PMLS LAB LECTURE 1

• Capillary Sampling


  Sampling from a finger, heel or (rarely) an ear lobe, may be performed on patients of any age, for specific tests that require small quantities of blood
• Capillary sampling


  • Commonly used in pediatric patients
  • Normally recommended for pediatric patients, especially newborns and infants up to 12 months, because their veins are small and not well developed, creating a considerable risk of permanent damage
  • In some cases, capillary collection is not feasible or possible owing to type or volume requirements of tests ordered; a venipuncture is necessary

  
• Venipuncture on pediatric patients

  • Presents special challenges and requires the expertise and skill of an experienced phlebotomist
  • Removal of large quantities of blood at once or even small quantities on a regular basis, as is often the case when an infant or child is in intensive care, can lead to anemia (iatrogenic Anemia)
  • Removing more than 10% of an infant's blood volume at one time can lead to shock and cardiac arrest
• Pain Interventions


  1. Use of cold or vibration

  2. Topical anesthetics [EMLA, a eutectic (easily melted) mixture of local anesthetics] for newborns through adults

  3. Oral sucrose (the sucrose must be given to the infant 2 minutes before the procedure, and its pain-relieving benefits last for approximately 5 minutes)

  4. Pacifiers for infants and toddlers
• Choice of site for capillary sampling

  • Adult patients: Finger is usually the preferred site, sides of the heel are only used in pediatric and neonatal patients, ear lobes are sometimes used in mass screening or research studies
  • Pediatric and neonatal patients: Selection of a site is usually based on the age and weight of the patient, if the child is walking, the child's feet may have calluses that hinder adequate blood flow, specimens requiring a skin puncture are best obtained after ensuring that a baby is warm

  
• Conditions influencing the choice of heel or finger-prick

  • Age: Birth to about 6 months - Heel Prick, Over 6 months - Finger Prick
  • Weight: From 3-10 kg - Heel Prick, Greater than 10 kg - Finger Prick
  • Placement of lancet: Heel - Medial or lateral plantar surface, Finger - Side of the ball of the finger perpendicular to the lines of the fingerprint
  • Recommended finger: Second and third finger (i.e. middle and ring finger); avoid the thumb and index finger because of calluses, and avoid the little finger because the tissue is thin
• Order of Draw


  Hematology specimen collected first, followed by chemistry and blood bank specimens, this order is essential to minimize the effects of platelet clumping, the order used for skin punctures is the reverse of that used for venipuncture collection

  
• If more than two specimens are needed, venepuncture may provide more accurate laboratory results
• Proper Labeling of Tubes after Blood Collection

  
• Complications that can arise in capillary sampling

  • Collapse of veins if the tibial artery is lacerated from puncturing the medial aspect of the heel
  • Osteomyelitis of the heel bone (calcaneus)
  • Nerve damage if the fingers of neonates are punctured
  • Haematoma and loss of access to the venous branch used
  • Scarring
  • Localized or generalized necrosis (a long-term effect)
  • Skin breakdown from repeated use of adhesive strips (particularly in very young or very elderly patients) - this can be avoided if sufficient pressure is applied and the puncture site is observed after the procedure
• Practical Guide to consider in Capillary Collection

  1. Selection of site and lancet: Using the guidance to decide whether to use a finger or heel-prick, and decide on an appropriate size of lancet, DO NOT use a surgical blade to perform a skin puncture, DO NOT puncture the skin more than once with the same lancet, or use a single puncture site more than once, because this can lead to bacterial contamination and infection

  2. Take laboratory samples in the correct order to minimize erroneous test results: With skin punctures, collect the specimens in the order - hematology specimens, chemistry specimens, blood bank specimens

  3. Data entry or completion of requisitions: Record relevant information about the blood collection on the requisition and specimen label

  4. Comfort and reassurance: Show the child that you care either verbally or physically, a small amount of sucrose (0.012-0.12 g) is safe and effective as an analgesic for newborns undergoing venepuncture or capillary heel-pricks

  5. Unsuccessful attempts in pediatric patients: Adhere strictly to a limit on the number of times a pediatric patient may be stuck, if no satisfactory sample has been collected after two attempts, seek a second opinion to decide whether to make a further attempt, or cancel the tests
• Modified Allen Test


  1. Instruct the patient to make a tight fist, using your fingers, apply direct pressure on the radial and ulnar arteries to obstruct blood flow to the hand as the patient opens and closes his fist rapidly, examine the Palmar surface of the hand for an erythematous blush or pallor within 15 seconds

  2. A positive Allen's test is when a blush indicates ulnar patency, a negative Allen's test indicates occlusion of the ulnar artery, the radial artery should not be punctured

  
• Collection of drops of blood for testing can be obtained by puncturing or making an incision in the capillary bed in the dermal layer of the skin with a lancet, other sharp device, or laser

  
• Capillary specimen


  Mixture of arterial, venous, and capillary blood, along with interstitial fluid and intracellular fluid from the surrounding tissues
• Capillary blood contains a higher proportion of arterial blood than venous blood and therefore more closely resembles arterial blood in composition, especially if the area has been warmed
• Capillary puncture equipment


  • Lancets/incision devices
  • Microcollection containers
  • Microhematocrit tubes and sealants
• Types of microhematocrit tubes


  • Red or green band: Heparinated tube
  • Blue band: Non-additive tube
• Indications for capillary puncture in adults and older children


  • Available veins are fragile or must be saved for other procedures
  • Several unsuccessful venipunctures have been performed
  • The patient has thrombotic or clot-forming tendencies
  • The patient is apprehensive or has an intense fear of needles
  • There are no accessible veins
  • To obtain blood for POCT procedures such as glucose monitoring
• Reasons capillary puncture is the preferred method for infants and young children


  • Infants have a small blood volume
  • Large quantities removed rapidly can cause cardiac arrest
  • Obtaining blood by venipuncture is difficult and may damage veins and tissues
  • Puncturing deep veins can result in complications
  • An infant or child can be injured by the restraining method used for venipuncture
  • Capillary blood is the preferred specimen for some tests, such as newborn screening

  
• Differences between capillary and venous blood composition

  • Concentration of glucose is normally higher in capillary blood
  • Total protein, calcium, and potassium concentrations are lower in capillary blood
• Tests that cannot be collected by capillary puncture

  • Erythrocyte sedimentation rate methods
  • Coagulation studies that require plasma specimens
  • Blood cultures
  • Tests that require large volumes of serum or plasma
• Preferred site for capillary puncture in adults

  The finger
• Preferred sites for capillary puncture in pediatric and neonatal patients

  The sides of the heel
• Do not puncture any deeper than 2.0 mm when performing a heel puncture, as deeper punctures risk injuring the bone
• Order of draw for collecting multiple capillary specimens

  1. Hematology specimens first as they are most affected by the clotting process

  2. Serum specimens last as they are supposed to clot

  
• Capillary puncture blood is less desirable for blood gas analysis, primarily because of its partial arterial composition
• Order of draw for collecting multiple specimens by capillary puncture


  1. Hematology specimens collected first

  2. Serum specimens collected last

  
• Capillary blood gases (CBGs)


  Less desirable for blood gas analysis due to partial arterial composition and exposure to air during collection
• Collecting capillary blood gas specimens

  1. Warm site for 5-10 minutes to increase blood flow and arterialize specimen

  2. Proper collection technique to minimize air exposure
• CLSI order of draw for capillary specimens


  • Blood gas specimens (CBGs)
  • EDTA specimens
  • Other additive specimens
  • Serum specimens

  
• Neonatal bilirubin


  • Overproduction or impaired excretion can cause jaundice and brain damage
  • Bilirubin breaks down in light, so specimens must be protected from light
• Collecting neonatal bilirubin specimens


  1. Collect by heel puncture

  2. Collect quickly to minimize light exposure

  3. Use amber-colored micro collection containers to protect from light
• UV light must be turned off when collecting bilirubin specimen to prevent breakdown
• Newborn/neonatal screening


  • Performed on blood spots collected by heel puncture on filter paper
  • Can detect up to 30 different disorders
• Disorders tested in newborn screening

  • Phenylketonuria (PKU)
  • Hypothyroidism
  • Galactosemia
• Procedure for collecting newborn screening blood spots

  1. Aseptic technique

  2. Wipe away first blood drop

  3. Apply large drop of free-flowing blood to center of circle on filter paper

  4. Do not allow paper to touch heel

  5. Fill all circles completely on one side only

  
• Blood film/smear preparation


  • Required to perform manual differential blood cell count
  • Smears should be made within 1 hour of EDTA collection to avoid cell distortion

  
• Procedure for making blood smears


  1. Collect smears first before other specimens to avoid platelet clumping

  2. Skin puncture preferred for some tests like leukocyte alkaline phosphatase