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153
can be used as an alternative to arterial puncture
for arterial blood gas (ABG) determination in
infants.
FLASH FORWARD
Specialconsiderationsforcollectionfrompediatricandgeriatric
patientsarediscussedinChapter12.
However, some tests cannot be performed on
blood from a capillary collection. These include
blood cultures and most routine coagulation tests.
Capillary collection may not be appropriate for
severely dehydrated patients, because test results
may not be accurate. (This may also be a concern
with venipuncture for such patients.) Capillary
collection should not be used at sites that are swollen or where circulation or lymphatic drainage is
compromised (such as a limb on the same side as
a mastectomy).
DIFFERENCES BETWEEN VENOUS
AND CAPILLARY BLOOD
A capillary puncture collects blood from capillar-
ies. Because capillaries are the bridges between
arteries and veins, blood collected by capillary
puncture is a mixture of venous blood and arterial
blood. The arterial proportion in the sample is
increased when the collection site is warmed, as
may be done to help increase blood ow before
collection. Small amounts of tissue uid from the
puncture site may also be in the sample, especially
in the rst drop.
The levels of many substances are the same in
both capillary and venous blood, but this is not the
case for all substances, as indicated in Table 10-1.
For instance, the normal potassium reading obtained by capillary collection is lower than that in a
plasma sample obtained by venipuncture, but
higher than that in a serum sample obtained by
venipuncture. Because of these differences, results
obtained by the two techniques cannot be compared. For this reason as well, it is important to
record that the sample was obtained by capillary
collection.
TABLE 10-1 Reference Values in Capillary
and Venous Blood
Higher in Capillary Blood Higher in Venous Blood
•Glucose •Calcium
•Hemoglobin
•Potassium(serumsample) •Potassium(plasmasample)
•Totalprotein
EQUIPMENT FOR CAPILLARY
COLLECTION
Capillary collection equipment allows the phlebotomist to puncture the skin safely and collect the
sample quickly and efciently, with a minimum of
discomfort for the patient.
Skin Puncture Devices
Skin puncture devices in the modern health care
environment are designed with a retractable blade
per Occupational Safety and Health Administration
(OSHA) safety regulations. Some devices are contact
activated, whereas others require the phlebotomist
to depress a trigger to release the blade. Automatic
puncture devices (Figure 10-1) deliver a swift
puncture to a predetermined depth, which can be a
signicant advantage at sites where the bone is
close to the skin (see “Site Selection”). The dimensions of the puncture are controlled by the width and
A
CLINICAL TIP
Ifapatientneedsrepeateddeterminationsofpotassium,calcium,totalprotein,hemoglobin,orglucose,youmustusethe
samecollectiontechniqueeachtime.
Copyright 2016, 2011, 2007, 2002 by Saunders, an imprint of Elsevier Inc. All rights reserved.
B
FIGURE 10-1 A, BD Microtainer Contact-Activated Lancet.
B,TenderlettFinger IncisionDevice.(Acourtesyand©Becton,
Dickinson and Company. B usedwith permission fromInternationalTechnidyneCorporation[ITC]©2010.)
154
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CHAPTER 10 Capillary Collection http://evolve.elsevier.com/Warekois/phlebotomy
depth of the point. Some automatic puncture devices
have a platform that is positioned over the puncture
site and color coded for different depths. (The automatic devices designed for home glucose testing
make a cut that is too small for multiple tests or for
lling several microsample containers and are not
used in clinical practice.) Safety features include
retractable blades and locks that keep a blade from
being used a second time and prevent accidental
sticks to the phlebotomist.
The Lasette laser lancing device is unique in that
it uses a laser, rather than a sharp instrument, to
pierce the skin, which causes less pain and bruising
at the sample site. Cross-contamination between
patients is avoided by disposing of the single-use
lens cover between uses. The device is approved for
patients 5 years and older.
Microsample Containers
Microsample containers come in different sizes to
accommodate different volumes of blood.
Microcollection tubes (also called “bullets”)
hold up to 750 mL of blood. They are made of plastic and are available with a variety of anticoagu-
lants and additives (Figure 10-2). The tubes are
color coded by additive to match the coding of
evacuated containers. Microcollection tubes are
used for all types of dermal puncture collections
and are the most common type of collection containers used for dermal puncture samples. They are
also available with a plastic capillary tube that is
tted inside the container to aid in the collection of
the sample.
FLASH FORWARD
SeeAppendixAtoreviewmetricsymbols.
Capillary tubes come in either plastic or glass,
and in a range of sizes. These tubes are used primarily for the collection of samples for CBG determinations. Caraway or Natelson pipets are narrow
glass tubes with capacities up to about 470 mL.
The use of these tubes has declined in recent years
because of heightened attention to sharps injury
prevention, and OSHA recommends against using
glass tubes of this sort. Plastic capillary tubes are
increasingly being used instead.
Capillary tubes are available either plain, with a
blue band, or heparin coated, with a red, yellow, or
green band (colors may vary with the manufac-
turer). Once the sample is in the tube, one or both
ends are sealed. Sealing used to be done by pushing
the ends into soft clay. New, safer sealing methods
are recommended that instead t the ends with
small plastic caps. Both ends must be sealed for a
CBG determination. In the laboratory, the sample
may be centrifuged to separate cells from plasma or
serum. The sample can be removed with a syringe.
FLASH FORWARD
YouwilllearnaboutcollectingbloodgassamplesinChapter13.
Microhematocrit tubes are small tubes, either
plastic or glass, with a volume up to 75 mL. These
tubes are used infrequently and have been largely
replaced by microcollection containers. However
when a spun hematocrit is requested, a plastic
capillary tube can be used.
Finally, capillary collection is also used in
neonatal screening for a variety of inherited diseases. In this situation, no collection container is
used. Instead, drops of blood are applied directly to
specially prepared lter paper.
FIGURE 10-2 BDMicrotainer TubeswithBDMicrogardClosure.
(Courtesyand©Becton,DickinsonandCompany.)
FLASH FORWARD
YouwilllearnaboutneonatalscreeningcollectioninChapter21.
Additional Supplies
As in venipuncture, alcohol pads are used to prepare
the site, and gauze pads are used to help stop the
bleeding. A sharps disposal container is needed for
the lancet.
Warming devices increase circulation. Simple
towels or washcloths may be soaked in warm
water and applied to the site. Be sure that the site
is completely dry before puncture, however, as
residual water will cause hemolysis and dilution
of the specimen. Commercial warming packs are
Copyright 2016, 2011, 2007, 2002 by Saunders, an imprint of Elsevier Inc. All rights reserved.
http://evolve.elsevier.com/Warekois/phlebotomy CHAPTE R 10 Capillary Collection
https://t.me/med1917
also available. The pack is rst wrapped in a dry
towel and then activated by squeezing. Such “heel
warmers” are often used when blood must be col-
lected from infants. The temperature of the device
should not exceed 42° C, and it should be applied
for 3 to 5 minutes. Glass slides are used to prepare
blood smears for microscopic examination of
blood cells.
EPIDERMIS
155
Capillaries
FLASH FORWARD
YouwilllearnhowtoprepareabloodsmearinChapter14.
SITE SELECTION
General Considerations
Capillary collection should be performed on warm,
healthy skin that is free of scars, cuts, bruises, and
rashes. The site must be easily accessible and have
good capillary ow near the skin surface, but there
must be enough clearance above the underlying
bone to prevent the lancet from accidentally contacting it. Bone puncture can lead to osteochondri-
tis, a painful inammation of the bone or cartilage,
or osteomyelitis, a potentially serious, sometimes
fatal, bone infection.
You should also avoid skin that has been dam-
aged or compromised in any way. Specic areas to
avoid include skin that is callused, scarred, burned,
infected, bruised, edematous, or bluish. Also avoid
previous puncture sites as well as sites where circulation or lymphatic drainage is compromised.
Puncture Depth and Width
The depth of the puncture depends on the site and
the patient (Table 10-2). To minimize the risk of
inammation and infection, the lancet should
never penetrate more than 3.0 mm. For a heel
puncture, the maximum depth is 2.0 mm, because
the calcaneus, or heel bone, can lie very close to
the surface. For premature babies, the recommended depth is 0.65 to 0.85 mm.
TABLE 10-2 Puncture Depth
Use Depth
Fingerstick 3.0mm
Heelstick 2.0mm
Heelstick(prematureinfants
orneonates)
Bleedingtime 1.0mm
0.65–0.85mm
DERMIS
TISSUE
FIGURE 10-3 Theproper sitesforcapillarycollection are those
that provide an adequate capillary bed and sufcient clearance
from underlying bone. (From VanMeter KC, Hubert RJ: Gould’s
pathophysiology for the health professions,
Saunders,2015.)
ed. 5, St. Louis,
Puncture width should not exceed 2.4 mm
(Figure 10-3). At the right site, this achieves
adequate blood ow but remains well above the
bone. Puncture width is actually more important
than depth in determining blood ow, because
capillary beds may lie close to the skin, especially
for newborns. A wider cut severs more capillaries
and produces greater ow.
Capillary Collection Sites for Adults
and Older Children
For adults and for children older than 1 year, dermal
punctures are almost always performed on the
ngertips of the nondominant hand. The best sites are
the palmar surface of the distal segments of the
third (middle) and fourth (ring) ngers (Figure 10-4).
The thumb is likely to be callused, and the index
nger’s extra nerve endings make punctures more
painful. The little nger (pinky) has too little tissue
for safe puncture. If the ngers cannot be used,
the big toe may be an option—check the policy at
your workplace. Earlobes are never used for dermal
puncture.
FLASHBACK
AnatomicterminologywasdiscussedinChapter6.
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CHAPTER 10 Capillary Collection http://evolve.elsevier.com/Warekois/phlebotomy
A
FIGURE 10-4 Dermalpunctureinadultsandchildren isperformedonthethird(middle)orfourth(ring)nger,
onthepalmarsurfaceneartheeshycenterofthedistalsegment.
The puncture should be made near the eshy
center of the chosen nger. Avoid the edge of the
nger, as the underlying bone is too close to the sur-
face. As indicated in Figure 10-4, the puncture should
be made perpendicular to (across) the ridges of the
ngerprint, which lessens the ow of blood into the
grooves.
Capillary Collection Sites for Infants
For children younger than 1 year, there is too little
tissue available in any of the ngers. For this
reason, dermal puncture is performed in the heel
(Figure 10-5). As shown in Figure 10-6, only the
medial and lateral borders of the plantar (bottom)
surface can be used. The center of the plantar
surface is too close to the calcaneus, as is the posterior (back) surface. The arch is too close to nerves
and tendons. For older infants, the big toe may be
used if the heel is unacceptable. Be aware that
the heel may be callused on young children who
have begun to walk.
Yes
B
FIGURE 10-6 Dermal puncture in infants is performed on the
heel,onthemedialandlateralbordersonly.
C
No
AVOID THAT ERROR!
When phlebotomist Brandon Mayhew entered the waiting
roomand sawhisnextdraw,1-month-oldDerekStevens,he
knew he would need to be especially careful to make this
dermalcollectionassmoothaspossibleforboththeinfantand
thenervousmother.Hegreetedthemwarmly,smiledatDerek,
andquickly cleansedtheinfant’sbig toe,whichBrandonhad
chosenasthepuncturesite.Onceitwasdry,hecollectedthe
samplewithout delay, applied a bandage,labeledthe tubes,
andthankedthepatient.Twoweekslater,Derekwasadmitted
tothehospitalwithaboneinfection,andBrandonwasnamed
inalawsuit for injuring Derek.WhatdidBrandondowrong?
Whatshouldhehavedone?Andwhatshouldhedonow?
FIGURE 10-5 BD Microtainer Quikheel Lancet. (Courtesy and
©Becton,DickinsonandCo.)
CAPILLARY COLLECTION
Procedure 10-1 outlines the steps for a capillary
collection. In addition to these specic steps, you
should always greet the patient, identify the patient,
and obtain consent, as you would for a routine
venipuncture.
Copyright 2016, 2011, 2007, 2002 by Saunders, an imprint of Elsevier Inc. All rights reserved.
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PROCEDURE 10-1
Capillary Collection
1. After documenting on the requisition that
you are performing a capillary collection,
sanitize your hands and put on gloves.
Properhandsanitationandglovingtechniqueswerecoveredin
Procedures4-1and4-2.
2. Assemble your equipment.
Use the patient’s age and the tests ordered to
FLASHBACK
determine which type of collection tube you
will need, what type of skin puncture device
to use, and whether to use a warming device.
157
3. Select and clean the site.
Warm the area rst, if necessary. If the site
feels cold, it should be warmed for at least
3 minutes at a temperature no greater than
42° C. If a wet washcloth is used, be sure
to remove any residual water, as residual
water will cause hemolysis and dilution
of the specimen.
Use 70% isopropyl alcohol to clean the site.
Allow the site to dry completely. In addition
to causing stinging, contamination, and
hemolysis, residual alcohol interferes with
the formation of rounded drops of blood on
the skin surface. (Use of povidone–iodine
is not recommended for dermal punctures,
because it may elevate test results for
bilirubin, uric acid, phosphorus, and
potassium. Remember the acronym BURPP
to help you learn this group of tests.)
Massaging the nger proximal to the puncture
site (closer to the palm) can help increase
blood ow. To avoid hemolysis, massage
gently, and do not squeeze.
Continued
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CHAPTER 10 Capillary Collection http://evolve.elsevier.com/Warekois/phlebotomy
PROCEDURE 10-1—cont’d
Capillary Collection
4. Position and hold the area.
Hold the nger or heel rmly. This prevents
it from moving during the puncture and
reassures the patient.
Grasp the patient’s nger with its palmar
surface up, holding it between your thumb
and index nger.
To hold the patient’s heel, place your thumb in
the arch, wrap your hand over the top of the
foot, and place your index nger behind the
heel.
5. Make the puncture, and dispose of the blade
properly.
Align the device so the cut is made across the
ngerprint ridges or heel lines. This allows
the blood to ow out and make a rounded
drop, rather than run into the grooves.
Puncture the skin slightly lateral to the
center of the nger (that is, slightly toward
the pinky nger), so that the hand can be
tilted for easier blood ow into the container.
Do not lift the device immediately after the
puncture is complete. Count to two before
lifting the device to ensure that the blade
has made the puncture to the full depth and
then fully retracted. Scraping of the skin
may occur if the blade is not retracted.
Dispose of the used blade immediately in an
appropriate collection container.
Failure to obtain blood: If you are unable
to obtain sufcient blood with the rst
puncture, the policy at most institutions is
to attempt one more puncture. You must use
a sterile lancet to make the new puncture.
After two unsuccessful punctures, notify
the nursing station and contact a different
phlebotomist to complete the procedure.
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PROCEDURE 10-1—cont’d
Capillary Collection
6. Prepare to collect the sample.
Wipe away the rst drop of blood with a
clean gauze pad to prevent contaminating
the sample with tissue uid.
Keep the nger in a downward position to
help encourage blood ow.
You can alternate applying and releasing rm
pressure proximal to the site to increase
ow, but avoid constant massaging, as
this will cut off ow, cause hemolysis,
and introduce tissue uid back into
the sample.
159
7. Collect the sample.
Once blood is owing freely, position the
container for collection.
Microcollection tubes should be slanted
downward. Lightly touch the scoop of the
tube to the blood drop, and allow the blood
to run into the tube. Do not scrape the skin
with the container. This causes hemolysis,
activates platelets, and contaminates the
sample with epithelial skin cells.
Tap the container lightly to move blood to the
bottom. Close the lid after the sample has
been collected. Invert the tube 8 to 10 times
after lling if additives are present. Be careful
not to overll the microcollection tube con-
taining anticoagulant because the ratio of
anticoagulant to blood will be exceeded and
microclots will form. The collection will need
to be repeated due to inaccurate test results.
Order of collection: Platelet counts, complete blood
counts (CBCs) and other hematology tests are
collected rst, followed by chemistry tests.
Be mindful of specimens that require special
handling before transport.
Continued
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CHAPTER 10 Capillary Collection http://evolve.elsevier.com/Warekois/phlebotomy
PROCEDURE 10-1—cont’d
Capillary Collection
8. Complete the procedure.
Apply pressure to the puncture site using a
clean gauze square. Once bleeding has
stopped, you can bandage the site for older
children and adults. Do not use a bandage
on children younger than age 2, as they may
remove the bandage and choke on it. When
drawing blood from children and infants,
be especially careful that all equipment has
been picked up and bed rails have been
placed back in position.
Label the microsample container, and place it in
a larger holder for transport to the laboratory.
As always, thank the patient.
OTHER USES OF CAPILLARY
PUNCTURE
Capillary puncture is used for bleeding time
tests and ancillary blood glucose testing (also
called bedside glucose testing). It can also be used
as an alternative to arterial puncture for ABG
determination.
Bleeding Time Test
A bleeding time (BT) test measures the length of
time required for bleeding to stop after an incision is
made. In the past, this test was used before surgery to
help assess the overall integrity of primary hemostasis. Inconsistencies in the test have led to its replacement by the platelet function assay (PFA) or other
tests. These are performed not on dermal puncture
samples but on venous blood. The procedure is
included here because you may be called upon to
perform it nonetheless. To perform a BT test, an au-
tomated incision device is used, with the depth set at
1 mm, and length at 5 mm. Some devices make one
incision; others make two incisions at the same time.
The steps of the BT test are shown in Procedure 10-2.
FLASHBACK
HemostasiswasdiscussedinChapter7.
Results and Complications
Normal BT is 2 to 10 minutes and depends some-
what on the device used. Bleeding that does not stop
within 15 to 20 minutes means one of two things:
(1) either the patient has a condition that is interfer-
ing with normal platelet plug formation or (2) the
test was performed incorrectly—a capillary was
scratched, the incision was too deep, the lter paper
touched the incision site, or some technical error
was made. If only one incision was made, the test
may have to be repeated on the other arm. If two
incisions were made and the two BTs are within
several minutes of each other, it is unnecessary to
repeat the test. Be sure to learn the exact protocol
for your laboratory before this situation occurs.
Abnormally short BTs are probably caused by a test
error—for instance, the incision may have been too
shallow, the device may have been lifted too soon,
or there may have been hair at the incision site.
REVIEW FOR CERTIFICATION
Capillary collection is used for a variety of patients
with compromised or otherwise inaccessible veins,
including infants, or when only a small sample is
needed. A calibrated puncture device delivers a precise, carefully controlled puncture, avoiding contact
with the bone and reducing the risk of osteomyelitis
or osteochondritis. The size and purpose of the
sample dictate the collection container used,
although microcollection tubes are increasingly
used for most collections. The BT test assesses the
integrity of primary hemostasis by measuring the
time required to stop bleeding after a standard incision is made.
Copyright 2016, 2011, 2007, 2002 by Saunders, an imprint of Elsevier Inc. All rights reserved.
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PROCEDURE 10-2
Bleeding Time Test
1. Assemble your equipment.
You will need the following:
• Antiseptic materials (alcohol pads)
• Blood pressure cuff
• Automated BT device
• Stopwatch or timer with a second hand
• Filter paper
• Bandages
2. Prepare the patient.
Explain the procedure to the patient. Be sure to
explain that scarring may occur, especially in
dark-skinned patients.
Ask the patient about any medications he or
she is taking or has taken recently, especially
aspirin or other drugs that interfere with
clotting. Salicylates, including aspirin,
inhibit platelet function for 7 to 10 days
after the last dose. Ibuprofen inhibits
function for 24 hours. If the patient has
taken such medications recently, follow
the policy of your institution or consult
with your supervisor about proceeding
with the test.
3. Position the arm, select the site, and clean
the site.
Place the arm on a at, steady surface, with
the palm facing up. Select a site 5 cm below
the antecubital crease. The area must be
free of veins, scars, hair, and bruises. For
patients with very hairy arms, you may need
to shave the site before cleaning it. Clean
the site and allow it to dry, as you would
for other dermal procedures.
161
Continued
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CHAPTER 10 Capillary Collection http://evolve.elsevier.com/Warekois/phlebotomy
PROCEDURE 10-2—cont’d
Bleeding Time Test
4. Apply the blood pressure cuff.
Place the cuff on the upper arm. Inate it
to 40 mm Hg. This pressure must be
maintained throughout the procedure.
Wait 30 to 60 seconds to ensure that the
pressure is stable before making the
incision.
5. Position the device.
The blade is placed perpendicular to the
antecubital crease on the volar surface
of the forearm.
6. Make the incision, and start timing.
Press the device on the arm without making
an indentation.
Press the trigger.
Start timing as soon as the cut is made.
Remove the device only after the blade
has retracted.
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