During IV sampling, how long should the IV be turned off and how much first sample should be discarded?

• A. 2 minutes; 1-2 mL
• B. 2 minutes; 3-5 mL
• C. 5 minutes; 3-5 mL
• D. 5 minutes; 6-8 mL

Answer: (A)

When drawing blood through an IV line, the aim is to prevent IV fluids or medications from contaminating the sample. Turning the IV off for about 2 minutes gives the line a moment to clear residual IV solution and minimize backflow into the sampling syringe. Discarding a small amount, around 1–2 mL, removes the initial sample that could still be mixed with IV fluid, so the subsequent draw better reflects the patient’s true blood composition. Longer pauses or larger discard volumes don’t provide meaningful added benefit and can waste blood or delay testing. If IV therapy is essential for the patient, you might need an alternative venipuncture for certain tests, but for routine IV sampling, the described approach balances accuracy with practicality.