Why does no blood come when you have a blood test?

Answer 1

This could be for a number of reasons. The tube that was placed on the needle holder after the venipuncture, may have been void of vacuum. The needle may have gone completely through the vein to the other side. The vein may have just been missed entirely, or the bevel of the needle was resting against the inner wall of the vein.

Answer 2

there are many reasons for this. it can be the tech missed the vain do to the vain moving or rolling away for the needle. a valve in the vain closing perventing blood flow; your vains have doors in them called valve and when the blood flows in the wrong direction the valves will close. it can be that the needle is not in the vain all of the way... letting the blood flow under the skin making a bruise insead of the blood going in the needle to the tube. it can also be that the patient is dehydrated. when a patient comes into the lab dehydrated it take the techs a longer time to find a good vain to use. once the tech stick the vain the flow will be very slow.. that means the needle will have to stay in longer to get the peroper amount of blood to complete the tests.

 

as a tech if we get a patient that has a slow flow or no flow the best thing to do is restick the patient. when a patients flow starts to slow down that means the blood is starting to clot up or the valves are closing. if that clot gets into your EDTA tubes the specimen will be inadequate for testing and the patient will have to be re-drawn.

 

a note for patients: the more hydrated you are the better. when you come into lab hydrated the techs find the vains quickly and your blood flow is fast....meaning the needle does not stay in for a long time. the best way to hydrate yourself is to drink plain water. even if your doctor whats you to come in for fasting labs plain water will not effect the results.