 50 to 60; each added marker competes for the same few drops | 140 or 230 comfortably, because each assay gets the volume it needs |
| What the sample actually is | A mix of capillary and venous blood with some interstitial fluid, which is why several markers read slightly differently | Pure venous blood, which is what most laboratory reference ranges were established on |
| Haemolysis (ruptured red cells) | Common. Squeezing the finger forces cells through a small opening and breaks them, releasing what is inside | Uncommon with good technique and a proper needle gauge |
| Failed or insufficient samples | A recognised problem; providers send replacement kits, which costs you another week | Rare, and the phlebotomist can simply take more at the time |
| Repeatability over time | Variable: depends on how well you squeezed, how warm your hands were and how fast you filled the tube | High: the same method by a professional every time, so a change in the number means a change in you |
| Convenience | Excellent. Through the letterbox, done in ten minutes, no appointment | Good. A clinic visit, or a phlebotomist to your door for £39 |
| Cost | Lower, no collection fee | Adds £19 at a clinic or £39 at home |
| Best for | One or two known markers, cheaply, with no appointment | Comprehensive panels, hormones, and anything you intend to track |
The technical bit
When a red blood cell ruptures, everything inside it spills into the sample. That is haemolysis, and it is the single biggest reason finger-prick results differ from venous ones. It does not affect every marker equally; it affects the ones that are concentrated inside red cells or that the assay is sensitive to.
| Marker | What haemolysis does | Consequence |
|---|---|---|
| Potassium | Red cells are full of it; rupture releases it into the sample | Reads falsely high, sometimes alarmingly so. A common reason a result gets flagged and repeated |
| Liver enzymes (AST, LDH) | Also present inside red cells | Reads falsely raised, which can look like liver damage that is not there |
| Ferritin | Iron-related proteins released from cells | Can read higher than reality, which risks missing an iron deficiency |
| Hormones (testosterone, oestradiol, cortisol) | Assays are sensitive to sample quality and volume; many need more serum than a finger-prick reliably provides | Wider variability between repeat samples, which matters most when you are tracking a dose |
| Vitamin B12 and folate | Both are present in red cells | Can read higher than the true serum level |
| Glucose | Capillary glucose genuinely differs from venous, particularly after eating | Not an error, but not directly comparable with a venous fasting glucose |
| HbA1c, cholesterol, vitamin D, TSH, hs-CRP | Comparatively robust | These are the markers finger-prick handles well, which is why the good kits focus on them |
A good laboratory measures the haemolysis index and rejects or flags a sample that is too degraded, which is why kits sometimes come back with markers missing. That is the system working, not failing. Guides: ferritin, hormones, B12, our labs and standards.
Being fair about it
Buy the kit
A vitamin D level after winter. An HbA1c to keep an eye on. A cholesterol recheck your GP asked for. These are robust markers, the kits are cheap, and a clinic trip adds nothing.
Buy the kit
Remote location, no clinic nearby, no at-home coverage, or a schedule that makes an appointment impossible. A finger-prick result is far better than no result, and anyone who tells you otherwise is selling.
Buy the kit
If a venepuncture is the reason you would not test at all, take the finger-prick. The best test is the one you actually do. Most people find a professional draw easier than they expect, but that is your call to make.
Get the draw
Anything past about 50 markers needs the volume. This is the hard physical limit that no amount of technology gets around: several assays each need their own millilitre.
Get the draw
TRT, HRT, thyroid medication or anything where the next decision depends on the number. Repeatability is the whole point, and a professional draw gives it. TRT monitoring.On HRT.
Get the draw
One test is a number; two are a trend. A trend only means something if both samples were taken the same way. Mixing methods between tests makes the comparison unreliable.
How TrueVitals does it
Every TrueVitals sample is a venous draw taken by a registered phlebotomist, whether at one of 103 UK clinics for £19 or at your kitchen table for £39. There is no kit to collect, nothing to squeeze and nothing to post. That is what allows 140 or 230 markers from one appointment, reliable hormone results, and a report next year that can be compared honestly with this year's. The at-home visit is the part people do not expect: same phlebotomist, same tubes, same laboratory, same result, just in your own kitchen.
Advanced
74 biomarkers · £269
Already more markers than any finger-prick panel can carry, with full thyroid, ApoB, full iron studies and core hormones.
View AdvancedMost popular
Ultimate
140 biomarkers · £349
Adds Lp(a), fasting insulin and HOMA-IR, cystatin C, the complete hormone set with SHBG, PSA with free ratio and tumour markers.
View UltimateSignature
230 biomarkers · £799
Processed by Randox and collected at a Randox clinic with physical measurements. The deepest panel in the UK, and only possible with a venous sample.
View SignatureClinic £19, at home £39, included on Signature. Fast from 10pm and book a morning slot. How the home visit works.
Who uses what
| Provider | Default method | Venous available? |
|---|---|---|
| Thriva | Finger-prick kit by post | No |
| Medichecks | Finger-prick kit by post | Yes, at a partner clinic or nurse visit for a fee |
| Forth | Finger-prick kit by post | Yes, for an extra fee |
| Randox Health | Venous at its own clinics | Venous only |
| London Medical Laboratory | Venous at partner clinics | Venous, with some finger-prick options |
| TrueVitals | Venous at 103 clinics or at home | Venous only, at-home included |
Provider details change; check before booking. Full comparisons: Thriva vs Forth, Medichecks vs Randox, every UK provider.
FAQs
For robust markers such as HbA1c, cholesterol, vitamin D, TSH and hs-CRP, a well-collected finger-prick sample analysed at an accredited laboratory gives a reliable result. The problems arise with markers affected by haemolysis (potassium, AST, LDH, ferritin, B12) and with assays that need more serum than a few drops provide, particularly hormones.
Volume. Each assay consumes a set amount of serum, and a finger-prick yields a fraction of a millilitre. A venous draw yields ten to thirty millilitres across several tubes, which is why 140 or 230 markers from one appointment is possible.
It is the rupture of red blood cells during or after collection, releasing their contents into the sample. Squeezing a fingertip makes it far more likely. It falsely raises potassium, AST, LDH, ferritin and B12 among others, and a badly haemolysed sample is rejected by the laboratory, which is why kits sometimes return incomplete results.
Cautiously, and not for everything. Capillary and venous blood genuinely differ for some markers, and collection quality varies more with finger-prick. If you are tracking a change over time, use the same method each time, ideally a professional venous draw.
Most people find it easier than expected and less irritating than a lancet in the fingertip, which stays sore for a day. It takes under a minute, and a registered phlebotomist does it hundreds of times a week. If you are anxious about needles, say so when booking; it is a very common request.
Identical. The same registered phlebotomist takes the same sample into the same tubes, and it goes to the same UKAS-accredited laboratory on the same courier. The only difference is the chair you are sitting in.
If you want one or two robust markers cheaply and cannot easily get to a clinic, a finger-prick kit is a sensible buy. If you want a comprehensive picture, reliable hormones, or results you will compare against a future test, choose a venous draw.
140 biomarkers from a single venous sample, taken by a registered phlebotomist at a clinic or your kitchen table, with a written report within 4 working days.
Labs and standards · Thriva vs Forth · Medichecks vs Randox · How it works · Find a clinic
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