When collecting a blood sample from a central venous access device (CAD), the nurse should collect a small amount of blood in the discard tube. The exact amount will vary depending on the specific type of CVAD and the blood collection procedure being used.
In general, the nurse should collect enough blood in the discard tube to ensure that the sample is of sufficient volume and quality for testing. This may require collecting anywhere from 0.5 to 1.0 mL of blood in the discard tube.
It is important to note that the blood collected in the discard tube should not be used for testing. Instead, it should be discarded according to the hospital's procedures for handling biological waste. This is because the blood collected in the discard tube may be contaminated or compromised in some way, and therefore may not produce accurate or reliable test results.