Capillary Puncture: Medical Lab Science

• Lecture 7 focuses on Capillary Puncture, a key principle in Medical Laboratory Science.
• The lecturer is Ms. Khelly Mae B. Villarin, RMT.

Capillary Puncture

• Also known as dermal or skin puncture.
• Collection involves puncturing the capillary bed in the dermal layer with a lancet or similar device to obtain blood drops for testing.
• Yields only drops of blood, suitable for tests requiring small amounts. Not for tests requiring large amounts.
• Method of choice for blood collection from infants and children under 2 years old.
• Can be performed on adults.
• Composition is a mix of capillary, arterial, venous blood, interstitial fluid, and intracellular fluid. It closely resembles arterial blood because of arterial pressure.

Indications in Children

• Venipuncture is often unsuitable, reasons include:
• Superficial veins difficult to locate.
• Veins may need to be reserved for IV therapy.

Introduction

• Venipuncture is collecting blood from veins.
• Arterial puncture is collecting blood from arteries.
• Capillary puncture is collecting blood from capillaries or the capillary bed.

Indications

• Use of deep veins can be dangerous and may cause complications, such as:
  • Cardiac Arrest
  • Venous Thrombosis
  • Hemorrhage
  • Damage to Surrounding Tissue and Organs
  • Infection
  • Reflex Arteriospasm leading to Gangrene
• Drawing excessive amounts of blood from premature and small infants can rapidly cause iatrogenic anemia (anemia caused by frequent blood extractions).
  • Blood extraction should be limited to:
  • 1-5% of total blood volume within 24 hours
  • 10% of total blood volume within 8 weeks.
• Certain tests require capillary blood, such as blood glucose, microhematocrit
• Injury may occur by restraining a child for venipuncture.
• Not advisable if the patient is burned or scarred due to infection risk, decreased circulation, and difficulty in palpating veins.
• Preferred for patients receiving chemotherapy who require frequent tests and whose veins must be reserved for therapy.
• Used for patients who are likely to be thrombotic or have clot forming tendencies.
• Suitable for geriatric patients or patients with very fragile veins.
• Use when veins are inaccessible or the patient is obese or apprehensive about needles.

Home Glucose Monitoring or POCT

• Point of care testing, performed at the patient's bedside.
• Glucose testing is a common example.

Test Exemptions

• Suitable for children younger than 2 years old but limited by the small amount of blood it yields.
• Cannot be used for tests requiring large blood quantities.
• Examples of test exemptions:
  • Erythrocyte sedimentation rate (ESR): measures how quickly RBCs settle
  • Coagulation studies - Blood cultures: requires tests that need a large amount of blood

Equipment

• Lancet or Incision Devices: sterile, disposable sharp instrument.
• Selection of device depends on:
  • Age of patient.
  • Collection Site: finger or heel.
  • Volume of specimen required.
  • Puncture depth needed.
• Incision Depth (According to CLSI)
  • Should NOT exceed 2 mm to avoid hitting bone/causing conditions like as Osteomyelitis and Osteochondritis.
  • Target the dermal-subcutaneous junction (vascular area).
  • Newborns: 0.35-1.6 mm below the skin
  • Adults: up to 3 mm below the skin
• Incision Width (According to CLSI)
  • Should NOT exceed 2.5 mm to avoid injuries/bleeding
• Incision width is more important than incision length.
• Types of Finger-Puncture Lancets:
  • Feather Lancet: Manual control, conventional design.
  • BD Microtainer Contact-Activated Lancet: Release mechanism activated on the skin.
  • Tenderlett Incision Device: Color-coded for depth and gauge.
  • Greiner Bio-One Lancelot Safety Lancet
  • Unistik 3 Safety Lancet
  • Touch Activated Phlebotomy (TAP): Automated with vacuum and reservoir.
• Types of Heel-Puncture Lancets:
  • Tenderfoot Heel Incision Device
  • Unistik Tiny Touch
  • Quikheel Lancet

Microcollection Containers or Microtubes

• Serves as the counterpart to the evacuated tube.
• BD Microtainer tubes are designed to collect the minimal amounts of blood from capillary puncture
• Available with different anticoagulants and additives, including separator gel.
• Color-coded for anticoagulants.
• Has marks for minimum (250 μL) & maximum (500 μL) fill levels.
• Available from different manufacturer that make different tubes
• MiniCollect
  • Has a capillary tube and funnel to facilitate collection

Microhematocrit Tubes and Sealants

• Commonly called "Capillary Tubes."
• Narrow-bore, plastic or plastic-clad glass tubes that fill by capillary action.
• Typically hold 50-75 µL of blood.
• Variants:
  • Non-additive: blue top tube
  • Heparinized: green and red top tube
• Sealants:
  • Plastic
  • Clay
  • Wax-type

Warming Devices

• To improve blood flow to the area
• Achieve warming by:
  • Warm Washcloths/Towels
  • Commercial Heel Warmer like a packet contains sodium thiosulfate & glycerin. Apply for 3-5 min, don't increase more than 10 min.

Other Equipment

• Microscope Slides
• Alcohol Pads
• Gauze Pads
• Bandages
• Approved Sharps Container
• Capillary Blood Gas (CBG) Equipment

Collection Process

• Review and Accession Test Request
• Match needed equipment with tests ordered and note collection method on requisition form to help physician in the correct interpretation of results
• Approach, Identify and Prepare the Patient
  • Identification through:verbal identification (2 unique patient identifiers), ID band, requisition form
• To approach and prepare the patient:
  • Present a friendly/confident appearance
  • Do NOT say the procedure will not hurt
  • Explain the necessity of remaining very still -Diet restrictions & latex sensitivity
• Sanitize Hands and Put on Gloves: done within the view of the patient
• Position the Patient -Finger Puncture: Seated or lying down (Non-dominant hand on a firm surface and Palm up)
• Select the Puncture Site -Heel Puncture: Infant in a supine position -Primary Danger: accidental contact with the bone -Based Patient's age and size

Areas to Avoid

• Calluses
• Scared
• Bruised
• Edematous
• Cold or Cyanotic
• Infected
• Previous Puncture Site

On the Same Side of Mastectomy

• Possibility of the patient to develop lymphedema so prone to infection.
• Table 4: difference between finger and heel puncture sites to differentiate on what acceptable sites to use

Warm the Site, if Applicable

• Optional, use if a commercial heel warmer, washcloth or towel, with a maximum temperature: of 42°C to increase blood flow.
• Advantages: Makes specimen easier and reduces the tendency to compress or squeeze the site.
• Primarily required for:patients with very cold fingers, Heel punctures, Collection of CBGs (capillary blood gasses)

Clean and Air-Dry Site

• To prevent contamination and the CLSI-recommended antiseptic 70% isopropanol
• Allow to air-dry: Allows more antiseptic the function, Avoids the specimen with alcohol,Allows for a rounded blood drop
• Prepare Equipment - Select puncture devices and keep equipment within reach.

Perform the Puncture

• Ensure well-supported and held firmly
• Position the puncture device with the blade across (not along) the fingerprints and use pressure to keep it in place.
• Puncture and hold the release for a moment then remove from skin and place in sharps.
• Fill and Mix Tubes/Containers
  • Wipes away first drop and do NOT "milk" the site.
• Order of Draw
  • Capillary Blood Gas (CBG)
  • Blood Smear
  • EDTA Tube
  • Other Anticoagulated Tubes
  • Serum or Non-additive Tubes
• Check the Site and Apply Bandage
  • Confirm bleeding stopped (notify if more than 5 minutes)
  • Do not apply bandage except in: children under 2 years old, older adult patients & Newborns
• Dispose Used & Contaminated Materials properly
• Transport the Specimen Promptly

Special Procedures

• Capillary Blood Gas (CBG)
• Evaluation of oxygen and carbon dioxide blood levels
• Less desirable than ABG due: composition, air exposure
• Done in infants and young children with a Heparin container.

Blood Smear

• Done by placing a drop of blood then spreading it on a microscope slide.
• Purpose: for microscopic examination of blood cells
• Prepared from blood collection via:Venipuncture AND Dermal Puncture.
• About 2 minutes to finish the procedure.
• Characteristics of A Good Smear
  • Smooth film, Ideally covers slide,finger-shaped film, smooth transition
• Malarial Smear

Neonatal Bilirubin Collection

• A yellowish made during the breakdown of red blood cells.
• Hemolytic disease of newborn (HDN) only happens in second or further pregnancies.
• UV lights must be turned off
• Specimen Collection for the most part is a heel puncture.

Newborn Screening

• Mandated testing to prevent the death of a newborn by certain conditions.
• Blood Spot Collection needs to be taken with certain precautions like not getting anything touching the circles.