ASCP Histotechnician Certification Practice Exam 2025 – Your All-in-One Guide to Exam Success!

When an EDTA tube for a complete blood count (CBC) is left out overnight, the parameter most likely to be compromised is the white blood cell differential. This is primarily due to the fact that white blood cells are sensitive to ambient conditions and can undergo lysis or other changes over time if not properly handled. Specifically, the cellular morphology, which is crucial for accurate differentiation of the various types of white blood cells, can deteriorate, leading to inaccurate counts and classifications.

In contrast, while platelet counts, hemoglobin levels, and red blood cell counts may also be affected by prolonged exposure at room temperature, they are typically more stable than white blood cell differential counts. Platelets may clump together over time, which could minimally affect their count, but this is not as significant as the changes experienced by white blood cells. Hemoglobin and red blood cell counts can also remain relatively stable unless severe hemolysis occurs, which is less likely overnight in proper conditions. Therefore, the concern about accuracy is heightened with the white blood cell differential in this scenario.