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Types of Blood Collection Tubes and Their Significance

A blood collection tube is a sterile glass or plastic test tube with a coloured rubber or plastic top. This top creates a vacuity inside the tube, allowing a predefined volume of a blood sample to be drawn. Vacutainer tubes may have anticoagulating reagents that help in stabilising and preserving the sample prior to processing. Tubes come with a safety-engineered stopper, a choice of labelling and draw volume options. The colour of the cap indicates the additives or anticoagulants in the vial.

Principle of blood vials

The inner end of the Vacutainer needle has a thin rubber coating that prevents blood from spilling out. This is in case if the Vacutainer tubes are changed during a multi-draw of a blood sample for a package or multiple investigations for different departments at a pathology lab. The outer end is placed into the vein. The coated end of the needle is within the clear plastic needle holder when it is screwed in.

When a tube is inserted into the holder, the rubber cap is pierced by the inner needle. The blood is drawn through the needle and into the tube by the vacuum. After removing the filled tube, another can be inserted and filled in the same technique. The amount of air pumped out of the tube determines how much blood will flow into it until it stops.

A colour-coded plastic or rubber cap is placed at the top of each tube. Tubes often contain compounds that mix with the blood as it is collected, and the colour of the plastic cap on each tube indicates which additives or types of anticoagulants are present.

When the needle punctures the cap on a blood collection tube, the vacuum is released over time, and blood is not pulled into the tube.

Various vials and anticoagulants

Additional agents that preserve blood for processing may be present in vacutainer tubes. When using the wrong tube, the blood sample may not be usable for the specified reason and if used the values or results of the sample will be compromised. Thin-film coatings deposited with an ultrasonic nozzle are commonly used as additives.

Anticoagulants such as (EDTA, sodium citrate, and heparin) or a gel with a density between blood cells and blood plasma are examples of additives. Furthermore, some tubes contain chemicals that help maintain certain blood components or molecules, such as glucose. The components of a tube are divided by density when centrifuged. The blood cells sink to the bottom and plasma or serum accumulate at the top as supernatant. After centrifugation, tubes containing gel can be readily handled and carried without the blood cells.

Order of draw

The order in which tubes should be filled is referred to as the order of draw. This order is necessary since the needle that pierces the tubes has the potential to transmit additives from one tube to the next. The sequence is standardised to ensure that any additive cross-contamination does not occur and alter laboratory results.


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 Yash Batra

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