CAPILLARY PUNCTURE

• Capillary Puncture


  Skin Puncture, Dermal Puncture, Microsampling - Obtaining drops of blood from puncturing or making an incision in the capillary bed
• Capillary Blood


  • Combination of both arterial and venous blood and some interstitial fluid and intracellular fluid
  • Capillary blood affects potassium
  • Capillary blood contains more arterial blood - Can be used for blood gas analysis (BGA)
• Preferred Sites


  • Lateral plantar heel surface (for newborns/babies)
  • Palmar surfaces of the fingers (3rd and 4th) (for more than 1 year old, better to use middle finger)
  • Plantar surface of the big toe
  • Earlobes (least site)
• Sites not recommended or should be avoided

  • Central arch area of an infants heel
  • Fingers of newborn or infant, 1 y.o (Less than 1 year old)
  • Thumb, index and 5th fingers (Thumb - has pulse, Index - normally used every day, more calloused, Pinky - very thin skin)
  • Fingers on the side of mastectomy
  • With scarred areas (Burns, fungal infection, etc)
• Indications for Capillary Puncture

  • Small amounts of blood are acceptable to be use for testing
  • Suitable for adult and older children with: Fragile veins, Unsuccessful venipuncture, Patient has thrombotic or clot-forming tendencies, Patient is apprehensive or has fear of needles, No accessible veins, POCT procedures (Point of care testing, Bedside, Diabetic patients)
  • Preferred method for infants and very young children (Infants have a small blood volume (anemia), Large quantities of blood removed can result to cardiac arrest, Venipuncture may damage veins and surrounding tissues, Puncturing deep veins can result to hemorrhage, venous thrombosis, infection, and gangrene, Restraining method can injure an infant or child, Preferred specimen for some tests (NBS - new born screening))
• Capillary puncture is not appropriate for patients who are dehydrated or have poor circulation to the extremities
• Person who can benefit with this method of collection

  • Pediatric children (sample volume limited, benefit the most)
  • Obese patients
  • Chemotherapeutic patients (Their vein easily collapse, Veins are reserved for chemotherapy)
  • Burn patients
• Order of Filling Microsampling

  • EDTA -> Other additive tubes -> Serum tubes
  • BGA samples first before EDTA
• Test that Cannot be Performed by Capillary Puncture

  • ESR
  • Coagulation studies
  • Blood cultures (Cannot be used for blood culture since it needs 5 ml (more volume, more bacteria detected, the better))
  • Tests that require large volumes of serum or plasma
• Equipment Needed for Capillary Puncture

  • Blood collection supplies and equipment (general)
  • Lancets/Incision device/Laser lancets
  • Microcollection containers
  • Microhematocrit tubes and sealants
  • Capillary Blood Gas equipment
  • Microscope Slides
  • Warming devices
• Lancet/Incision Devices


  Sterile and disposable, Sharp pointed or bladed instrument - Purpose: Incises/punctures the skin of the capillaries
• Lancet/Incision Devices


  • OSHA required lancet safety feature should have a permanently retractable blade or needle point to reduce risk of sharps injury
  • Length of lancet: 1.75 mm
  • Depth of incision: Infants and children: < 2.0 mm, Adults: <2.5 mm
  • Distance from skin surface to bone or cartilage: 1.5-2.4 mm
  • Punctures should not be made more than 2.5 mm deep for infants; for adults 2-3 mm deep
• Laser Lancets


  Perforating skin with a laser instead of sharp instrument - Advantage: No sharps involved, less risk of sharps injury, No need for needle/lancet disposal
• Microcollection containers


  • Microtubes - Special small plastic tubes used to collect the tiny amounts of blood obtained from capillary puncture, Color coded bodies or stopper, Markings for minimum and maximum fill levels (uL), Some have capillary tube attached, Can be used as a substitute for evacuated tubes in case of short draws but label that it is a venous blood
• Microhematocrit tubes and sealants

  • Microhematocrit tubes - Disposable, narrow-bore plastic or plastic-clad glass capillary tubes, Can hold 50 to 75uL, Used only for checking hematocrit, Cannot be used for CBC
  • Sealants - Plastic or clay, Used to seal one side of microhematocrit tube
• Capillary Blood Gas Equipment


  CBG collection tubes - long thin narrow-bore capillary tubes, 100mm in length, 100 uL capacity, Color coded band (green for sodium heparin), Stirrers - small metal fillings or small metal bars to mix the blood in the CBG collection tube properly, Magnet - mixing the specimen, Plastic caps - sealing of CBG tubes and maintaining anaerobic condition
• Microscope Slides


  Making blood films for hematology determinations, In case of malarial diagnosis
• Warming Devices


  Purpose: to increase blood flow in the site, especially in the heel of the newborn, Temperature that does not exceed 42°C, Towel or diaper dampened with warm tap water
• Capillary Puncture Procedure


  1. Review and accession test request

  2. Approach, identify, and prepare patient

  3. Verify diet restrictions and latex sensitivity

  4. Sanitize hands and put on gloves

  5. Position patient

  6. Select the puncture/incision site

  7. Warm site if applicable

  8. Clean and air-dry site

  9. Prepare equipment

  10. Puncture the site and discard lancet

  11. Wipe away the first drop of blood

  12. Fill and mix tubes/containers in order of draw

  13. Place gauze and apply pressure

  14. Label specimen and observe special handling instructions

  15. Check the site and apply bandage

  16. Dispose of used and contaminated materials

  17. Thank patient, remove gloves, and sanitize hands

  18. Transport specimen to the lab
• Positioning Patient


  • Adult: patient's arm supported on a firm surface with hand extended and palm up
  • Children: held in the lap by a parent or guardian, restrains child with one arm and holds the child
  • Infant: supine (lying face up) with foot lower than torso
• Selecting the Puncture/Incision Site

  • Best site: fingers of adults and heels of infants
  • Adult and Children older than 1yo: Palmar surface of the distal or end segment of the middle or ring finger of non-dominant hand, Site: central, fleshy portion, slightly to the side of center and perpendicular to the grooves in the whorls of the finger print, Do not milk after puncturing, Can be massaged before puncturing, Cutting should be perpendicular and not parallel to the lines of the fingerprint to get a good drop of blood
  • Infants: Heel (plantar surface of the heel, medial or lateral), Not to puncture the bone (osteomyelitis, osteochondritis)
• According to CLSI, capillary puncture must not be performed on the fingers or earlobes of newborns or other infants under 1 year of age
• Finger Puncture Precautions


  • Do not puncture fingers of infants and children under 1 year of age
  • Do not puncture fingers on the same side of mastectomy
  • Do not puncture parallel to the grooves or lines of fingerprint
  • Do not puncture the index finger
  • Do not puncture the side or very tip of the finger
  • Do not puncture the thumb
• Pain fibers increase in abundance below the capillary bed, so deeper punctures are more painful
• Heel Puncture Precautions


  • Do not puncture any deeper than 2.0mm
  • Do not puncture areas between the imaginary boundaries
  • Do not puncture in the arch and any areas of the foot other than the heel
  • Do not puncture severely bruises areas
  • Do not puncture the posterior curvature of the heel
  • Do not puncture through previous puncture sites
  • Do not puncture a site that is swollen
  • Safe portion of the heel: Median, Lateral, Heel, Plantar
• Warming the Site


  Warming the site dilates capillaries therefore increasing blood flow on the site, "Arterialized" - Used for blood gas analysis, 3-5 minutes with a washcloth, towel, or diaper, Commercial heel warming device, Caution: The temperature of the material used to warm the site must not exceed 42°C (108°F)
• Cleaning and Air-drying the Site

  70% isopropanol or 70% isopropyl alcohol (Not povidone iodine), Allow site to air dry to ensure maximum antiseptic action and minimize chance of alcohol contamination of the specimen, Natural drying - 30-60 seconds
• Preparing Equipment


  Depends on the tests requested, Place them within easy reach, Prepare in view of patient or guardian, New, sterile lancet/incision device - Intact packaging, Open in aseptic manner, Not touching/brushing any surface
• Puncturing the Site and Discarding Lancet

  Use sufficient pressure to keep device in place without deeply compressing the skin, Warn the patient about the puncture and activate release mechanism to trigger puncture, Remove the device immediately from the skin, Finger puncture: Grasp the patient's finger between the non-dominant thumb and index finger, Place the lancet device flat against the skin in the central, fleshy pad of the finger, slightly to the side of center and perpendicular to the fingerprint's whorls, In young children, it is usually best to grasp three or four of the child's fingers (pigilan), Heel puncture: Grasp the foot gently but firmly with the non-dominant hand
• New, sterile lancet/incision device

  • Intact packaging
  • Open in aseptic manner
  • Not touching/brushing any surface
• Puncture the site and discard lancet

  1. Use sufficient pressure to keep device in place without deeply compressing the skin

  2. Warn the patient about the puncture and activate release mechanism to trigger puncture

  3. Remove the device immediately from the skin
• Finger puncture


  1. Grasp the patient's finger between the non-dominant thumb and index finger

  2. Place the lancet device flat against the skin in the central, fleshy pad of the finger, slightly to the side of center and perpendicular to the fingerprint's whorls

  3. In young children, it is usually best to grasp three or four of the child's fingers (pigilan)
• Heel puncture


  1. Grasp the foot gently but firmly with the non-dominant hand

  2. Wrap index finger around the arch

  3. Thumb around the bottom

  4. Other fingers around the top of the foot

  5. Incision should be made at 90 degrees angle to create "gap" puncture

  6. Puncturing the central arch is painful and you cannot get much blood
• Wipe away the first drop of blood

  1. Downward position of the site to encourage blood flow

  2. Wipe away first drop of blood with a dry gauze pad

  3. Some POCT instruments may allow the use of first drop of blood
• Fill and mix tubes/containers in order of draw

  1. Downward to enhance blood flow

  2. Gentle, intermittent pressure

  3. Always follow correct order of draw

  4. Tap microtubes every now and then to let the blood settle at the bottom

  5. Invert 8-10 times (depends on the manufacturer)
• To fill a collection tube or device

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

  2. If making a blood film, touch the appropriate area of the slide to the blood drop

  3. A microhematocrit or narrow-bore capillary tube will fill automatically by capillary action

  4. To fill a microcollection container or microtube, hold it upright just below the blood drop
• Do not use a scooping motion against the surface of the skin and attempt to collect blood as it flows down the finger
• only touch the blood in the slide, not the skin
• put the microhematocrit tube horizontally or above but not below
• Place gauze and apply pressure

  1. Apply pressure until bleeding stops

  2. Keep site elevated