What can cause hemoconcentration during blood collection?

Hemoconcentration occurs when the concentration of blood components, such as cells and proteins, increases relative to the plasma. This can happen when the blood is pooled in a specific area, leading to a reduced volume of plasma. Prolonged tourniquet application is a primary cause of this phenomenon. When the tourniquet is left on for too long before the blood draw, it restricts venous blood flow while allowing arterial blood flow to continue. As a result, the plasma begins to seep into surrounding tissues and the blood sample drawn may reflect an artificially elevated concentration of cells and proteins.

In contrast, while incorrect needle size, using an expired tube, and excessive fluid intake before testing can lead to various issues during blood collection or testing, they do not directly lead to hemoconcentration. An incorrect needle size might affect the quality of the sample or cause difficulty in blood collection. An expired tube can compromise the integrity of the sample and give unreliable results. Excessive fluid intake before testing can actually dilute blood components rather than concentrating them. Therefore, the prolonged application of a tourniquet stands out as the correct answer when specifically considering factors that cause hemoconcentration during blood collection.