Blood sampling is a commonly well-known skill across a
lot of health care settings, used for a variety of reasons. In a health care
setting it is capable of providing a vast amount of information on an individual’s
general health, the presence of bacterial or viral infection, how well certain
organs are functioning and screening for specific genetic conditions (NHS
Choices, 2014). Outside of a health setting, blood sampling can be used to
profile individuals, examine efficacy of research interventions and give
information on changes during exercise (McLoughlin et al., 1992).
There are three main blood collection techniques:
Aterial, Venous and Capillary. Aterial blood samples are collected from an
artery and is primarily used to determine aterial blood gas and cardiac output
(WHO, 2010). This procedure is extremely invasive and rarely used outside an
intensive care setting. Venous blood samples are collected from a vein usually
at the antecubital area (bend of the elbow) (WHO, 2010). Venous samples are the
most frequently taken blood sample within the medical community and are used to
test for the widest range of conditions (Vajpayee, Graham & Bem, 2011).
Capillary blood samples involves puncturing epidermis and dermis layers of the
skin to access capillaries near the surface of the skin (WHO, 2010). Capillary
samples are taken from the ear lobe, finger or heel and can be used for
specific tests that only require a small amount of blood.
Capillary blood samples can be used to test:
The advantage of the capillary blood sampling
technique are that samples do not need to be sent away for testing and results
can be available almost immediately. The procedure is less invasive that
alternative blood sampling techniques and result in less soreness for the
participant. The disadvantages of the technique include increased risk of cross
infection of blood borne diseases and increased risk of small blood spillages.
The heel is normally only used as a sampling site for
paediatric and neonatal patients. In a clinical setting the finger is the most
common site with the ear lobe normally only used in mass screening or research
studies (WHO, 2010).
However the ear lobe may be a better site to use than
the finger because the skin is thinner, the site tends to be cleaner, the site
clots slower allowing for multiple samples from the same site and subjects
experience less soreness (Feliu et al., 1999: Dassonville et al., 1998). During
exercise it may be preferable to use the ear lobe site to avoid contamination
of the equipment by the finger tip site. Results during exercise can also vary
depending on the sampling site, with the type and intensity of the exercise
affecting lactate levels. Dassonville et al. (1998) found that during exercise
performed upon a cycle ergometer or a treadmill, samples taken from the ear
capillary had no significant difference to venous sample while finger tip
samples were significantly higher. However when exercise was performed upon an
arm crank ergometer, ear lobe sample were significantly lower than venous and
finger tip samples. In contrast Feliu et al. (1999) found significantly higher
values at the finger tip compared to the ear lobe during cycling, running and
rowing as well as at rest.
In capillary blood sampling the blood freely flows
from the puncture site exposing the participant, investigator and the
environment to the cross infection of blood borne diseases. Even in a combat
zone, capillary blood sampling were the highest risk activity for occupational
exposure to blood and bodily fluids represents more than 70% of of all
exposures (Murray et al., 2009). The means of transmission may be by direct
contact with an infected sample via a sharps injury or splashing on to broken
skin or mucous membrane. To reduce the risk of the procedure should follow the
guidelines set out in the General Blood Sampling Safety Procedure document by
Northumbria University available on Blackboard.
General guidelines include:
should be washed before and following sampling and between each subject
and abrasions must be covered with a suitable dressing
and glasses should be worn throughout sampling
latex (or equivalent) gloves must be worn for each new subject or if they
• A new
needle or puncture device must be used for each puncture
waste with the possibility that it could puncture the biohazard waste bin must
be placed in the sharps bin. This includes capillary tubes, puncture devices
and triglyceride sample strips.
over waste should be placed in the biohazard waste bag.
The participant should be made aware of the procedure,
have read the participant information and signed the consent form before
starting the procedure. The examiner and participant should remove and rings
and the subject should remove any ear rings. In a non exercising procedure the
participant may prefer to sit down during the procedure. Next the the examiner
should wash hands and cover any open wound or abrasion with a plaster or bandage before putting on the
protective goggles, apron and gloves.
The designated sample site (finger tip or ear lobe)
should be swabbed with the 70% alcohol swaps before being deposed into the
biohazard bag and the site allowed to air dry. After selecting how deep the
device will puncture by twisting, the safety tip should be removed off the
device and placed into the sharps bin. The selected puncture site should be
grasped with the opposite hand allowing for firm pressure to be applied by the
puncture device. After discharging the puncture device it should be disposed
immediately into the sharps bin. The puncture site for the finger tip should be
taken on the side of the finger away from the harder skin of the pad while the
ear lobe site should be on the edge of the earlobe between the cartilage and
bottom of the ear.
The site should be gently squeezed to encourage
bleeding with the first drop of blood wiped away with a tissue. Whilst gently
massaging and releasing near the puncture site the sample should be collected
using the appropriate collection device. To aid the capillary action of the
device and to stop air bubbles forming the capillary tubes and triglyceride
collection device should be held horizontal or slightly off horizontal with the
far end of the collection device higher than the puncture site. After collecting
the sample (fill the full collection device for glucose, lactate, haemoglobin
and triglyceride testing. Fill three quarters for haematocrit testing) the
sample should be analysed in the appropriate machine.
Triglyceride Testing – For measuring the amount of
triglyceride (a lipid derived from glycerol and three fatty acids) within the
blood. As the blood is squeezed out the collection device onto the test strip,
care should be taken to cover the holes around the black line on the collection
device to stop blood coming out of them.
Haemoglobin Testing: For measuring the amount of
haemoglobin (protein with the red blood cells). The collection disc must be
filled in one go so a large droplet of blood needs to squeezed from the
puncture wound before offering up the corner of the disc to the droplet.
Lactate and Glucose: For measurement of lactate and
glucose within the blood. After the sample is collected in the capillary tube,
the tube is placed into biosen consumable and shaken gently before being placed
into the biosen.
21 year old male, stature – 181cm, body mass – 81.5kg
All results were taken at rest.
Values Norm range
mmol/L 0.5-2.2 mmol/L
mmol/L 3.9-6.2 mmol/L*
g/dL Males: 13.8-17.2 g/dL
Females: 12.1-15.1 g/dL