Key takeaways
- Squeezing a fingertip into a small plastic tube frequently ruptures red blood cells (haemolysis) and mixes tissue fluid into the sample.
- Capillary haemolysis and Royal Mail transit delays commonly void potassium, AST, LDH, folate, iron and hormone results.
- Many specialist tests, including coagulation screens, ESR, Quantiferon-TB Gold, homocysteine and multi-marker profiles, require a full venous sample.
- At Blood London (117a Harley Street), experienced phlebotomists draw venous blood into standard vacutainers with same-day courier transfer to The Doctors Laboratory (TDL). Book online or walk in 7 days a week.
Why finger-prick samples fail in the laboratory
Home finger-prick kits collect capillary blood from a lancet prick on the finger rather than venous blood from a vein in the arm. To fill a 0.5 ml microtainer tube, most people have to milk or squeeze the finger repeatedly. That mechanical pressure breaks fragile red blood cells open, a process called haemolysis, and forces interstitial tissue fluid into the tube.
When red cells rupture, intracellular substances spill into the serum. Potassium, aspartate transaminase (AST), lactate dehydrogenase (LDH), folate and serum iron can read falsely high, or the laboratory analyser rejects the haemolysed specimen altogether. If the sample also spends 24 to 72 hours uncentrifuged in a postbox, glucose falls and cell membranes degrade further.
Venous clinic collection vs postal capillary kits
| Feature | Venous Draw at Blood London | Postal Finger-Prick Kit |
|---|---|---|
| Sample type | Full venous blood in vacuum tubes | Capillary drops squeezed from fingertip |
| Haemolysis and clotting risk | Very low (closed vacuum draw) | High (squeezing and postal transit) |
| Transit to UKAS laboratory | Same-day courier to TDL London | 24 to 72 hours in Royal Mail post |
| Multi-tube and clotting panels | Full catalogue (1,000+ tests) | Limited to small capillary volumes |
| Accepted by IVF clinics and consultants | Yes (official clinic-collected TDL report) | Often rejected without identity check |
Which blood tests cannot be done by finger-prick?
Any test that requires sodium citrate coagulation tubes, whole-blood EDTA cellular analysis, rapid centrifugation or multiple tube types needs a venous blood draw. That includes Lupus Anticoagulant, D-dimer, Thrombophilia Screen, ESR, TB QuantiFERON-TB Gold, Plasma Homocysteine, ALEX3 Allergy Test and comprehensive Full Body Blood Tests.
One £50 blood-draw fee covers your entire basket
At Blood London, individual tests start from £14 and a single £50 phlebotomy fee covers every blood test in the same visit. Whether you book a single Iron Status Profile (£126.25) or combine Full Thyroid Profile (£163.13) and Liver Function Tests (£72.50), you only pay one £50 draw fee. Book your venous blood draw online or walk into Suite E, 117a Harley Street seven days a week.
Frequently asked questions
Can I walk in if my home finger-prick kit failed?
Yes. Many patients visit us after a postal kit clotted, haemolysed or could not collect enough blood. You can walk in without an appointment or book a 15-minute slot online.
How quickly do venous blood test results come back?
Because samples travel directly from Harley Street to The Doctors Laboratory by courier throughout the day, routine biochemistry, full blood count, ferritin, thyroid and liver profiles typically return within 24 hours.
Are clinic blood test reports accepted by NHS consultants and IVF clinics?
Yes. Every report is an original UKAS-accredited laboratory document from The Doctors Laboratory showing clinic venepuncture at 117a Harley Street.