# Capillary Blood Sampling

## Overview

This module describes how to obtain a capillary blood sample by pricking the finger or foot.

## Indications

1. Glucose or haemoglobin testing
2. Bilirubin testing in babies
3. Rapid tests such as for HIV or COVID-19 antibodies

## Contraindications

1. Damaged or infected skin, or distorted anatomy at the site

## Patient information and consent

Always verify your patient’s identity and obtain informed consent before proceeding.

### How do I explain this procedure?

“I need to prick your finger (or your child’s heel) to get a drop of blood to test it.”

### What can my patient expect?

“You may feel a sharp prick, but it will only be painful for a moment. I’ll take a drop of blood for the test. The test results will be available within a few minutes.”

### What is my patient’s role?

“Fearing blood or needles is normal, but tell me if you have fainted from it. Keep as still as possible. Afterwards, press firmly on the area with cotton wool to prevent bleeding.”

## Preparation

### Documentation

1. Patient notes

### Equipment

1. Non-sterile gloves

2. Alcohol-based hand rub

3. Sharps container
   Sharps container

   If a sharps container is not within arm's length, use a kidney dish or other hard container to temporarily hold used sharps and to carry them to the sharps container for disposal.

4. Safety lancet
   Safety lancet

5. Alcohol swab (or cotton wool and saline if testing

   bilirubin
   bilirubin

   Alcohol can cause false results in bilirubin tests.

   )

6. Cotton wool ball

7. Measuring device and test strips as required

## Site & Positioning

In babies and infants under walking age, the sides of the heel are used. In children of walking age and adults, the middle or ring fingers are preferred. Fingers should be punctured on the sides of the fingertip, with the lancet perpendicular to the fingerprint.

Uncooperative children may need to be

restrained

restrained

The parent should sit with the child on their lap, with their legs crossed over the child’s legs. The parent should tuck the child’s arm under their own, using one hand to hold the free wrist and the other to hold the elbow extended.

.

## Procedure

​​Follow medical asepsis with non-sterile gloves.

1. Perform hand hygiene and don gloves.

2. Ensure that you know how your measurement device works; some require you to insert the test strip before applying blood to it.

3. Clean the site.

4. Hold the finger or heel steady, apply the lancet to the site, and trigger it.

5. Wipe away the

   first drop of blood
   first drop of blood

   The first drop may give inaccurate results.

   with cotton wool.

6. Squeeze blood out of the puncture by applying gentle pressure up the finger or heel.

7. Collect the blood sample using the test strip, pipette, or other sampling device.

8. Apply pressure with cotton wool; ask the patient to take over while you perform the test and document the results.

9. Dispose of medical waste safely.

10. Record the completion of the procedure in patient notes.

## Troubleshooting

I don't have a lancet available.

Gently but swiftly prick skin with a needle, preferably a small (brown) needle.

I didn't obtain bleeding with the prick.

Bleeding may be affected by skin being calloused and thick, or if the patient has cold extremities or poor circulation. Avoid

aggressive squeezing

aggressive squeezing

Aggressive squeezing may cause inaccurate results by mixing blood with fluid from the tissues; if unsuccessful at another site, apply pressure to the base of the finger and gently "milk" toward puncture site.

of the site. Try using a longer lancet or a needle and puncture a different finger.

## Risks

1. Haematoma or scarring at the site

2. Skin breakdown from repeated sampling and use of adhesive plasters

3. Puncturing a

   bone
   bone

   This can happen if the centre of the heel or the little finger are used.

   with subsequent infection (osteomyelitis)

4. Injuring a

   nerve
   nerve

   Mostly happens when neonates' fingers are erroneously used.

## References

1. WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy. Geneva: World Health Organization; 2010. Available from: https://www.ncbi.nlm.nih.gov/books/NBK138661/
2. Jońca M, Krótki F, Tomasik P. The effect of disinfecting procedure on the glucose concentration using a personal glucose meter. Primary Care Diabetes. 2021;15(5):848-852.