Blood Collection via Capillary Puncture Technique 1

Blood Collection via Capillary Puncture Technique 1

Fingerstick

This technique is useful for adults or children when only small amounts of blood are required.

Normally the most desirable site for obtaining a venous blood sample for laboratory testing is from the veins of the antecubital fossa area. However, a capillary puncture may be used when only small amounts of blood are needed, and when venipuncture would be too invasive or not possible because:

the patient has poor veins not suitable for a venipuncture

the patient has only one good vein that must be saved for another procedure

the patient is extremely apprehensive about the venipuncture procedure

When obtaining a sample from the fingertip and especially a series of samples it should be from

the non-dominant hand with the arm in the anatomical position and the hand below the heart.

In general, capillary punctures may be done on earlobes, fingertips, heels, or toes, however, earlobes, heels, and toes are not a site of choice, especially in adults. Earlobes, for example do not have that many capillaries and because heels and toes of adults tend to be extremely calloused and tough, these areas are almost exclusively used with neonates and younger infants.

There also seems to be some difference in the cell concentrations between capillary blood taken from the earlobe and venous blood. The site of choice in children as well as adults is the distal lateral aspect of the fingertip; usually the second or third finger.

The middle or ring finger is best used for this sort of blood collection.

If the patient's hands are cold, they may be warmed by holding them under warm running water

or by briskly rubbing them. You can invite the patient to step to the lavatory and wash the hands

with warm soapy water. This will not only cleanse and soften the skin but at the same time

effectively increase the blood flow to the fingers.

Massage the finger from hand to tip 5-6 times to increase the blood flow. This maneuver can be

best described as gently milking the finger -- not squeezing it! However, be careful not to over-do it

as it may cause erroneous results due to concentration of tissue fluids.

Cleanse the selected fingertip with 70% isopropyl alcohol. Wipe dry with a clean, dry piece of

gauze or cotton. Before piercing be sure that the finger is thoroughly dry. If the puncture site is

still moist the blood will not well up but begin to run. What you want is a well rounded drop of blood

sitting on the finger tip.

If you are using a lancet, remove the lancet from its container and grasp the lancet between

the thumb and forefinger. If you are using a finger puncture device, you will need to refer

to the instructions for the device you are using.

If using a finger, grasp the patient's finger firmly between the fingers and thumb of your other

hand. If using an earlobe, support it from behind with your fingers of the opposite hand and pierce

the fleshy outer rim of the earlobe with a lancet.

With a quick stabbing wrist motion -- down and right back up -- make a puncture lateral to the ball

of the finger. Using this area avoids the nerves of the fingertip and thus avoids unnecessary pain. The

cut should be perpendicular to the lines in the fingerprint so that the blood will form a drop.

Punctures made parallel to the fingerprint lines will allow blood to run down the finger.

Using the hands supporting the finger, squeeze it lightly to stimulate the flow of blood.

"Milking" the finger from proximal toward the distal end will also be effective in getting

a good blood flow. Be careful not to cause erroneous results due to introduction of

tissue fluids. The cut should be deep enough so that hard pressure is not required.

If gentle pressure is not enough to start blood flow, make another puncture starting at step #4.

Using a piece of dry, 2x2 clean cotton gauze square or similar pad, wipe off the first drop of blood, as this drop may be contaminated with tissue fluid and this may interfere with the test.

Still holding the finger lightly, fill a (heparinized) capillary pipette or other collecting device. The

capillary pipette should be held in an almost horizontal position with the tip touching the

drop of blood. The tube should not be allowed to touch the finger. Should more blood

be needed, a small test tube or commercial micro tube may be held beneath the finger and

blood dropped into it.

1. If the capillary tube is open at both ends

(a) Use your gloved finger to cover the top end opening

(b) hold the capillary tube horizontally and touch the open end to the drop of blood

(d) make sure the blood rises to the top line; there should be no air bubbles

2. If the capillary tube is plastic and closed at one end

(a) squeeze the tube or bulb, and hold the tube horizontally while

touching the open end to the drop of blood

(b) gently release pressure on the tube or bulb to draw up the blood

When sufficient blood has been obtained, place a clean, dry gauze pad or cotton ball over

the site and have the patient press with the thumb on the same hand until bleeding has stopped.

Discard used capillary tubes and lancets in a ‘sharps’ bin and drop contaminated swabs and

tissues and all non-sharp materials into a biohazard bag.