If the 10 mL flush is not discarded when drawing blood from a peripherally inserted central catheter (PICC) line, will it dilute the hemoglobin specimen?

Blood Draw from PICC Lines: Waste Volume Requirements

Yes, failing to discard 10 mL from a PICC line before drawing blood will dilute the hemoglobin specimen and compromise accuracy. The waste volume is essential to clear residual flush solution (saline or heparin) from the catheter dead space that would otherwise contaminate your sample.

Why the 10 mL Discard Matters

The 10 mL waste volume for adult central venous catheters, including PICCs, is specifically designed to ensure sample accuracy by removing all residual flush solution from the catheter lumen. 1 This recommendation comes from established guidelines for blood sampling from venous catheters.

Mechanism of Dilution

• Residual flush solution in the catheter dead space will mix with blood during sampling, artificially lowering hemoglobin values 1
• The dead space volume varies by catheter type and length, but the 10 mL discard provides a safety margin to ensure complete clearance 1
• Even small amounts of saline contamination can significantly alter laboratory values 2

Evidence-Based Waste Volume Requirements

Standard Practice for Central Venous Catheters

For adult patients with central venous catheters (including PICCs), withdraw 10 mL of blood as waste before collecting the diagnostic sample. 1 This volume ensures that:

• All heparin and saline are removed from the catheter lumen 1
• The subsequent blood sample represents true patient values without dilution 1
• An additional margin of security beyond the catheter dead space is provided 1

Pediatric Considerations

For pediatric patients, withdraw 3-5 mL according to the catheter fill volume 1

Recent Research on Reduced Waste Volumes

While some recent studies suggest smaller waste volumes may be adequate, these findings should be interpreted cautiously for hemoglobin measurements:

• One study found 1.5 mL waste adequate for some parameters in triple-lumen CVCs 3
• Another study suggested 1 mL waste for peripheral IV catheters 4
• A pediatric study found 3 mL adequate for various CVC types 5

However, these studies have important limitations: They examined specific catheter types under controlled conditions and did not universally validate hemoglobin accuracy across all clinical scenarios 3, 4, 5

Clinical Implications of Inadequate Waste Volume

Failing to discard adequate waste volume will result in:

• Falsely low hemoglobin values due to hemodilution with flush solution 1
• Potential for inappropriate clinical decisions (unnecessary transfusions, incorrect anemia workup) 2
• Erratic or highly varying sequential test results that should raise suspicion of contamination 2

Contamination Risk with Different Flush Solutions

• Saline flush: Only gross contamination from poor technique causes significant errors 2
• Heparinized saline: Affects coagulation studies and other parameters 1, 6
• The type of flush solution determines the severity of potential contamination 2

Recommended Blood Draw Technique from PICC Lines

Follow this algorithmic approach:

1. Withdraw any heparin and saline from the catheter port per your facility protocol 1

2. Using sterile technique, withdraw 10 mL of blood from the catheter port in adults (3-5 mL in pediatrics) 1

   • This blood can be saved for reinfusion if desired, but must be discarded from the sampling pathway 1

3. Connect a new syringe or collection device and draw the sample for hemoglobin measurement 1

   • This ensures no dilution of the diagnostic sample 1

4. Flush the catheter with saline after completing the blood draw 7

Common Pitfalls to Avoid

• Never skip the waste volume assuming the catheter was recently flushed—residual solution remains in the dead space 1
• Do not reduce waste volume arbitrarily based on concerns about blood conservation without validating accuracy for your specific catheter and clinical context 1
• Suspect sample contamination when you see unexpectedly low hemoglobin values or erratic results between sequential draws 2
• Ensure adequate drying time if using alcohol-based skin preparation before accessing the catheter to prevent blood contamination 7