During which phase is a blood sample most likely to be contaminated?

The pre-analytical phase is crucial because it encompasses all activities that occur before the actual analysis of the blood sample. This phase includes patient preparation, specimen collection, handling, and transportation to the laboratory. It is particularly vulnerable to contamination due to various factors, such as improper skin antisepsis, use of contaminated equipment or supplies, or even environmental factors during handling.

During blood collection, for instance, if the skin is not adequately cleansed or if the collection device is not sterile, pathogens can easily enter the sample. Additionally, the way the sample is stored or transported can introduce contaminants, further compromising the integrity of the specimen before it even reaches the analytical phase.

In contrast, the other phases—post-analytical and analytical—primarily focus on the processing of already collected samples and the interpretation of results, respectively. While issues can occur during these phases, they generally do not relate to the initial contamination of the blood sample. Therefore, the highest risk for contamination lies squarely in the pre-analytical phase.