CHAPTER 10

Capillary specimens

Any specimen obtained through capillary, dermal, or skin puncture

Lancets

device used for capillary puncture

Designed for only one use, have sterile blades or points.

Available in a range of lengths and depths to accommodate various specimen collection requirements. Selection depends on the age of the patient, collection site, volume of specimen required, and the puncture or incision depth needed to collect an adequate specimen

Different types either for finger or infant heel puncture- must have OSHA required safety features

Collecting small amounts of blood by capillary puncture is called

Microcollection

Microtubes

Special small plastic tubes used to collect the tiny amounts of blood obtained from capillary punctures. They are often referred to as bullets because of their size and shape.

Some come fitted with narrow plastic capillary tubes to facilitate (make process easier) specimen collection

Others have an attached or removable scoop or funnel device to assist with blood collection

If you are using microtubes for venous blood collection (if acceptable) make sure you

Write down that it’s venous blood on the label so it doesn’t get confused with capillary blood because most microtubes are capillary specimens

Microhematocrit tubes and sealants

Disposable narrow-bore plastic or plastic-clad glass capillary tubes that fill by capillary action and typically hold 50-70microliters of blood.

They are used primarily for manual hematocrit (HCT) also called packed cell volume (PCV) determinations

The tubes come coated with ammonium or sodium heparin for collecting hematocrit tubes directly from a capillary puncture or non-additive tubes to be used when a hematocrit is prepared using blood from lavender EDTA tube

Heparin tubes typically have a

Red or green band on one end

Non-additive tubes have a

Blue band

Smaller microhematocrit tubes designed for use with special microcentrifuges, such as

Those available from StatSpin inc. require as little as 9 µL of blood and are often used in infant and children anemia screening programs, and pediatric clinics

What is used to seal one end of microhematocrit tubes

Plastic, clay, or wax sealants that come in small trays

Capillary blood gas equipment

Used to collect capillary blood gas (CBG) specimens

CBG equipment: collection tubes

Long, thin, narrow-bore tubes

They are normally plastic for safety and are available in different sizes to accommodate volume requirements of various testing instruments.

Most common CBG tubes are 100 mL in length with a Capacity of 100 Microliters.

The inside of the tube is coded with heparin, Typically identified with a green band on the tube

CBG equipment: stirrers

Small metal bars that are inserted into the tube after the blood is collected to aid and mixing the anticoagulant

CBG equipment: magnet

Used to mix the specimen after both ends of the tube have been sealed. The magnet typically has an opening in the center or side so that it can be slipped over the capillary tube and move back-and-forth along the tube length, pulling the metal stirrer with it and mixing the anticoagulant with the blood

CBG equipment: plastic caps

Are used to seal capillary blood gas tubes and maintain anaerobic conditions in the specimen. Capillary blood gas tubes typically come with their own caps

Warming devices

Warming the site is important when performing heal punctures on newborns.

To avoid burning the patient the devices provide a uniform temperature that does not exceed 42°C.

A towel or diaper dampened with warm tapwater can also be used to wrap a hand or foot before skin puncture. However, care must be taken not to get the water so hot that it’s scalds the patient.

Capillaries

Blood capillaries are the tiny vessels that connect the arterial and venous systems and where the exchange of gases and nutrients takes place

The capillary bed in the dermis of the skin is where blood for laboratory testing is obtained

Capillary blood is not the same as venous Blood and is not an acceptable specimen for some tests.

Capillary puncture risks

Although mostly minor, there are risks associated with capillary puncture

Bruising, hematoma, infection, puncture site calcification, and scarring

Blood obtained by puncturing the capillary bed is a mixture of

Arterial, venous, and capillary blood, along with Interstitial fluid (Tissue fluid from spaces between the cells) and intracellular fluid (Fluid within the cells)

Because arterial blood enters the capillaries under greater pressure than the venous pressure-

Capillary blood contains a higher portion of arterial blood

Capillary blood more closely resembles arterial blood than venous blood in composition.

Warming increases

Arterial flow into the area

Reference values

Because the composition of capillary blood differs from that of venous blood, reference (normal) values may also differ

Most differences are minor, though clinically significant differences in some analytes have been reported.

Glucose is higher in

Capillary blood

Bilirubin, calcium, chloride, sodium, and total protein (TP) concentrations are

Significantly lower in capillary blood

A properly collected capillary specimen can be a practical Alternative to venipuncture when-

Small amounts of blood are acceptable for testing

Reasons for capillary puncture in children and adults

•veins are fragile, difficult to access, or must be saved for other procedures, such as chemotherapy

• Several unsuccessful venipuncture Have been performed

• The patient has burns or scars

• The patient is apprehensive or has an intense fear of needles

• The patient is extremely overweight and veins are difficult to find

• There are no accessible veins

• Blood is being obtained for a point of care testing procedures, such as glucose

Reasons infants and young children need capillary puncture

• Infants have a small blood volume and removing Quantities of blood can lead to anemia

• Large quantities removed rapidly cause cardiac arrest. Life may be threatened if more than 10% of a patient’s blood volume is removed at once or over a very short period

• Obtaining blood from infants and children by venipuncture is difficult and may damage veins

• An infant or child can be injured by the restraining method used while performing venipuncture

• Capillary blood is the preferred specimen for some test such as newborn screening test

Tests that cannot be collected by capillary puncture

Erythrocyte sedimentation rate methods, coagulation studies that require plasma specimens, blood cultures, and tests that require large volumes of serum or plasma.

Order of draw

1. Blood gas specimens

2. EDTA specimens

3. Other additive specimens

4. Serum specimens

Puncturing the site through capillary puncture releases tissue

Thromboplastin which activates the coagulation process in the blood drops.

Specimens must be collected quickly to minimize the effects of platelet clumping and micro clot formation and to ensure that an adequate amount of specimen is collected before the site stops bleeding

Specimens that are most affected by clotting must be collected

First

Capillary blood gas is collected first to minimize exposure of the blood to air and because

Clots in the specimen are unacceptable.

However, capillary blood gas is often collected separately and is rarely part of a Typical capillary collection.

Hematology specimens (EDTA/lavender) are collected 2nd because

Clotting in these specimens is also unacceptable

When capillary blood gas is not part of the collection, hematology specimens are collected first because of all the micro tubes collected, they are the most affected by the clotting process

Other additive specimens are collected

After EDTA specimens.

They can also be affected by clotting, but not to the extent that hematology specimens are affected.

Serum specimens are collected last because

They are supposed to clot

Capillary specimens can be obtained from adults and children-

Over the age of 1 year by puncture of finger

Heelsicks are for

Infants less than one year

Steps 1-5 are the same across the board for all needle inserts

Capillary puncture-Step 6: position the patient

Finger stick- Patient should be sitting, ask the patient which hand to use and select the non dominant hand of possible. Position the hand down to encourage blood flow.

Heelstick- infant should be supine (lying face up) with the foot lower than to torso so the force of gravity can assist blood flow. Coordinate any needed changes to the bassinet, incubator, or phototherapy lights So that everything is returned to the way it was prior to specimen collection.

Step 7: select the puncture site

Site selection criteria include selecting a site that is warm, normal color, and free of scars, bruises, or rashes.

Should not be cyanotic (bluish in color usually from a shortage of oxygen in the blood), edematous (Swollen with fluid), infected, or a recent puncture site.

Accumulated tissue fluid from swollen or previously punctured sites can contaminate the specimen and negatively affect test results, can also spread undetected infection

Recommend site for finger stick

Palmer surface of the distal segment of the middle or ring finger of the non-dominant hand. Fingers on the non-dominant hand are typically less calloused.

The puncture site should be in the central fleshy portion of the finger, slightly to the side of center and perpendicular to the grooves of the fingerprint

Do not puncture fingers of infants 6 to 12 months old unless the infant weighs more than

10 kg and the puncture depth does not exceed 1.5 mm

Earlobes

Avoid puncturing these on older infants and children. Do not also puncture toes on infants or toes on adults unless it’s the big toe

Infant heel puncture

Recommended for collection of capillary puncture specimens on infants less than one year. Puncture in site not near bone

Puncture of the bone can cause painful

Osteomyelitis (Inflammation of the bone marrow)

Osteochondritis (inflammation of the bone and cartilage due to infection)

What depth provides adequate blood flow without risking bone injury

2 mm

The safest areas for heel puncture are the most medial and lateral portions of the planter surface of the heel

Punctures and other areas risk bone, nerve, tendon, and cartilage injury

Step 8: warm the site

Warming increases arterial blood flow up to seven times and does not significantly alter tests results other than PaO2

Increased blood flow makes specimens easier and faster to obtain and reduces the tendency to compress or squeeze the site which can contaminate the specimen with tissue fluid and hemolyze red blood cells

Warming the site is considered essential when collecting capillary pH or blood gas specimens

Warm for 3-5 min with a warm washcloth, towel, diaper, or warming device

Arterialized

A specimen obtained from a warm site is described as this

Step 9: gather supplies and equipment

Gather supplies and equipment in advance to help ensure that the correct equipment is ready and supplies are within reach for the procedure.

Step 10: clean and air dry the site

Clean the collection site with an antiseptic before puncture so that the skin flora do not infiltrate the puncture wound and cause infection. CLSI recommends 70% isopropanol.

Let it air dry completely or else it could cause a stinging sensation, Rapid hemolysis, or interfere with glucose testing

Step 11: prepare equipment aseptically

Verify Lancet sterility. Keep things sterile and open needle packaging cautiously

Step 12: grasp the finger or heal firmly

To prepare for the puncture, use your non-dominant hand to grasp the finger or heal firmly to prevent sudden movement by the patient. Hold the lancet between your thumb and index fingers of your dominant hand and hold the patients finger or heel

How to hold finger for fingerstick

Grasp the patient’s middle or ring finger between your non-dominant thumb and index finger. Hold it securely in case of sudden movement.

Holding heels for heelsticks-

Grasp the foot gently but firmly with your non-dominant hand. Encircle the heel by wrapping your index finger around the arch and your thumb around the bottom. Wrap the other fingers around the top of the foot.

Step 13: position the lancet, puncture site, and discard the lancet

Place the lancet flat against the skin in an appropriate area. Use significant pressure to keep it in place without deeply compressing the skin. (pressing too hard can result in a puncture that is deeper than intended)

Warn the patient of the impending puncture

Remove the device from the skin following puncture and immediately discard it in a sharps container

Step 14: lower the finger or heel, And apply gentle pressure until a blood drop for forms

Position downward and apply gentle pressure to the heel or finger To encourage blood flow.

Step 15: wipe away the first blood drop

Wipe away with clean gauze

The first drop is typically contaminated with excess tissue fluid and may contain alcohol residue that can hemolyze the specimen or keep the blood from forming a well-rounded drop.

Isopropyl alcohol can cause errors in glucose testing

Step 16: fill and mix tubes/containers in order of draw

Continue to position the site downward to enhance blood flow and continue to apply gentle pressure until a second drop forms

Collect subsequent blood drops using micro tubes or other devices appropriate for the ordered test.

To fill a collection tube or device-

Touch it to the drop of blood formed on the surface of the skin

Collect slides, platelet counts, and other hematology specimens first to avoid the effects of platelet clumping and clotting. Collect other anticoagulant micro tubes next and serum tubes last

If making a blood film

Touch the appropriate area of the slide to the blood drop

A microhematocrit or narrow-bore capillary tube will fill-

Automatically by capillary action, which is the ability of a liquid to be automatically drawn into a narrow space or tube.

To fill this type of tube, hold it in a horizontal position or with one end at a slight downward angle toward the blood drop. Touch the end of the tube to the blood drop without touching the skin.

While maintaining contact with the blood drop, you may need to lower the opposite end of the tube slightly and bring it back into position now and then as it fills

Do not remove the tube from the drop or continually hold or tip the opposite end below the site, this can result in air spaces in the specimen that can cause inaccurate test results

When the tube is full, plug the opposite end (dry end) with clay, a cap, or other sealant

To fill a microtube-

Hold it upright just below the blood drop. Touch the tip of the tubes collector device or “scoop” to the drop of blood and allow the blood to flow freely down the inside wall of the tube.

Touch only the blood drop and not the surface of the skin, this allows blood to be collected before it runs down the surface of the finger or heel

When filled to the level required, immediately seal microtubes with the covers provided. Mix additive microtubes by gently inverting them 8 to 10 times or per manufacturers instruction

If blood flow stops, and you are unable to collect a Sufficient specimen, The procedure may be repeated at a new site with a new lancet

Step 17: place gauze, apply pressure, and elevate the site

Use clean gauze pad until bleeding stops. Elevate the site while applying pressure.

Elevate an infant foot above the body while pressure is applied

Step 18: label specimens, Confirm labeling information, And prepare specimens for handling and transport

Label specimens with the appropriate information immediately after specimen collection. Include type and source of specimen, according to facility policy. Label before leaving the patient side or dismissing an outpatient. Verify labeling with the patient or parent or ID band.

Microhematocrit tubes can be placed in a

Non-additive tube or an appropriately sized aliqout tube for transport with Identifying information written on the transport tube label for transport according to laboratory protocol

Step 19: check the site and apply a bandage

Examine the site for 5 to 10 seconds to verify that the bleeding has stopped. If bleeding persists beyond five minutes, notify the patient’s physician or appropriate health healthcare provider. If the bleeding has stopped, apply a bandage

Do not apply bandages/gauze to infants and children under the age of two because

They pose a choking hazard, skin tear/irritation hazard, or cut off circulation if gauze wrap is applied

Step 20: discard used materials, thank the patient, parent, or guardian and dismiss outpatient

Equipment packaging and bandage wrappers can be discarded in a regular trashcan and discard contaminated items in a biohazard container

Prompt delivery to the lab protects specimen integrity and is typically achieved by

Personal delivery, transportation via a pneumatic tube system, or a courier service

The most common heel stick procedures on infants are the collection of

Capillary blood gases, bilirubin specimens, and newborn screening specimens.

Capillary collection can also be used to collect blood smears for a manual Hematology test called a differential.

Special thick blood smears can also be collected by capillary puncture to detect malaria organisms

Capillary blood gas