Capillary Puncture: Procedure and Indications

Capillary Puncture

• Involves obtaining blood drops by puncturing the capillary bed
• The sample obtained is a combination of arterial, venous, capillary blood, interstitial fluid and intracellular fluid
• The reference range for capillary blood differs from venous blood
• It is also called skin puncture, dermal puncture, or microsampling

Preferred puncture sites

• Lateral plantar heel surface
• Palmar surfaces of the 3rd or 4th fingers
• Plantar surface of the big toe
• Least preferred site is the earlobes

Sites to Avoid

• Central arch area of an infant's heel
• Fingers of newborn infants and children under 1 year of age
• Thumb, index, and 5th fingers
• Fingers on the side of a mastectomy
• Areas with scarring

Indications

• Use when small amounts of blood are sufficient for testing
• Use with patients with fragile veins, unsuccessful venipuncture, thrombotic tendencies or clot-forming tendencies, apprehension or fear of needles, no accessible veins
• Use for POCT (Point of Care Testing) procedures
• Use on infants with small blood volume and prevents cardiac arrest from large blood removal or damage to veins/surrounding tissues by venipuncture
• Avoid in patients with dehydration or poor circulation

Order of draw for microsampling

• EDTA tubes
• Other additive tubes
• Serum tubes
• Note that ESR, coagulation studies, blood cultures, and tests requiring large serum/plasma volumes cannot be performed using capillary puncture

Equipment Needed

• Blood collection supplies and equipment (general)
• Sterile and disposable lancets with sharp points or blades are required to puncture the skin and obtain small amounts of capillary blood
• Lancet selection aims for accurate collection while minimizing pain and tissue damage
• Finger or heel puncture are both acceptable
• OSHA-required lancet safety features include a permanently retractable blade or needle to prevent sharps injuries
• Lancet length should be 1.75 mm

Incision Depth

• Less than 2.0 mm for infants and children
• Less than 2.5 mm for adults
• The distance from the skin surface to bone or cartilage is 1.5-2.4 mm
• Punctures should not be made more than 2.5 mm deep for infants and 2-3 mm deep for adults

Laser Lancets

• Utilizes laser rather than sharp instruments
• It works by using a focused laser beam that cuts the skin without making contact
• This laser seals nerve endings and small blood vessels, making it almost painless with less bleeding
• Benefits include, reduces the risk of infection and needlestick injuries, and provides a consistent incision depth, which improves blood sample quality
• Usually used on a finger for adults and children 5 years of age and older

Microcollection containers

• Special small plastic microtubes that collect tiny amounts of blood from capillary puncture
• These are bullets that have Color-coded bodies or stoppers
• They are marked for minimum and maximum fill volumes in microliters, and includes the lot numbers and expiration date on tubes

Capillary puncture: Procedure

• Review and accession test request before starting procedure
• Verify diet restrictions as well as sensitivity to both latex
• Know how to identify and approach the patient, prepare them for the procedure
• Sanitize your hands
• Put on you gloves
• Place the patient in the right position
• Adults: Should be put on a firm surface that provides support, make sure it can extend its hand and palm upward
• Children: Hold the child on the lap of the parent or guardian, make sure to restrain him/her using one arm while the other has the child
• Best sites for adults are the fingers
• For infants it is the heel
• For adults and children older than one year you can use the palmar surface of the distal or end segment of the middle or ring finger of non-dominant hand
• The site must be located on the central, fleshy portion, slightly to the side of center and perpendicular to the grooves in the whorls of the finger print

Finger puncture precautions

• Do not puncture the finger of children below 1 year old
• Do not puncture the finger on the same side of the mastectomy
• Do not puncture parallely to the grooves or lines of the fingerprint
• Avoid puncturing the index finger, the side or very tip of the finger
• Pain fibers increase in abundance below the capillary bed, so deeper punctures are more painful

Heel puncture precautions

• Make sure to not puncture any deeper than 2mm
• Make sure not to puncture areas between imaginary boundaries
• Make sure to not puncture areas located on the foot other than the heel as well as severely bruised areas
• Also avoid puncturing the posterior curvature of the area as well as previously punctured or swollen sites

Warming a Site

• Warming the area is important as it will increase the blood flow on the site due to the dilation of the capillaries
• Arterialized happens to venous blood by replenishing the depleted oxygen
• This must be done by applying a washcloth, towel or diaper on the area for 3-5 minutes
• A commercial heel warming device can also be used, but make sure that the material used to warm the site must not exceed 420C

Cleaning a Site

• 70% isopropyl or 70% isopropyl alcohol should be used
• Povidone iodine must be avoided
• Make sure to let air dry on the area in order to provide maximum antiseptic action and decrease any alcohol substance that could contaminate the specimen
• Also note that alcohol may cause a stinging sensation, hemolysis glucose testing

Preparing equipment

• The equipment depends on the tests being requested, make sure to place it on an area that is easy to take
• Prepare it in view of the patient/guardian
• Make sure to select a new sterile lancet/incision device and unpack it during the process aseptically without touching or brushing any surface

Puncture Site and Discard Lancet

• Make sure to create sufficient pressure to keep the device in place but without deeply compressing or squeezing the skin
• Properly warn the patient of the puncture and activates the release mechanism to trigger the puncture
• remove the device from the skin right after

Finger Puncture

• You should grasp the patient’s finger between the non-dominant thumb and index finger
• Locate the lancet on the central part of the finger and perpendicular to the fingerprint’s whirls

Heel puncture

• Gently grasp the foot applying slight pressure via the non-dominant hand
• Wrap the index finger surrounding the arch, make sure that the thumb is placed at the bottom and that the other fingers are located at the top of the foot
• Create an incision at a 90 degree angle in order to create a “gap” puncture
• Maintain a downward position of the site in order for the blood flow to encourage
• Thoroughly wipe away away the first drop of blood using a dry gauze pad
• The first blood drop contains interstitial fluid, may contain alcohol, and produces hemolyzed sample
• Some POCT instruments allows for the use of the first drop of testing

Tubes/Containers: Draw Order

• Maintain a downward position of the site in order for the blood flow to encourage
• Gently apply intermittent pressure
• Be very careful not to strongly squeeze or milk the site as this may cause hemolysis and tissue fluid contamination may take place
• Follow the correct order of draw, you may need to tap the microtubes every now and then to let the blood settle at the bottom
• Invert it around 8-10 times and must pay attention to the fill levels, especially when the containers have anticoagulants

Special Skin Puncture Procedures

• Capillary Blood Gases are collected to analyze blood gases with the same site as routine capillary puncture
• Arterialize by warming a site around 5 to 10 minutes
• Always follow the same routine skin/capillary puncture
• A metal stirrer bar or metal filings are used for homogenous mixture
• They run through the full length of the tube several times to aid in mixing
• Handling: Perform on ice
• Collection and detection of an elevated bilirubin result is through Neonatal Bilirubin Collection
• A high level result is jaundice
• The sample can be collected through heel puncture, protected from light
• Collected using an amber-colored micro collection in order to protect the bilirubin result from the effect of ultraviolet light and should not be hemolyzed
• NBS: the state mandated testing of newborns for the presence of diseases that can cause mental handicaps

Blood Spot Collection

• Few drops obtained from heel puncture, blood drops adsorbed onto circles printed on a special type of filter paper
• Perform heel puncture, wipe away first drop of blood, filter paper close to heel, large drop of blood is applied to the center of the circle. Do not touch paper to the surface of the heel
• Blood must be continuously flowing
• Complete: circles should be filled well
• Incomplete: inability to perform all required tests and layering of blood leading to misinterpretation
• Perform this by heel puncture, wipe away first drop of blood and apply a large drop of blood in the center of the circle
• Avoid touching filter papaer with or without gloves
• Keep away from any object or substance before, during or after specimen collection
• Perform is by placing it under a an elevated area and apply hortizontal pressure away from heat/sunlight
• Make sure to not stack together the non-dried pieces
• Allow the specimen to allow dry
• Dispatch specimen to testing facility
• Key point: if blood film or smear is collected from the EDTA specimen it mus be don within 1 hour of collection

Steps for Blood flim/smear prepartaion

1. Perform capillary puncture
2. Wipe away the first drop of blood
3. Touch the slide the next drop of blood
4. Center the blood drop on the frosted side, with a dimaeter of 1-2mm
5. Hold the blood crop slide between the dominant hand
6. Push the spreader slide away from the top in a smooth manner, allow the blood to push past the other side
7. Place the drop of blood for the second smear on the spreader slide
8. apply pressure on the area
9. In pencil, label the frosted blood slides by writing the patient information on the frosted area
10. Air dry the blood sims
11. Thank the patient
12. Tranport the specimen to the laboratory

Unacceptable Blood Smears

• The blood smear does not have correct proportions of the slide
• The blood smear has jagged ends
• The blood smear transitions from thick to thin unevenly

Problems with Blood Smear preparations

Absence of feather: Spreader slide was lified early Holes: Unclean slide used Ridges: High pressure was aplied Too thick: Blood was too big Too shrot: Little amoun of balood

Thick Blood Smear Preparation

• Used to detect malaria, a large drop is blood should be positioned at the center of a glass slide
• It is the covered with a coverslip utnil it has a dime size and should be dried for 2 hour before staining
• Usually perform staining with Giemsa stain