Preparing PPP

From Rebecca Jones, Trinity Medical Center, Birmingham:

Hey George, love the website! If only all disciplines had access to all this knowledge! Thanks for all you do.

I have another question for you to ponder…or not. What is your feeling about performing a “hard spin” on coagulation specimens? We do a “quick spin” for 2–3 minutes and then do prothrombin times (PT), partial thromboplastin times (PTT), fibrinogens, and D-dimers. The only reference in CLSI documents (specifically D-dimer) states that the recommendation is a slower spin to have platelet poor plasma. These small stat centrifuges are giving platelet poor plasma, however I need some reassurance. Especially if I start adding more special coagulation to my in house menu. Thanks again!

Also an update on the Plavix question. We are still using the VerifyNow. We gave the physicians a percent inhibition guide when releasing the new PRU value. We’ve received only three phone calls so far with physicians needing help interpreting. We are considering moving Plavix to the TEG and adding PFA and other testing as well. We have a TEG on site and are currently monitoring heparin in surgery with it. More to come on that project later.

Hi, Rebecca and thank you for the compliment. Rebecca is a graduate of our UAB Masters in Clinical Laboratory Science program, and I had the pleasure of working with her in the graduate program and in UAB Hematology laboratory. Thank you for the update on the VerifyNow report, it may be that others would like to learn how you are managing your reports during the switch-over to PRUs. Also, the Thromboelastograph (TEG) appears to be a good substitute and is getting a lot of attention.

The small desk-top centrifuges, such as the Stat-Spin Express, do a fine job of producing platelet-poor plasma (PPP, plasma whose platelet count is <10,000/μL). There is one caveat. Because they are angle-head centrifuges, the platelets tend to adhere to the side of the tube and slowly release back into the plasma. So, you can’t let them stand more than an hour or so before testing. You can determine the exact time limit with a simple experiment: just count the plasma at regular intervals to record a rise.

The Stat-Spin centrifuges have limited capacity, however, so you may want to have a larger centrifuge for big batches. Choose a centrifuge with swinging heads that leave behind a level interface. If you have a centrifuge capable of reaching 8000 RPM, you can prepare PPP in 2–3 minutes that is adequate for your routine testing.

For special coagulation testing, for example, factor assays or lupus anticoagulant profiles, most lab directors require double-spinning in accordance with CLSI H21. Spin for 10 minutes at 2500 g (g-force, not RPM), separate the plasma, and spin the plasma at 2500g for an additional 10 minutes. With this technique, the plasma platelet count ends up usually at <5,000/µL. You should also choose this approach if you plan to freeze the specimen. I hope this helps!