Capilliary blood sampling

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Audience

This Guideline is applicable to all medical and nursing staff working in neonatal units in The West of Scotland.

Introduction

A capillary sample is a blood sample collected by pricking the skin. Capillaries are tiny blood vessels which are near the skin surface.

In the neonate it is generally performed by heel puncture/stick. This is a minimally invasive and easily accessible method of obtaining capillary blood samples for a variety of tests. Heel puncture/stick sampling can also help preserve venous access for future intravenous lines.

Capillary sampling can be used to take small volume specimens for monitoring:

  • Blood glucose levels
  • Blood gases
  • Full blood counts
  • Serum Bilirubin
  • Urea and electrolytes
  • Drug levels  
  • Newborn Bloodspot Screening Tests

Good technique is important to avoid the following problems

Sample Problems

  • Inadequate sample volume – requiring a repeat specimen
  • Clotted sample – giving false +ve for thrombocytopenia or requiring a repeat specimen
  • Sample from poorly perfused heel – overestimation of degree of acidosis and hypercarbia
  • Haemolysed specimen – giving abnormal parameters such as high K+ or no result

NB – Consideration should be given to repeating a specimen, possibly using a venous sample, if the result is out of keeping with the baby’s condition or previous results.

Morbidity for the baby    

  • Increased pain
  • Local trauma  
  • Infection
  • Damage to nerves, blood vessels and bones
  • Excessive blood loss
Preparation

Cluster Care

Prior to carrying out any procedure on a baby the practitioner must be familiar with the infant’s plan of care. In order to provide developmentally supportive care an effort should be made to cluster any blood samples required as well as trying to time the sampling with the baby’s cares as far a possible.

Check patient ID

Ensure positive identification of baby and that name bands, blood forms and bottles all correlate. Double check Chi number in case of twins to ensure right test, for right baby and labelled appropriately.

Consent

If required, consent should be sought from parents prior to the procedure being carried out e.g. Newborn bloodspot screening.

Ensure a Safe Environment.

Ensure the baby is appropriately positioned/contained/swaddled.

Analgesia

Whenever possible, involve the mother in the procedure, using skin to skin contact, breastfeeding or non-nutritive sucking. For some procedures oral sucrose may be used – see oral sucrose guideline.

Identifying an appropriate site

The shaded areas on the lateral aspects of the heel are the preferred sites as this avoids the main nerves.

The area should be examined for previous, recent, puncture sites and the chosen site rotated if frequent sampling is required.
Procedure

Requirements

  • Non-sterile gloves
  • Cotton wool or gauze
  • Capillary tube and/or blood bottles
  • Blood lancet for puncturing the skin – An automated incision device should be used
  • Clean disposable tray to hold equipment
  • Sharps disposal box 
  • Alcohol Wipe
  • Soft Paraffin – this may not be required for small specimens such as a simple blood gas analysis. It may prove useful for larger specimens.
    • For NICU / SCBU babies – each baby to have an individual tube
    • For OPD or PNW settings a small quantity may be squeezed onto the edge of the procedure tray before the procedure commences

Procedure for obtaining the sample

This is not a sterile procedure however a clinical hand wash should be performed or alcohol gel applied (See antisepsis guidelines) before donning gloves.

To obtain the blood sample:

  •  Give appropriate analgesia/consider parental involvement as above
  • Ensure baby is lying in a safe and secure position
  • Hold the baby's heel with the non-dominant hand
  • Hold the ankle with index and middle finger
  • Use other fingers to steady the baby’s leg
  • Partly encircle the baby’s heel with thumb
  • Clean the proposed puncture site with an alcohol wipe and allow to dry for 30 seconds
  • Gently compress the heel and hold the skin under tension
  • Puncture the skin in a steady and intentional manner
  • Relax tension and wipe away initial blood flow with cotton wool or gauze
  • Whilst maintaining grip hold the heel so that blood is allowed to hang
  • Gently but firmly compress the baby’s heel to form a large droplet of blood
  • Do not squeeze the heel
  • Allow the heel to hang below down to assist blood flow
  • Hold the capillary tube or blood bottle to the blood droplet and touch
  • Momentarily release pressure to collect subsequent blood then reapply pressure, allowing the blood to flow
  • Continue until sufficient blood has been obtained.
  • If blood flow stops, clean site of old blood allow time for capillary refill, reposition hand and reapply pressure. If blood does not flow choose another site and repeat procedure.

Completing the Procedure

Once the sample has been obtained:

  • Apply pressure to the site with gauze
  • Maintain pressure until bleeding has stopped
  • It is not essential to apply a plaster, and these are best avoided in the hospital setting. If there is minor oozing then a spot plaster or a gauze ball and hypoallergenic tape may be applied for a few minutes. These should be removed when oozing has ceased
  • The baby should be left comfortable.
  • Equipment should be disposed of according to Hospital Waste Policy.
  • The person performing the skin puncture should wash their hands.
  • The sample should be sent for analysis as soon as possible
References

Blumenfeld TA, Turi GK, Blanc WA (1979) Recommended site and depth of newborn heel skin punctures based on anatomical measurements and histopathology. Lancet 1 (8110): 230-3.

Mancini AJ (2004) Skin. Pediatrics 113 (4 Suppl): 1114-9.

McIntosh N, Van Veen L, Brameyer H (1993) The pain of heel prick and its measurement in preterm infants. Pain 52 (1): 71-4.

Royal College of Nursing (2005) Competencies: an education and training competency framework for capillary blood sampling and venepuncture in children and young people. London, RCN

Royal College of Nursing (2010) Restrictive physical intervention and therapeutic holding for children and young people. London, RCN

Wallymahmed M (2007) Capillary blood glucose monitoring. Nursing Standard 21,38: 35-38

Editorial Information

Last reviewed: 16 September 2019

Next review: 01 September 2019

Author(s): L. Raeside - ANNP RHC

Co-Author(s): Other Professionals Consulted: Dr J Simpson - Neonatal Consultant RHC; Dr L. Jackson - Neonatal Consultant RHC

Approved By: West of Scotland Neonatology Managed Clinical Network