Alkuino, Reah Jayzel G.

“CAPILLARY PUNCTURE”
ALKUINO, REAH JAYZEL G.

BMLS 1B
I. INTRODUCTION
A. DEFINITION
In phlebotomy, dermal puncture is a method where the blood sample is collected from the capillary,
which contains capillary blood that is a mixture of venous blood and arterial blood which also contain small
interstitial and intracellular. Also, the other term for dermal puncture is “micro collection” which blood is
usually drawn from the finger or heel of the patient. It is usually done in the laboratory due to modernized
method of blood specimen collection such as Point-of-care testing (POCT) and micro sampling. In addition,
Blood collected by dermal puncture comes from the capillaries, arterioles, and venules.
B. APPLICATION
Dermal puncture is the method of choice for blood collection on infant or children younger than 2
years to avoid causing anemia because smaller amounts of blood can be collected. Deep vein puncture in
children is dangerous and may cause complications. Infant’s large superficial vein is difficult to locate.
Also, capillary specimen such as capillary blood gas analysis and new born screening is required for infant’s
test.
In adults, it is advantageous for patients who are required frequent blood test or serial monitoring,
required small samples and POCT, are burned or scarred, are receiving IV or chemotherapy, have
thrombotic tendencies, are geriatric with fragile veins, are obese, are apprehensive, have inaccessible veins,
or are diabetic, inaccessible vein of an obese patient.
C. DERMAL PUNCTURE EQUIPMENT
There are various types of capillary puncture equipment that can be used such as lancets, capillary
tube and micro collection tube container. First, lancets are a dermal puncturing device in the skin by
inserting blade or needle vertically into the tissue. Lancets’ needle length should be 1.75 mm and the
incision width is not larger 2.5mm in order to produce sufficient blood during collection. Second, capillary
tube frequently referred to as microhematocrit tubes, are small tubes used to collect approximately 50 to 75
μL of blood for the primary purpose of performing a microhematocrit test. The tube length is 70 to 75 mm
and the bore is 1.2 mm. The filled proportion should be 0.05 ml, unfilled should be 2 cm and the clay seal
should 4 to 6 mm. Lastly, Micro collection tube is a tube designed to hold 600 μL of blood sample. It comes
with collection scoop and plastic capillary tube. Separation and mixing are enhanced with plastic beads and
separating gel.
II. SPECIMEN COLLECTION
A. SITE SELECTION
The sites for dermal puncture are commonly at the fingers and heel of the patient. Finger puncture
is located at the distal portion the 3rd and the fourth finger usually in the non-dominant hand it should be
perpendicular to the grooves of the finger print and the and the hand should be positioned on a plantar
surface and fingers pointed downward. Moreover, heel puncture has more tissue than fingers in infants that
is younger than 1 year. The site for Heel puncture must be lateral and medial side plantar surface of the
heel. It should not exceed more than 2 mm because it may cause osteomyelitis.
B. PROCEDURE
The following are the step-by-step procedure of dermal puncture:
1. Patient identification and preparation: (requisition form, verbal identification, and ID

band). Patient’s position must be seated or lying down with the hand supported on a firm surface, palm up,
and fingers pointed downward for finger sticks. Heel sticks, infants should be lying on the back with the
heel in a downward position.
2. Appropriate incision device selection and puncture site: heel sticks,

infants should be lying on the back with the heel in a downward position.
3. Warming of puncture site: 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.
4. Proper disinfection of the puncture site: cleansed with 70% isopropyl alcohol,
using a circular motion and let dry.
5. Wipe away the first drop of blood: to get rid of contaminated blood.
6. Avoid milking, scooping or scraping of the puncture site
7. Collect specimen quickly (less than 2 minutes): to avoid blood coagulation.
8. Fill the correct volume of collection containers
9. Proper mixing: to properly mix the additives to the blood specimen.
10. Properly label specimen: to avoid confusion and prevent misidentification of the specimen.
C. ORDER OF DRAW
The importance of Order of draw is to avoid cross-contamination of the sample by additives found
in different collection tubes. The following are the order of draw:
Single Collection of blood for Complete Blood Count (CBC)

1. Blood smear
2. Ethylenediaminetetraacetic acid (EDDTA) microtainer
Multiple Collection:
1. Capillary blood gas
2. Blood smear
3. EDTA microtainer
4. Other anticoagulant microtainers
5. Serum microtainers
III. CONTRAINDICATIONS OF DERMAL PUNCTURE
Do Not Perform Capillary Puncture If:
 Patients with poor circulation.

 Patient is severely dehydrated.
 Coagulation studies requiring plasma.
 Tests requiring large volume of blood. (ESR & Blood Culture)
 Swollen, bruised, infected or already been punctured.
IV. ADVANTAGE AND DISADVANTAGE OF DERMAL PUNCTURE

A. CHILDREN
Advantage
 Decreases the occurrence of anemia due to blood draw

 Less traumatic experience
 Collection sites can be changed so that the risk of scarring and pain is lessened.
 Doesn’t require deep vein withdrawal
Disadvantage
 Not all test can be run on capillary sample

 Only a limited amount of blood can be drawn using this method
 High chances of Excessive bleeding
 High chances of infection
 Capillary blood sampling may cause inexact results
B. ADULT
Advantage
 Test can be done at home

 Blood draw site choice due to fragile vein
 Blood can be drawn on obese patient
 Used during serial monitoring
 Requires small blood sample and POCT
Disadvantage
 Capillary blood sampling may result in inaccurate results, such as falsely elevated sugar,
electrolyte, and blood count values.
 Patients may feel faint after any type of blood drawing.
 Infection and excessive bleeding may occur
 Limited test can be performed
V. BLOOD SMEAR PREPARATION
A. PROCEDURE
1. Place the second drop of blood in the center of glass slide near the frosted edge. The drop should be 1-2
mm in diameter.
2. Place the spreader slide with a clean smooth edge in front of the blood at 30-40-degree angle inclined
over the blood.
3. Slide the back of the spreader to the edge of the drop of blood allowing the blood to spread across the
end.
4. Lightly push the spreader maintaining the angle and not applying pressure on the spreader.
5. Terminate at around 0.5 mm inch before the edge of the slide.
6. Label by writing the patient’s information on the frosted area using a pencil.
B. QUALITIES OF GOOD SMEAR

1. The film is two thirds to three fourths the length of the slide.
2. The film is finger shaped, very slightly rounded at the feather edge, not bullet shaped.
3. The lateral edges of the film are visible.
4. The film is smooth without irregularities, holes, or streaks.
5. The film progresses from being thick at the point of origin to thin with a uniform edge at the termination
point.
6. Should have a lightly feathered edge without streaks.
C. DISADVANTAGE OF ERRORS ON BLOOD SMEAR

The following are the effects of error on blood smear:
Uneven distribution of blood (ridges)
 Increase pressure on the smear slide

 Movement of the spreader slide not continuous
 Delay in making slide after drop is placed on slide
Holes in the smear
 Dirty slide
 Contaminated with glove powder
No feathered edge
 Spreader slide not pushed the entire length of the smear slide.
Streaks in the feathered edge
 Chipped or dirty slide.

 Spreader slide not placed flush against the smear.
 Pulling the spreader slide into the drop of blood so that the blood is pushed instead of pulled.
 Drop blood starts to dry out owing to delay in making smear.
Smear too thick and short
 Drop of blood is too big.

 Angle of spread slide is greater than 40 degrees.
Smear too thin and long
 Drop of blood is too small.

 Angle of spreader slide is less than 30 degrees.
 Spreader slide pushed too slowly.
VI. SPECIAL DERMAL PUNCTURE

A. NEWBORN SCREENING
A test for genetic, metabolic, hormonal and functional disorders that can lead to mental retardation,
physical disabilities or death. Usually collected after 24 hours of life but not later than 3 days from delivery.
 Neonatal intensive care unit: tested 7 days of age.
NEWBORN SCREENING PROCEDURE

• Heel stick is performed in routine manner and a large drop of blood is then applied directly onto a filter
paper circle.
• Phlebotomists must be careful not to touch nor contaminate the sample.
• To obtain an even layer of blood, only one large free-falling drop should be used to fill a circle. Each
circle must be filled for testing.
• Air dry in a suspended horizontal position at room temperature away from direct sunlight.
B. NEW BORN BILIRUBIN
The Collection of New born bilirubin is at timed interval. Also, one of the most important and
frequent tests in newborn for monitoring of hemolytic disease of the newborn (HDN).
Related Key words:
• Kernicterus – accumulation of bilirubin in the brain.
• Jaundice – yellowing of the skin due to accumulation of bilirubin at the body.
C. CAPILLARY BLOOD GASES
The preferred sample for blood gases is the Arterial blood (oxygen and carbon dioxide content) and
pH levels in adults. In Neonatal blood gases, the arterialization of blood is enhanced by warming the
puncture site. special capillary tube with metal stirrers (flea) with cover on each end is used to collect the
sample.
D. MALARIA SMEAR
Malaria Smear is a test performed for quantification for malaria parasite. A drop of blood is placed
at the center of the slide and is spread using an applicator stick until it is about a size of a dime. It is air
dried for hours and apply stain. For the malaria parasite identification, two to three smears are prepared to
run the test. Also, thick smear confirms the presence and absence of malarial parasite while the thin smear
is for the identification of specific malarial parasite.
REFERENCES
• The Phlebotomy Textbook, Strasinger & Di Lorenzo, 3rd Edition
• Clinical Hematology: Theory and Procedure, Turgeon, 5th Edition
• Rodaks Hematology: Clinical Principles and Applications, 5th Edition
• Henry’s Clinical Diagnosis and Management by Laboratory Methods, 22nd Edition

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“CAPILLARY PUNCTURE”

C. DERMAL PUNCTURE EQUIPMENT

II. SPECIMEN COLLECTION

The following are the step-by-step procedure of dermal puncture:

1. Patient identification and preparation: (requisition form, verbal identification, and ID

2. Appropriate incision device selection and puncture site: heel sticks,

6. Avoid milking, scooping or scraping of the puncture site

7. Collect specimen quickly (less than 2 minutes): to avoid blood coagulation.

8. Fill the correct volume of collection containers

9. Proper mixing: to properly mix the additives to the blood specimen.

Single Collection of blood for Complete Blood Count (CBC)

 Patients with poor circulation.

IV. ADVANTAGE AND DISADVANTAGE OF DERMAL PUNCTURE

 Decreases the occurrence of anemia due to blood draw

 Not all test can be run on capillary sample

 Test can be done at home

B. QUALITIES OF GOOD SMEAR

C. DISADVANTAGE OF ERRORS ON BLOOD SMEAR

 Increase pressure on the smear slide

 Chipped or dirty slide.

 Drop of blood is too big.

 Drop of blood is too small.

VI. SPECIAL DERMAL PUNCTURE

 Neonatal intensive care unit: tested 7 days of age.

NEWBORN SCREENING PROCEDURE

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