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(Editor's note: This article originally appeared in Phlebotomy Today-STAT!, a free e-newsletter from the Center for Phlebotomy Education Inc. Reprinted with permission. For more information, visit http://www.phlebotomy.com/.)
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,
- premature centrifugation,
- improper mixing or
- incomplete clotting.
Overfilling Collection Tubes
Anticoagulant tubes are calibrated with the perfect amount of additive to maintain the proper blood-to-anticoagulant ratio when the tube is filled to 10 percent of its stated capacity.
Overfilling tubes beyond 10 percent 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
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.
Incomplete Clotting
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.
Upright is Right
When serum tubes are filled and not placed upright in a rack while clotting takes place, fibrin can adhere to the stopper as it forms. Centrifugation may not be enough to dislodge it, leaving strands in the serum after centrifugation is complete. To avoid this scenario, always stand serum tubes upright in a tube rack so clotting occurs without blood to stopper contact.
Should you ever cut yourself or otherwise need the coagulation cascade to commence within you, fibrin can be a friend in need. But should you fail to handle serum samples from the patients you draw properly, it's a foe, indeed.
Dennis J. Ernst is the executive director of the Center for Phlebotomy Education Inc., Corydon, IN.
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