How can a tourniquet effect the result to a blood test?

Venous blood sampling is usually performed using a tourniquet to help locate and define peripheral veins to achieve successful and safe venipuncture. Despite widespread usage of tourniquets for venipuncture by medical and laboratory staff, very few are aware of the effects of tourniquet application on laboratory parameters. In addition, definitive guidelines regarding when and how to use a tourniquet for blood sampling are lacking.

It can cause the blood to pool and negatively affect any results including:

cholesterol levels

glucose

liver

hemogolbin

to name a few

Also it can be affected by posture i.e. if sitting for 30 minutes before or lying down.