Ear lobe - The ear lobe has been used for capillary blood sampling, but is no longer recommended. Studies have shown that the blood flow in the ear lobe is less than that in either the finger tip or the heel. The ear lobe can still be used if no other site is available. The information given here supplements that given in Chapter 2. Users of these guidelines should read Chapter 2 before reading the information given below. This chapter covers background information (Section 7.1), practical guidance (Section 7.2) and illustrations (Section 7.3) relevant to capillary sampling.
Capillary 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. However, because the procedure is commonly used in paediatric patients, Sections 7.1.1 and 7.1.2 focus particularly on paediatric capillary sampling.
7.1.1. Choice of site
Adult patients
The finger is usually the preferred site for capillary testing in an adult patient. The sides of the heel are only used in paediatric and neonatal patients. Ear lobes are sometimes used in mass screening or research studies.
Paediatric and neonatal patients
Selection of a site for capillary sampling in a paediatric patient 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. shows the conditions influencing the choice of heel or finger-prick.
Table 7.1
Conditions influencing the choice of heel or finger-prick.
Specimens requiring a skin puncture are best obtained after ensuring that a baby is warm, as discussed in Section 6.2.2.
7.1.2. Selecting the length of lancet
Adult patients
A lancet slightly shorter than the estimated depth needed should be used because the pressure compresses the skin; thus, the puncture depth will be slightly deeper than the lancet length. In one study of 52 subjects, pain increased with penetration depth, and thicker lancets were slightly more painful than thin ones (67). However, blood volumes increased with the lancet penetration and depth.
Lengths vary by manufacturer (from 0.85 mm for neonates up to 2.2 mm). In a finger-prick, the depth should not go beyond 2.4 mm, so a 2.2 mm lancet is the longest length typically used.
Paediatric and neonatal patients
In heel-pricks, the depth should not go beyond 2.4 mm. For premature neonates, a 0.85 mm lancet is available.
The distance for a 7 pound (3 kg) baby from outer skin surface to bone is:
medial and lateral heel – 3.32 mm;
posterior heel – 2.33 mm (this site should be avoided, to reduce the risk of hitting bone);
The recommended depth for a finger-prick is:
Too much compression should be avoided, because this may cause a deeper puncture than is needed to get good flow.
7.1.3. Order of draw
With skin punctures, the haematology specimen is collected first, followed by the chemistry and blood bank specimens. This order of drawing is essential to minimize the effects of platelet clumping. The order used for skin punctures is the reverse of that used for venepuncture collection. If more than two specimens are needed, venepuncture may provide more accurate laboratory results.
7.1.4. Complications
Complications that can arise in capillary sampling include:
collapse of veins if the tibial artery is lacerated from puncturing the medial aspect of the heel;
osteomyelitis of the heel bone (calcaneus) (68);
nerve damage if the fingers of neonates are punctured (69);
haematoma and loss of access to the venous branch used;
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.
7.2. Practical guidance on capillary sampling
7.2.1. Selection of site and lancet
Using the guidance given in Section 7.1, 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.
7.2.2. Procedure for capillary sampling
Adult patients
Prepare the skin
Apply alcohol to the entry site and allow to air dry (see Section 2.2.3).
Puncture the skin with one quick, continuous and deliberate stroke, to achieve a good flow of blood and to prevent the need to repeat the puncture.
Wipe away the first drop of blood because it may be contaminated with tissue fluid or debris (sloughing skin).
Avoid squeezing the finger or heel too tightly because this dilutes the specimen with tissue fluid (plasma) and increases the probability of haemolysis (60).
When the blood collection procedure is complete, apply firm pressure to the site to stop the bleeding.
Take laboratory samples in the correct order to minimize erroneous test results
Paediatric and neonatal patients
Immobilize the child
First immobilize the child by asking the parent to:
–sit on the phlebotomy chair with the child on the parent's lap;
–immobilize the child's lower extremities by positioning their legs around the child's in a cross-leg pattern;
–extend an arm across the child's chest, and secure the child's free arm by firmly tucking it under their own;
–grasp the child's elbow (i.e. the skin puncture arm), and hold it securely;
–use his or her other arm to firmly grasp the child's wrist, holding it palm down.
Prepare the skin
Prepare the skin as described above for adult patients.
DO NOT use povidone iodine for a capillary skin puncture in paediatric and neonatal patients; instead, use alcohol, as stated in the instructions for adults.
Puncture the skin
Puncture the skin as described above for adult patients.
If necessary, take the following steps to improve the ease of obtaining blood by finger-prick in paediatric and neonatal patients:
–ask the parent to rhythmically tighten and release the child's wrist, to ensure that there is sufficient flow of blood;
–keep the child warm by removing as few clothes as possible, swaddling an infant in a blanket, and having a mother or caregiver hold an infant, leaving only the extremity of the site of capillary sampling exposed.
Avoid excessive massaging or squeezing of fingers because this will cause haemolysis and impede blood flow (60).
Take laboratory samples in the order that prevent cross-contamination of sample tube additives
As described above for adult patients, collect the capillary haematology specimen first, followed by the chemistry and blood bank specimens.
Collect all equipment used in the procedure, being careful to remove all items from the patient's bed or cot; to avoid accidents, DO NOT leave anything behind.
Give follow-up care
There are two separate steps to patient follow-up care – data entry (i.e. completion of requisitions), and provision of comfort and reassurance.
Data entry or completion of requisitions
Record relevant information about the blood collection on the requisition and specimen label; such information may include:
–date of collection;
–patient name;
–patient identity number;
–unit location (nursery or hospital room number);
–test or tests requested;
–amount of blood collected (number of tubes);
–method of collection (venepuncture or skin puncture);
–phlebotomist's initials.
Comfort and reassurance
Show the child that you care either verbally or physically. A simple gesture is all it takes to leave the child on a positive note; for example, give verbal praise, a handshake, a fun sticker or a simple pat on the back.
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 (70).
Unsuccessful attempts in paediatric patients
Adhere strictly to a limit on the number of times a paediatric 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.
In what case would a capillary puncture be contraindicated?
Capillary collection should not be performed on adult patients if adequate veins are available and patient is willing to allow their use. Also, capillary collection should be avoided if patient is dehydrated, has edema, or presents with poor circulation to the extremities.
What are four contraindications to capillary puncture?
There are some instances where a dermal puncture is prohibited or not recommended..
Mastectomy patients. As a general rule, a dermal puncture, or a venipuncture, should not be performed on the side affected by a mastectomy. ... .
Edematous site. ... .
Dehydrated patient. ... .
Fingerstick on a newborn or young infant..
What are the areas that should be avoided with a capillary puncture?
The posterior heel and toe should be avoided as puncture sites because the distance between the skin surface and the bone in each case is only 2.33 or 2.19 mm, respectively, which means greater risk of bone damage (3, 13).
Which of the following conditions disqualifies a site for capillary puncture?
capillary puncture equiptment and procedures.
