What should be done if blood does not flow into the collection tube?

Adjusting the angle of the needle is an appropriate action when blood does not flow into the collection tube. This is typically necessary because the initial angle may not be optimal for accessing the vein. Changing the angle can help the needle to better position itself within the lumen of the vein, facilitating blood flow into the tube.

When blood flow is not initiated, it's essential to investigate and correct the situation without creating unnecessary trauma or discomfort. A slight adjustment may help to redirect the needle's tip so that it can better engage with the vein, allowing for successful blood collection.

Other actions, such as applying pressure or pulling the needle out immediately, may lead to complications or further difficulties in obtaining the sample. Inserting a second needle at another angle could potentially cause more pain and complicate the procedure without first ensuring that the initial needle position is adjusted appropriately.