How can a tourniquet effect the result to blood test?

Applying a tourniquet before drawing blood for a blood test can affect the results in several ways:

Hemoconcentration: When a tourniquet is applied, it compresses the vein, restricting the flow of blood back to the heart. This can cause the blood in the arm to become more concentrated, as fluid is forced out of the vessels and into the tissues. As a result, the concentration of analytes in the blood sample may be higher than it would be if the tourniquet was not used.

Hemolysis: Applying a tourniquet for an extended period can damage red blood cells, leading to hemolysis. Hemolysis releases hemoglobin into the plasma, which can interfere with certain blood tests, such as those measuring electrolytes or bilirubin.

Arterialization of venous blood: When a tourniquet is applied too tightly or for too long, it can obstruct the venous flow while allowing arterial blood to enter the vein from collateral vessels. This can result in the collection of arterial blood instead of venous blood, which can alter the test results. Arterial blood has different composition from venous blood.

Pain and discomfort: Applying a tourniquet can cause pain and discomfort to the patient. This can lead to anxiety and stress, which can affect the accuracy of certain blood tests, such as those measuring cortisol or other stress hormones.

To minimize these effects, the tourniquet should be applied only when necessary and released as soon as the blood sample is collected. Proper tourniquet techniques and appropriate training of healthcare professionals performing blood draws are essential to ensure the accuracy and reliability of blood test results.