Picture of a port and catheter

Do You Flush a Port Before Drawing Blood? A Nurse’s Guide

As a nurse, you’ve likely accessed implanted ports (port-a-caths) countless times. One question that often comes up in practice is “do we flush a port before drawing blood?” Yes — and there’s a clear rationale rooted in safety, patency assessment, and INS evidence-based practice.

Why Flushing Matters Before a Blood Draw

Flushing before drawing blood from a port isn’t just a procedural step — it’s a safety and quality measure. According to the Infusion Therapy Standards of Practice (9th Edition), clinicians should flush and aspirate to assess patency and catheter function prior to each use of a vascular access device, which includes blood sampling from central venous access devices such as implanted ports.

Flushing before a blood draw:

  • Confirms patency and correct positioning of the non-coring needle.
  • Clears residual heparin lock or saline in the catheter lumen.
  • Reduces risk of drawing diluted specimens or inaccurate lab results.

Step-by-Step: Flushing a Port Before Drawing Blood

⚠️ Always follow your facility’s policy and the ordering provider’s instructions. This overview aligns with INS best practices and common clinical protocols.

1. Prepare the Patient & Supplies

  • Explain the procedure and verify patient identity.
  • Perform hand hygiene and don sterile gloves and mask per policy.
  • Ensure all necessary supplies are within reach:
    • Sterile 0.9% sodium chloride syringes (≥10 mL)
    • Non-coring (Huber) needle and extension set
    • Appropriate antiseptic skin prep (chlorhexidine/alcohol)
    • Sterile dressing materials
    • Vacutainer/syringe system for collection

2. Aseptic Access of the Port

  • Cleanse the port site thoroughly with an antiseptic (e.g., chlorhexidine in alcohol) and allow to fully air dry, reducing infection risk and maximizing antiseptic effectiveness.
  • Insert the Huber needle perpendicular to the port septum until securely seated.

3. Verify Placement & Patency

  • Once accessed, gently aspirate with a 10 mL (or larger) syringe to confirm brisk blood return.
    • Good blood return indicates the catheter and needle are properly positioned and patent.

4. Flush Before Drawing Blood

Yes — flush before drawing blood.

  • Use a 10 mL or larger syringe with sterile normal saline.
  • Flush with 0.9% sodium chloride using a push-pause (pulsatile) technique — this helps dislodge any small fibrin or particulate matter and enhances lumen patency.
  • Typical flush volume before drawing labs is 10–20 mL of saline, depending on your facility policy and the length/size of the catheter.

💡 Avoid using smaller syringes — they generate higher pressures that may damage the catheter.

5. Draw the Blood Sample

  • After flushing and patency confirmation, withdraw a waste/“discard” volume (often 5–10 mL) into a separate syringe to clear residual saline or heparin from the lumen — this minimizes dilution of the sample.
  • Collect the ordered specimens in order of draw, labeling tubes at bedside.

6. Flush After Blood Collection

  • Once specimens are collected, flush the port again with saline (usual volumes range 10–20 mL) to clear any blood from the lumen.
  • If the port is not going to remain accessed (i.e., you’re de-accessing), lock with an appropriate solution per policy (saline or heparin lock if indicated).

7. Finish the Procedure

  • Remove the needle while maintaining positive pressure in the system if locking.
  • Apply a sterile dressing.
  • Dispose of sharps and document the procedure including:
    • Flush volumes
    • Patency and aspiration results
    • Blood draw details and outcomes

Key INS Principles to Remember

Patency Assessment Before Use

INS standards highlight that all vascular access device lumens — including implanted ports — should be flushed and aspirated for blood return before use (which includes blood draws, infusions, or medication administration). This assessment is essential to ensure safe and effective access.

Use Appropriate Technique

  • Always use a 10 mL or larger syringe to prevent excessive pressure.
  • Employ aseptic technique and appropriate skin antisepsis before any access.

Device-Specific Recommendations

Although the 9th Edition includes detailed standards for vascular access devices overall, available summaries confirm the principles of flushing, patency verification, sterile access, and competency assessment remain core to safe practice.

Practical Pearls for Nurses

✔ Never force flush if resistance is met — this may indicate occlusion or malposition.
✔ Keep syringes strictly dedicated (one for saline flushes, one for specimen draw).
✔ Coordinate with the laboratory regarding discard volumes and technique to avoid contaminated or diluted values.
✔ Regular competency assessments on port access and flushing help maintain safe practice.

In summary:
Yes — you do flush a port before drawing blood. This step ensures patency, clears residual lock solution, and optimizes specimen quality. Use a ≥10 mL syringe with sterile saline in a push-pause technique, verify blood return, draw your samples, then flush again after collection — all aligned with INS standards and good central line care practice.