What can happen if the tourniquet is left on for too long during blood collection?

Leaving a tourniquet on for an extended period during blood collection can result in hemoconcentration, which refers to an increase in the concentration of blood components, such as cells and proteins, in the blood. This occurs because the tourniquet restricts venous return while arterial flow continues, causing the blood in the veins to become more concentrated. As a result, this can lead to inaccurate test results, as the elevated levels of certain analytes may not reflect the true values in the patient's circulatory system.

Hemoconcentration can significantly affect laboratory tests, particularly those measuring electrolytes, protein levels, and various cellular components. For example, if a blood sample drawn after an extended tourniquet application is tested for potassium levels, the concentration may appear artificially high, leading to potential misdiagnosis or inappropriate treatment decisions. Therefore, it is crucial to apply the tourniquet only for the minimal time necessary to facilitate a successful draw.