Fibrin: Friend of Foe?
When you accidentally cut yourself or are bleeding from an injury, fibrin is your friend. It stops the bleeding and eventually forms a stable mat of tissue that seals the wound from infection while the damaged tissue regenerates. But when you pull red-top tubes from the centrifuge, the same fibrin is your foe. More accurately, it’s your patient’s foe. That’s because fibrin formation in the tube to be tested may lead to instrumentation problems and/or inaccurate results. To fight these threats of fibrin, let’s look at how it works against the patient in the clinical laboratory.
It’s not just clot tubes that are susceptible to fibrin formation. Fibrin can develop in all tubes because of one or more of the following conditions:
Overfilling collection tubes
Anticoagulant tubes are calibrated with the perfect amount of additive to maintain the proper blood:anticoagulant ratio when the tube is filled to +10% of its stated capacity. Overfilling tubes beyond 10% increases this ratio to a level that can lead to incomplete anticoagulation, and the formation of fibrin strands or clots. Make sure you fill all tubes to their stated volumes. Specimens that are overfilled should be discarded and recollected.
Premature centrifugation is the most common cause of post-centrifugation fibrin in serum samples. When prematurely centrifuged, clotting can continue long after centrifugation. Should such specimens be inadvertently tested, the continually forming fibrin can obstruct and/or disable sensitive laboratory testing instruments. Post-centrifugation fibrin formation can lead to instrument down time, which delays testing, potentially affecting patient care adversely. Worse, fibrin strands that don’t impede instrumentation can lead to erroneous results that go undetected and precipitate patient mismanagement.
Tubes with clot activators should be allowed to clot for 30 minutes. Contrary to popular belief, clot activators don’t accelerate clotting, they facilitate more complete clotting. Their real benefit is that they generate a cleaner, more fibrin-free serum sample, one less likely to cause instrumentation problems or threaten result accuracy. Although clot activators cause clot tubes to gel up faster, manufacturers will tell you such tubes still require 20-30 minutes for clotting to complete. Allowing all tubes without anticoagulants to clot in an upright position for 30 minutes prior to centrifugation is the best way to prevent fibrin from threatening instrumentation and test accuracy.
Not only does premature centrifugation incorporate delays in testing due to recentrifugation and increased handling, the physical removal of fibrin can potentially expose the processor to bloodborne pathogens. When necessary, fibrin may be removed with wooden applicators and discarded into a biohazardous waste receptacle. However, whenever stoppers are removed, proper personal protection equipment must be used including face protection, gloves, and a closed lab coat.
Delayed or prolonged coagulation can result in fibrin formation well beyond the 30-minute recommendation for pre-centrifugation clotting. Blood from patients on anticoagulant therapy or with coagulopathies can continue to clot long after centrifugation, even throughout serum storage. As in premature centrifugation, delayed or prolonged clotting may continue into the analytical phase and cause the same instrumentation malfunctions and erroneous results. Such specimens must be closely monitored throughout the preanalytical and analytical phases. If the test methodology permits, plasma samples may be considered as an alternative in order to eliminate the potential problems post-centrifugation fibrin formation can cause.
Improper mixing with additives
Failure to properly and timely mix tubes with anticoagulants can lead to fibrin formation as well. When additives are not well mixed with the specimen, fibrin can precipitate before, during and after centrifugation. Even plasma tubes must be inspected for fibrin formation prior to testing. To prevent fibrin formation due to improper mixing, all tubes should be inverted immediately upon filling according to the manufacturer’s recommended number of inversions.
Center Announces Free Products/Services
Starting this month, visitors to the Center’s homepage will find a link to a free article posted monthly or bi-monthly, depending on how well it is received. We’ll start with some interesting interviews we’ve had through the years, too intriguing to be buried in our archives forever, then see how it goes. They’ll be yours to read, share, learn from, print, and file for future reference. And that’s just the beginning. Every package we ship out will now come with a free, colorful bookmark listing the proper order of draw, something we consider to be phlebotomy’s best-kept secret. Not that the order of draw is a secret, but the proper order as recommended by CLSI is greatly misrepresented on the Internet and in some publications.
Also, be on the lookout for an online community our web site will be hosting. Healthcare professionals around the world can gather; discuss technical concerns; the issues of the day pertaining to the field; or share their ideas, successes, and frustrations. It’s still a month or so away, but it’s in the pipeline and it will be free.
Center Makes Free Shipping Permanent
Due to an overwhelmingly positive response to its free shipping offer for July, the Center for Phlebotomy Education is making it permanent! Shipping charges will be automatically waived on all orders over $50. All purchases qualify including online orders, purchase orders, phone orders, or orders received by mail. For a catalog of all phlebotomy education products, visit the Center for Phlebotomy Education's catalog at www.phlebotomy.com/Products.html.
This Month in Phlebotomy Today
Hereís what subscribers to Phlebotomy Today, the Center for Phlebotomy Educationís paid-subscription newsletter currently in its 8th year of publication, are reading about this month:
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Featured FAQ: Discard volumes
Question:Can you give a "nurse friendly" definition of line deadspace and wouldn't saying "six times the deadspace" be more accurate than just saying "5 mL"? Next, what would you consider the lesser of 2 evils for clearing deadspace - drawing a red-top with sprayed with clot activator first , or drawing an extra coag tube (if that is the first tube to be collected)? The problem is that we just switched to a low volume coag tube (2.7 mL) and that would not be enough volume to clear the deadspace.
Response:The deadspace volume is that volume of fluid that the line holds between where a syringe would be attached to withdraw the blood out and the aperture that opens up into the bloodstream. The reason we say a 5 mL discard is usually enough is that those who draw blood from vascular access devices don't always know the device's dead space volume and researching it would take too much valuable time. So as a general rule, if you discard 5 mL, that's usually at least six times the dead space volume of most vascular access devices.
You are correct that a low-volume coag tube wouldn't be enough to clear the recommended dead space volume. If you are drawing with a syringe, of course, you'd simply discard the entire syringe. But if you're drawing from a VAD with a tube holder in which the entire vacuum of the tube is applied to the opening of the lumen, you could be risking hemolysis if the VAD is smaller than, say, 18 gauge. So I would suggest doing all your draws from VADs with syringes instead of tube holders so that the pressure at the tip of the line is minimal and less likely to rupture red cells.
If you still want to apply a tube holder and draw directly into tubes, be prepared for specimen rejection. If it occurs too frequently, switch to syringes. Nevertheless, if you're drawing directly into tubes, and a coag tube is required, it's not advisable to draw into a clot activator tube as a discard tube since it is conceivable that some of the activator can carryover into the coag tube and corrupt the results. Instead, use two low-volume coag tubes or a plain non-additive tube, but not a clot activator tube. Clot activators are considered additive tubes, too. Hope this helps.
Each month, PT—STAT! will publish one of the hundreds of phlebotomy FAQs in the growing database of questions and answers available in Phlebotomy Central, the members-only section of the Center for Phlebotomy Education's web site. For information on joining Phlebotomy Central, visit www.phlebotomy.com/PhlebotomyCentral.html.
Specimen Collection Safety: single-use tube holders
Do you remove the needle from the syringe or tube holder before discarding?
The act of removing the needle from the drawing device is against OSHA regulations. Discarding needle/syringe or needle/tube holder assemblies as one unit minimizes the risk of exposure significantly, not only for the user, but for the downstream waste handler.
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