Collection of blood

INTRODUCTION 

Blood is one of the most common specimens used in laboratory determinations. 

Venous blood is preferred for most hematological examinations. 

Peripheral samples (capillary blood) can be used satisfactorily for many purposes if a free flow 

of blood is obtained, but this procedure should be avoided in patients who may be possible carriers of transmissible diseases. 

 Capillary blood is used commonly for hemoglobin estimation, cell counts, blood grouping, 

bleeding and clotting time determination, and other investigations that use less blood, whereas 

venous blood is preferred for a comprehensive hematological investigation.

What are Arteries?

Arteries are blood vessels that carry blood from the heart to the entire body. The blood is ‘mostly’ 

oxygenated in arteries. Arteries are also responsible for carrying nutrients to the cells.

Two exceptions where arteries carry deoxygenated blood.

i. Pulmonary artery where it carries blood from the heart to lungs and 

ii. second is the Umbilical artery which carries the blood from fetus to the placenta. 

What are Veins?

Veins are blood vessels that carry blood from the body to the heart. And again, it ‘mostly’ carries 

deoxygenated blood. The pulmonary and umbilical veins carry oxygenated blood to the heart. The 

veins have valves present in them. These valves prevent backflow (Flow in the reverse direction). 

Veins are also less muscular in comparison to arteries.

METHODS OF COLLECTION 

For physiology practicals, blood is often collected by pricking the tip of the finger. Therefore, 

collection of peripheral blood by finger puncture method is described clearly. 

Principle 

 There are two general sources of blood for clinical laboratory tests: peripheral (capillary) 

blood and venous blood. For small quantities of blood for hematologic investigations, the 

specimen is obtained from the capillary bed by puncturing the skin. The tip of the finger is the 

most common site for puncture. 

For larger quantities of blood, a puncture is made directly into a vein (phlebotomy) using a 

sterile syringe-and-needle collection system.

COLLECTION OF CAPILLARY (Peripheral) BLOOD

Capillary blood is often used for bedside investigations. But this blood is likely to give erroneous

results if not collected properly; therefore, it should only be used when it is not possible to obtain venous blood.

Free flow of blood is essential and only the very gentlest squeezing is permissible. Ideally, large

drops of blood should exude slowly but spontaneously.

Capillary blood sampling, which refers to sampling blood from a puncture on the finger, heel or an

earlobe, is increasingly common in medicine.

Capillary blood collection from Adults

Skin puncture blood sampling is also recommended for adult patients with

Severe burns,those who are obese or older or anxious about sampling,

Advantages

Capillary blood sampling has several advantages over venous blood sampling:

• it is less invasive,
• it requires smaller amounts of blood volume and
•  it can be performed quickly and easily.

Disadvantages

If carried out incorrectly, capillary blood sampling can causeinaccurate test results, pain and tissue damage.

COLLECTION OF BLOOD FROM VEINS (VENOUS BLOOD)

The process followed to draw blood is called Phlebotomy.

For blood sampling, blood is taken from veins and not arteries because:

 Veins are close to the surface of the skin. This makes the process easier by avoiding a

deep needle plunge just to draw a bit of blood. Arteries, on the other hand, are a tad bit

deeper.

PROCEDURE

1. The first step is to identify the vein. The most common vein for adults is the median cubitalvein.
2.  It’s a large vessel which makes drawing blood easier. It also gives excellent results if theblood is drawn properly.
3. The next step is to actually draw the blood.
4.  We begin by hyperextending the arm of the patient and putting the tourniquet around 3-4inches from the site. Tell the patient to form a fist and keep it tight.
5. Next is to cleanse the site with alcohol swabs.
6. Now grab the lower arm which helps to anchor the vein and stop it from rolling. Then insertthe needle at 15-30 degrees into the vein.
7. If done correctly, you can see blood in the catheter! Use the right tubes to remove the appropriate amount of blood.
8. Now remove the tourniquet and remove the needle.Then press down on the site with a gauze.
9. Label the tubes correctly and then provide it to the labs within time.

Venipuncture:

The blood that is collected, called venous blood, can then be used for a variety of purposes,

such as intravenous therapy, blood sampling, diagnosis and so on.