Dermal Puncture

Question 1

Blood collected by dermal puncture comes from the capillaries, arterioles, and venules. The method of choice for collecting blood from infants and children younger than 2 years

Answer 1

Dermal (capillary or skin) puncture

Question 2

Certain tests require capillary blood, such as newborn screening tests and capillary blood gases.

Question 3

Hemolysis may occur in dermal puncture for the following reasons:

Answer 3

Excessive squeezing of the puncture site (“milking”)

Newborns have increased numbers of red blood cells (RBCs) and increased RBC fragility

Residual alcohol at the site

Vigorous mixing of the microcollection tubes after collection

Question 4

Referred as microhematocrit tubes. Collect approximately 50 to 75 µL of blood. Tubes are designed to fit into a hematocrit centrifuge and its corresponding hematocrit reader

Answer 4

Capillary tube

Question 5

Provide a larger collection volume and present no danger from broken glass.

Answer 5

Microcollection Tubes

Question 6

Must be seated or lying down with the hand supported on a firm surface, palm up, and fingers pointed downward for fingersticks. For heelsticks, infants should be lying on the back with the heel in a downward position.

Answer 6

Patient Position

Question 7

Primary dermal puncture sites:

Answer 7

Heel
Distal segments of the third and fourth fingers

Question 8

Acceptable areas for heel puncture:

Answer 8

Medial and lateral areas of the plantar(bottom) surface of the heel.

Question 9

Are performed on adults and children over 1 year of age.

Answer 9

Finger Puncture

Question 10

Finger Puncture Sites:

Answer 10

Fleshy areas located near the center of the third and fourth fingers on the palmar side of the nondominant hand.

Question 11

Warming dilates the blood vessels and increases arterial blood flow.

Question 12

Warming the Site

Answer 12

Moistening a towel with warm water (42°C) or activating a commercial heel warmer and covering the site for 3 to 5 minutes effectively warms the site.

Use caution in moistening the towel to ensure the water temperature is not greater than 42°C to avoid burning the patient. Site should not be warmed for longer than 10 minutes or test results may be altered.

Question 13

Cleansing the Site

Answer 13

Selected site is cleansed with 70% isopropyl alcohol, using a circular motion.

The alcohol should be allowed to dry on the skin for maximum antiseptic action, and the residue may be removed with gauze to prevent interference with certain tests.

Question 14

Performing the Puncture

Answer 14

The heel or finger should be well supported and held firmly, without squeezing the puncture area.

Massaging the area before the puncture may increase blood flow to the area.

Question 15

Performing Heel Puncture

Answer 15

The heel is held between the thumb and index finger of the nondominant hand, with the index finger held over the heel and the thumb below the heel

Question 16

Performing Finger Puncture

Answer 16

The finger is held between the nondominant thumb and index finger, with the palmar surface facing up and the finger pointing downward to increase blood flow.

Question 17

Puncture Device Position

Answer 17

1. Choose a puncture device that corresponds to the size of the patient.
2. Remove the trigger lock if necessary.
3. Place the puncture device firmly on the puncture site.
4. Do not indent the skin when placing the lancet on the puncture site.
5. The blade of the puncture device should be aligned to cut across (perpendicular to) the grooves of the fingerprint or heel print.
6. Depress the lancet release mechanism and hold for a moment, then release.
7. Pressure must be maintained because the elasticity of the skin naturally inhibits penetration of the blade.
8. Removal of the lancet before the puncture is complete will yield a low blood flow.

Question 18

Sample Collection

Answer 18

The first drop of blood must be wiped away with a clean gauze

When collecting microsamples, even a minute amount of contamination can severely affect the sample quality.

Blood should be freely flowing from the puncture site as a result of firm pressure
and should not be obtained by milking of the surrounding tissue, which will release tissue fluid.

Alternately applying pressure to the area and releasing it will produce the most satisfactory blood flow.

Tightly squeezing the area with no relaxation cuts off blood flow to the puncture
site.

Question 19

Capillary Tubes and Micropipette

Answer 19

To prevent the introduction of air bubbles, capillary tubes and micropipettes are held horizontally while being filled.

Place the end of the tube into the drop of blood and maintain the tube in a horizontal position to fill by capillary action during the entire collection.

Removing the microhematocrit tube from the drop of blood causes air bubbles in the sample.

The presence of air bubbles limits the amount of blood that can be collected per tube and will interfere with blood gas determinations.

When the tubes are filled, they are sealed with sealant clay or designated plastic caps.

Recommended tubes are plastic or coated with a puncture-resistant film.

When using a sealant tray, place the end that has not been contaminated with blood into the clay taking care to not break the tube.

Remove the tube with a slight twisting action to firmly plug the microhematocrit tube.

Question 20

Microcollection Tubes

Answer 20

Microcollection tubes are slanted down during the collection, and blood is allowed to run through the capillary collection scoop and down the side of the tube.

The tip of the collection container is placed beneath the puncture site and touches the
underside of the drop.

Gently tapping the bottom of the tube may be necessary to force blood to the bottom.

When a tube is filled, the color-coded top is attached.

Tubes with anticoagulants should be inverted 5 to 10 times or per manufacturer’s instructions.

If blood flow is slow, it may be necessary to mix the tube while the collection is in progress.

It is important to work quickly, because blood that takes more than 2 minutes to collect may
form microclots in an anticoagulated microcollection container.

Question 21

Order of Collection

Answer 21

Blood gases
Blood smear
EDTA tubes
Other anticoagulated microcollection tubes
Serum microcollection tubes

Question 22

Dermal puncture may be required in many adult patients, including:

Answer 22

Burned or scarred patients

Patients receiving chemotherapy who require
frequent tests and whose veins must be reserved for therapy

Patients with thrombotic tendencies

Geriatric or other patients with very fragile veins

Patients with inaccessible veins

Obese patients

Apprehensive patients

Patients requiring home glucose monitoring and point-of-care tests

Question 23

Blood collected by dermal puncture comes from the capillaries, arterioles, and venules

Question 24

Blue band capillary tube

Answer 24

Plain / Non-heparinized

Question 25

Red band capillary tube

Answer 25

Coated with ammonium heparin / Heparinized

Question 26

Patient Identification

Answer 26

Requisition form
Verbal Identification
ID band