Which tube follows the serum tube in the order of draw?

The serum tube is typically collected first in the order of draw because it allows for the serum to be separated from the cells without the interference of additives that could affect the sample. Following the collection of serum tubes, the next appropriate tube in the order of draw is the heparin tube, which is used for plasma testing and contains anticoagulants that prevent blood from clotting.

Heparin tubes are advantageous for tests that require plasma since they do not require the sample to be allowed to clot like serum. By drawing the heparin tube after the serum tube, you ensure that the results from both types of tubes are reliable and accurate, as the heparin acts differently than serum-separating additives.

In contrast, glycolytic inhibitors, EDTA, and blood culture tubes require different handling and can introduce preservatives or anticoagulants that may skew results if drawn before the serum tube. This careful sequencing is fundamental in phlebotomy practices to ensure the integrity of laboratory testing and avoid contamination.