Dialysis Technician Practice Exam

When drawing a blood specimen from a double lumen catheter, what should be done first?

1. Discard the first 4-5 ml of blood

2. Apply pressure to the site

3. Use a syringe with a larger volume

4. Clamp the catheter before drawing

The correct answer is: Discard the first 4-5 ml of blood

When drawing a blood specimen from a double lumen catheter, discarding the first 4-5 ml of blood is crucial because it helps to eliminate any possible contamination from the catheter or the external environment. The initial blood that flows from the catheter may not accurately represent the patient's current blood values because it can contain residual saline or anticoagulants that were used to maintain catheter patency. By discarding this initial volume, you ensure that the specimen collected is more representative of the patient's actual blood composition, thus improving the accuracy and reliability of lab results. In any laboratory practice, the quality of the specimen is paramount. This step is commonly referred to as "waste volume" and is a standard practice to mitigate contamination risks and ensure that subsequent samples are as reliable as possible. This procedure aligns with best practices in phlebotomy and venipuncture, thereby maintaining the integrity of the specimen for analysis.