MICROCOLLECTION (CAPILLARY PUNCTURE)

MICROCOLLECTION

(CAPILLARY PUNCTURE)

What is Capillary Puncture?

A few drops of blood specimen can be obtained

by making an incision in the capillary bed in the

dermal layer

Also known as dermal or skin puncture

Collection sites include the finger tips (which

ones?) of adults or children over the age of two;

and heels for infants.

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Purpose of Capillary Puncture

• Adults & Older Children: • No accessible veins e.g. obese patients,

burns/scars, hematoma at the puncture site

• Patient has thrombotic tendencies

• Save veins for other procedures e.g. chemotherapy

• Intense fear of needles

• Point of care testing

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Purpose of Capillary Puncture

Children/infants: Preferred method

Removing large volumes of blood is not advisable

Anemia, cardiac arrest (if large volume removed rapidly)

Chances of tissue damage are higher in children during venipuncture

Some tests are designed only for dermal puncture e.g. newborn screens

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Composition of Capillary Specimens

• Mixture of arterial, venous, and capillary blood

– Higher proportion of arterial than venous especially if the area has been warmed

• Mixed with tissue fluid from surrounding tissues

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Tests that cannot be Collected by

Microcollection

Some examples

ESR

Coagulation Tests which require plasma

Blood cultures

Tests that require large volumes of serum or plasma –

depends on technology used

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Capillary Puncture Principles

• Order of Draw

– Blood gas specimens (CBGs)

– EDTA specimens

– Other additive specimens

– Serum specimens

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Capillary Puncture Equipment:

• Equipment should allow

• To puncture skin safely

• To collect the sample quickly and

efficiently

• Minimum of discomfort to the patient

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• Need general blood drawing equipment

– Lancet

– Antiseptic

– Microtubes or other collection containers (e.g.

capillary tubes, etc.)

– Gauze pad

– Bandages

– Sharp-safe disposal

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Lancets

Many different devices available

Simplest is hand-held lancet: a thin-flat piece of steel with a sharp point

Puncture dimensions controlled by width and depth of the point

Automated devices with various color-coded depths available

1.8 mm

2.0 mm

2.4 mm

3.0 mm

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Capillary Puncture Equipment

• Lancet/Incision Devices – Sterile, disposable, sharp-pointed or bladed instrument

– Punctures or cuts skin to obtain capillary blood specimen

– Designed for either finger or heel puncture

• Laser Lancet – Vaporizes water in skin to produce a small hole w/o. cauterizing

capillaries

– No risk of accidental sharps injury, no need for sharps disposal

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• Finger puncture lancets


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• Heel puncture lancets


• Microcollection Containers

– Small plastic tubes used to collect tiny amounts of

blood from capillary punctures

– Some come with narrow capillary tubes attached

– Have color-coded bodies or stoppers

– Markings for min/max fill levels

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• Microcollection containers

Capillary Puncture

Equipment

• Microhematocrit Tubes and Sealants

– Disposable, narrow-bore plastic or plastic-clad glass tubes with anticoagulant

• Ammonium heparin

– Fill by capillary action & hold 50 to 75 L

– One end of tube is sealed with plastic or clay sealants

– Used primarily for hematocrit determinations

• Used with a special centrifuge and reading mechanism to calculate hematocrit

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McCall & Tankersley: Instructor Resource Guide for Phlebotomy Essentials, 3rd ed., copyright Lippincott Williams & Wilkins, 2003

Chapter 10

Slide 11

Indications for performing skin puncture

• adults

no accessible veins

to save veins for

chemotherapy

clotting tendencies

home-testing

procedures

Capillary Puncture

Equipment Blood gas capillary tubes

• Different volume sizes according to

instrumentation

• Most common size is 100 µL with sodium

heparin

• Stirrers: tiny pieces of metal – fleas- inserted in

the capillary to facilitate mixing

• Magnet: moved back and forth along the

capillary tube pulling the fleas with it

• Plastic caps: to seal blood

• Transported on ice

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• Capillary blood gas collection equipment

Warming Devices

Warming increases blood

flow approx 7 times

More useful for infants

Heel-warming devices

available

Temp should not exceed

420C

Alternative: Towel or

cloth dampened with

warm water

McCall & Tankersley: Instructor Resource Guide for Phlebotomy Essentials, 3rd ed., copyright Lippincott Williams & Wilkins, 2003

Chapter 10

Slide 7

Skin Puncture Equipment (continued)

• Plastic/Clay Sealant

• Capillary Blood Gas

Collection

Equipment

• Micropipet Dilution

System

• Warming Devices

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Blood Draw volume Body wt in kg Max drawn in one blood draw Maximum drawn in a 30 day period

2.5% of total blood volume 5% of total blood volume

1 kg 2.5 ml 5.0 ml

2 kg 4.5 ml 9.0 ml

3 kg 6 ml 12 ml

4 kg 8 ml 16 ml

5 kg 10 ml 20 ml

6 kg 12 ml 24 ml

7 kg 14 ml 28 ml

8 kg 16 ml 32 ml

9 kg 18 ml 36 ml

10 kg 20 ml 40 ml

11 thru 15 kg 22 - 30 ml 44 - 60 ml

16 thru 20 kg 32 - 40 ml 64 - 80 ml

21 thru 25 kg 42 - 50 ml 84 - 100 ml

26 thru 30 kg 52 - 60 ml 104 - 120 ml

31 thru 35 kg 62 - 70 ml 124 - 140 ml

36 thru 40 kg 72 - 80 ml 144 - 160 ml

41 thru 45 kg 82 - 90 ml 164 - 180 ml

46 thru 50 kg 92 - 100 ml 184 - 200 ml

Greater than 50 kg 100 ml 200 ml

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For requests greater than the maximum draw, please contact

the attending physician for approval of additional amount.

http://www.phsa.ca/research/Documents/pediatric-blood-draw-guidance.pdf








STEPS IN PERFORMING

CAPILLARY PUNCTURE

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Capillary Puncture Steps

• First 4 Steps Are Same as for Venipuncture

– Step 1: Review & accession test request

– Step 2: Approach, identify, & prepare patient

– Step 3: Verify diet restrictions & latex sensitivity

– Step 4: Sanitize hands & put on gloves

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• Step 5: Position Patient

– Finger puncture: arm supported on firm surface,

hand extended & palm up

– Young child: held in lap of parent or guardian

– Infant heel puncture: supine with foot lower than

torso

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• Step 6: Select the Puncture/Incision Site

– General criteria

• Skin is warm, pink, normal color

• No scars, cuts, bruises, rashes, cyanosis, edema,

or infection

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Site Selection for Older Children and Adults

• Recommended site

– Central, fleshy portion of finger

• Palmar surface

• Distal segment of the middle or ring finger of the

nondominant hand

• Slightly to the side of center

• Perpendicular to the whorls of the fingerprint to allow

formation of a drop – otherwise the blood flows over

the finger

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• Recommended site & direction of finger puncture

Finger Puncture Precautions

• Do not puncture side or tip of finger

• Do not puncture parallel to the grooves of

the fingerprint

• Do not puncture the index finger

• Do not puncture the little finger

• Do not puncture fingers of infants or very

young children

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• Step 6: Select the

Puncture/Incision Site

Cont’d – Infants (shaded area)

• Plantar surface of heel, on

medial or lateral edge to

avoid bone damage (<2.4

mm deep)

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Skin Puncture Site Selection Criteria

• Cross section of a full term

infant’s heel:

• Capillaries at 0.35 mm

depth

• Pain fibers increase in

number below 2.4 mm

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Skin Puncture Site Selection Criteria

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High risk areas 1. AVOID Posterior

curvature –bone at 1

mm

2. Calcaneus (heel

bone) 2 mm below

the skin, can cause:

Osteomyelitis

Osteochondritis

Posterior curvature

Medial

Plantar Lateral

Plantar

Heel Puncture Precautions

Do not puncture deeper than 2.4 mm

Do not puncture through previous punctures

Do not puncture the area between imaginary boundaries

Do not puncture the posterior curvature of heel

Do not puncture in the arch

Do not puncture areas of the foot other than the heel

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• Step 7: Warm the Site if Applicable

– Warming increases blood flow up to sevenfold

– Essential for pH or blood gas specimens & recommended

for heelsticks

– Wrap site for 3 to 5 min. with a warm, moist washcloth,

towel, or diaper

• Step 8: Clean and Air-Dry Site

– Cleanse site with an antiseptic (70% isopropyl alcohol)

– Allow to air-dry

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• Clean and air-dry the site


• Step 9: Prepare Equipment

– Don gloves if not already on

– Select collection devices & place in easy reach

– Select new, sterile lancet/incision device

– Open packages in view of patient

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• Step 10: Puncture the Site and Discard

Lancet – Finger puncture

• Grasp patient’s finger between nondominant thumb & index

finger

• Place lancet device flat against skin in central, fleshy pad

– Heel puncture

• Grasp foot gently but firmly with nondominant hand

• Encircle heel by wrapping your index finger around arch, thumb

around bottom, & other fingers around top of foot

• Place lancet flat against skin on medial or lateral plantar surface

of heel

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Finger prick Site

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• Puncture the site and discard lancet


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• Step 11: Wipe Away the First Blood Drop

– First drop is typically contaminated with excess tissue fluid

• Position the site downward to enhance blood flow

• Apply gentle intermittent pressure to produce full drops of

blood


• Step 12: Fill and Mix Tubes/Containers in

Order of Draw

– Collect blood gases, slides, platelet counts, &

other hematology specimens first to avoid

clumping & clotting

– Collect other anticoagulant containers next &

serum specimens last

– Touch collection tube or device to drop of blood

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Collecting the samples

To make a blood film, touch the appropriate area of the slide to the drop

To fill a capillary tube, touch one end of the capillary to the drop, while holding it in a horizontal position. Seal it when full

To fill a microcollection container, hold it upright just below the blood drop – touch the edge/scoop to the drop, and let it trickle down the side of the tube. DO NOT SCOOP AGAINST THE SKIN. It can cause platelet clumping and hemolysis.

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• Fill and mix tubes/containers in order of draw


• Step 13: Place Gauze and Apply Pressure

– Keep site elevated

• Step 14: Label Specimen and Observe Special Handling

Instructions

• Step 15: Check the Site and Apply Bandage

– Do not bandage small children or babies

• Step 16: Dispose of Used and Contaminated Materials

• Step 17: Thank Patient, Remove Gloves, and Sanitize Hands

• Step 18: Transport Specimen to the Lab

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Special Capillary Puncture

Procedures

• Capillary blood gas specimen by heel puncture

• Neonatal bilirubin collection

• Newborn Metabolic screening (NMS)

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Special Capillary Puncture

Procedures

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• Newborn screening blood spot collection

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