The order that blood is collected in collection tubes during a multiple tube draw or filled from a syringe must be done correctly otherwise there is an increased chance of contamination due to additive carryover, tissue thromboplastin, or microorganisms. The order of draw is a specific sequence of tube collection that should be used to minimize problems. The order of the draw may vary among institutions. A phlebotomist should always use the institutional protocol.
It can be difficult to remember which additives affect which tests. This is why the order of the draw is helpful. By following the specific order you can eliminate confusion and use a sequence of collection that will prevent the least amount of interference should any carryover happen. The best way to minimize the chances of carryover is to fill specimen tubes from the bottom up during collection. Also try and prevent the tube from coming into contact with the needle during the draw or when transferring blood into tubes from a syringe.
There are several types of contamination that can occur during a multiple tube draw or filled from a syringe.
Carryover/Cross Contamination- This type of contamination occurs from the transferring of additive from one tube to another tube. It can occur when blood in an additive tube touches the needle during evacuated tube system (ETS) blood collection. It can also occur when blood is transferred from a syringe into ETS tubes. If blood remains on or within the needle, it can be transferred from a syringe into ETS tubes.
Tissue Thromboplastin Contamination- This form of contamination can occur when tissue thromboplastin interferes with coagulation tests. This can happen when a needle picks up tissue thrombinoplastin during venipuncture and fills the first tube during ETS collection.
Microbial Contamination- Blood culture tubes are sterile and should be collected first to ensure that they maintain their sterility to prevent microbial contamination of the needle from the unsterile tubes that are used to collect other blood specimens. Special site-cleaning measures should be taken prior to collection to prevent specimen contamination by microoganisms that are found on the skin.