Neonatal blood sampling protocol Capillary sampling by heel prick is the most frequently used method for blood sampling in the neonatal period. It may be used to obtain blood samples for a range of indications (see below.) The technique is simple and involves relatively small sample volumes but heel pricks have been shown to be more painful than venepuncture in neonates, so care should be taken to plan tests in order to minimise the number of occasions blood sampling is required. Capillary samples should only be done by appropriately trained staff.
Indications for obtaining blood by Heel-prick
- Blood gas analysis
- Cot-side blood glucose measurements
- Most biochemical investigations: need free flowing sample to avoid haemolysis
- Full blood count: need free flowing sample to avoid clots / platelet clumps
- Capillary blood samples are not suitable for blood cultures or coagulation studies – both of these require venepuncture.
- Tray with integral sharps container
- Alcohol skin swab for skin cleaning
- Petroleum jelly to apply to skin
- Safety flow lancet (guarded needle prevents over-deep penetration)
- Capillary tubing and/or sample bottles (depending on nature of samples required)
- Sterile gauze swab
- Disposable tray or kidney dish for capillary blood gas samples
Method for collection
- Ensure foot is warm and well perfused before attempting capillary sampling
- Put on apron and wash hands as per Trust guidelines with soap and water
- Clean the skin with an alcohol swab and allow to dry
- Using a safety flow lancet, apply lancet to the skin of the heel avoiding excessive direct pressure.
- Depress the button to prick the heel once within the area described below.
- Gently squeeze the foot and allow a droplet of blood to accumulate. Collect this either in a capillary tube or sample bottle. Repeat this – it should be possible to collect at least 0.5mL of blood by heel prick from a well-warmed foot.
- When sampling is complete, stop the bleeding by gentle pressure with cotton wool.
- When collecting capillary samples for blood gas analysis, expel any air bubbles as if even 1% of the sample volume is air this can affect the results
- Remove gloves and apron and decontaminate hands.
- Dispose of waste to Clinical Waste Sharps container
Acceptable sites for sampling
Heel lancing should be limited to the medial and lateral borders of the heel (please see diagram below.) In preterm infants, who undergo many repeated capillary blood samples during the course of their care, the close clustering of puncture sites may lead to significant trauma and tissue injury over time. Newer devices have been introduced for heel lancing that limit the depth of penetration of the blade (generally to a depth of 2.4mm), therefore reducing the risk of inadvertent injury to deep structures, including the calcaneum. Capillary blood sampling may generally be safely carried out over the whole of the heel pad, allowing repeated samples to be taken over a wider area and reducing the trauma to the heels overall.
Guidance on collection
Please see diagram below for the paediatric equivalents of the adult tubes required for certain investigations. Given the precious nature of paediatric specimens and the importance of effective, timely clinical management in the neonatal period it is doubly important that the correct sample types are collected and where the analyte in question is known to be labile (i.e. unstable) samples are to be brought to the laboratory directly and handed to qualified staff in person.
The following samples are labile and require special consideration: -
- Plasma/ CSF amino acids
- Urine amino acids/ Organic acids
- Very Long Chain Fatty acids
- Plasma/ CSF Lactate
- Insulin/ C-Peptide
For guidance on the biochemical workup required for assessment of suspected inborn errors please refer to Trust guidance or otherwise that of the Great Ormond Street External User guide, which also provides detailed information on specific sample requirements for a wide variety of esoteric (i.e. non-routine) investgations...