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Why doesn't my clinic do my blood draw through a port?


Updated January 24, 2011

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Question: Why doesn't my clinic do my blood draw through a port?

I'm tired of getting stuck for blood draws through my veins for CBCs. I have a port for chemo infusions, but my clinic never uses it for blood draws. Why don't they take a blood sample through a port?


Ports can contain substances other than blood. A contaminated blood draw results in an inaccurate blood count.

Infusion ports (also called Central Venous Access Device or CVAD) and PICC lines are great devices for all kinds of infusions. They consist of a soft, flexible catheter (tube) that is threaded through your vein and connected to a silicone balloon (lumen). Infusion needles can easily be inserted into a port without the pain and uncertainty of a vein puncture. Less pain and lots of convenience, right? So why not skip the hunt for a hand, arm, or inner elbow vein for a blood draw, and just use the port?

Blood Circulation 101

Your veins are lined with valves -- sometimes called gates -- that work a bit like subway turnstiles. Veins are a one-way highway taking blood from all over your body and moving it to your heart. The valves in your veins move blood cells against the pull of gravity, so that even blood from your feet, legs, and hands is circulated through your heart. Arteries move oxygen-rich blood out of your heart and transport it to your capillaries, where the oxygen is swapped for carbon dioxide. The capillaries act as sort of a transfer system, transporting the blood back to your veins. Blood circulation is a constant process.

Infusion Port Maintenance

When you have an infusion, your nurse will insert a needle in your vein or port, and saline will be dripped, to keep your vein open. Medications to prevent side effects may be given, and then chemotherapy drugs will be given through the silicone balloon of your port. Saline or Heparin will be used to flush your port after an infusion, but it may not do a perfect job.

Port Lurkers

Because a port is sort of a waystation on the subway line of your circulation system, a certain amount of non-blood substances can remain in the silicone balloon or perhaps in the catheter line. When you go to your clinic for a blood draw, there may be a variety of things in your port:

  • Drugs
  • Saline
  • Infections
  • Uncirculated blood cells
  • Blood clots

Guidelines To Prevent Contaminated Blood Samples

If your blood draw is done through your port, it may be contaminated unless a special procedure is used to ensure a clean blood sample. A nurse or phlebotomist must be trained in the correct method of cleaning or flushing a port before it can be used. Some clinics and hospitals require a doctor's order authorizing the use of a port for a blood draw. There are clinical guidelines in place for managing and using infusion ports -- those guidelines are in place to guard your health and ensure accurate results when your port is used.


Chemotherapy and You: Support for People With Cancer. How is chemotherapy given? National Cancer Institute. Posted: 06/29/2007.

Managing central venous access devices in cancer patients: a clinical practice guideline. Agency for Healthcare Research and Quality. Last updated: March 14, 2008.

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