Venous blood vs Capillary blood sampling

According to the Franklin Institute, the adult vascular system could span out to 100,000 miles in length, and each blood vessel is equally important.

There are three types of blood in your body - arterial, venous and capillary.

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Arterial blood - is oxygenated blood and is pumped through the pulmonary vein, left heart chamber and arteries in your body.  

Venous blood - is deoxygenated blood and is pumped through the peripheral blood vessels. The blood goes through the venous system into the right heart chamber. Deoxygenated blood is pushed through the heart by the right ventricle into the lungs using the pulmonary artery which has two branches. The blood then passes through the lungs and gets oxygenated. Coming through the pulmonary veins, it returns to the left atrium.

Capillary blood - is not the same as venous blood or arterial blood. However, these types of blood samples usually yield quality results when doing blood tests.

Capillary blood samples are used in a finger-prick test. They are useful for dry blood spot testing, are easier to collect from pediatric patients, and the smaller volume collected is simpler to handle, especially in remote settings. Finger-prick tests can be easily done at home without special medical training. However, the sample collection time may take much longer than with a venous blood sample - up to 30 minutes - compared to an about 5-minute venous blood sample collection done by a trained medical professional.

Usually, capillary blood is collected in the following cases:

• When only a small sample is needed
• When veins are not accessible
• In newborns because taking large amounts of blood may cause anaemia or heart issues
• To reduce risks in patients with anticoagulant issues

Both venous and finger-prick blood samples are accurate ways of measuring your body’s key biomarkers. Usually, most blood analyses are conducted using samples taken from a vein, but now more and more finger-prick testing is gaining popularity. Rarely, complications may arise from a venipuncture, some of which may include:

• Haematoma at the blood draw site
• Nerve damage
• Hitting a bone

If you are planning to collect a large volume of blood, it would be wiser to do a venous blood draw.  Additionally, there are several issues that may arise from an at-home finger-prick test:

• Not collecting enough blood for a sample. If the sample is too small, then the laboratory might struggle with getting enough plasma for testing. We usually only provide the finger prick option for tests when we are confident it will provide an adequate sample and an accurate result.
• When patients squeeze their fingers to draw blood, they might cause the red blood cells to burst, and this can taint the surrounding sample due to excess haemoglobin. This may also happen if a person scrapes their finger on the edge of the test tube

These types of errors are less likely to arise with a venous sample taken by a trained phlebotomist.