The Three General Methods of Blood Collection

Blood collection is a vital procedure in blood testing. Proper blood collection is required to ensure the reliability of results. The general methods for blood collection are (note that this is only a reference guide – you should only attempt this if you are a professional):

1. Venipuncture – It is the collection of blood from the veins through the use of a needle and a syringe. In this procedure, the most common site of venipuncture is the antecubital fossa where the cephalic, basilic and mid-cubital veins are found. This procedure is required when large amounts of blood is needed for testing like in glucose, cholesterol, uric acid, creatinine, alkaline phosphatase test, and many blood chemistry determinations.

Materials needed

Gauge 20-22 needle, syringe, tourniquet, wet and dry cotton, 70 % isopropyl alcohol, vacutainer tubes or test tubes.

Precautions:

1.1. Remove the tourniquet first before the needle. Patients who have blood dyscrasia may bleed to death.

1.2. Avoid prolonged application of the tourniquet because it will cause venous stasis which will adversely affect the results.

1.3. Do not jerk the needle out of the vein because this may injure the vein and will cause discomfort in the patient.

1.4. Do not puncture the vein through and through because this will cause hematoma which is a bluish discoloration of the skin.

1.5. Allow the patient to rest for at least 10 minutes to ensure that he does not feel faint or that bleeding has stopped.

1.6. Sterilize before puncturing to ensure that the procedure is aspetic.

2. Capillary puncture – also known as fingerstick or finger puncture, is used when smaller volumes of blood is needed, like when performing Complete Blood Counts (CBC), peripheral blood smears and malarial smears. This method is useful for pediatric, obese and elderly patients where veins are small and cannot be palpated. It may also make use of the earlobe and big toe as puncture sites.

Materials needed

Lancet, capillettes, wet and dry cotton, 70 % isopropyl alcohol

Precautions

2.1. Puncture only the specified area as it may traumatize unintended sites like the bones.

2.2. Discard the first drop as this is made up of tissue fluid.

2.3. Sterilize first before puncturing.

3. Arterial Puncture – is the collection of blood from the arteries. This is oxygenated blood, while venous blood is non-oxygenated blood. This is usually used in Blood Gas Analysis (BGA) where the pH of blood, bicarbonate (HCO3), carbonic acid (H2CO3) and total carbon dioxide (TCO2) are determined

Materials needed

Luer lock syringe, vacutainer tubes, wet and dry cottons, 70% isopropyl alcohol

Precautions

3.1. Press the site of puncture for more than 15-30 minutes because the pressure of blood in the arteries is stronger than that in the veins.

3.2. Sterilize properly before puncturing.

3.3. Observe anaerobic collection as most samples are for blood gas testing.

These are the most common methods of blood collection. Each is utilized according to the needs of the patient.