From Michelle Fahs, MT (ASCP), Clinical Laboratory Educator, Mercy Hospital St. Louis School of CLS.
George, Do you have any recommendations on how the sample should be collected for coag testing if the patient’s hematocrit is >55%? We have in our policy the formula and procedure for adjusting the amount of anticoagulant in the tube to obtain the 9:1 ratio of blood to anticoagulant, but once we break the vacuum seal on the vacutainer tube to adjust the anticoagulant volume it cannot be filled without using a syringe. Since the risk of the sample clotting or hemolyzing is greater when using a syringe to draw the blood, we don’t recommend that either. Any suggestions? Thanks for your help.
Hi, Michelle, I was in Bangor, Maine conducting a seminar today and I tried your question on the audience. They only know of one way to accomplish this, which is to use a syringe, as you suggest. I knew of one lab scientist many years ago who claimed to be able to remove the precise volume without breaking the vacuum by withdrawing a tiny amount of citrate using a tuberculin syringe, but I never actually saw her do it. You can minimize potential clotting by transferring immediately after collection, and gentle withdrawal usually prevents hemolysis. Of course, you must use a safety needle that can be removed without risk of injury prior to transfer.
Strongly disagree with the
Strongly disagree with the statement that “…the risk of the sample…hemolyzing is greater when using a syringe to draw the blood…” Direct comparison of both methods showed rather the opposite effect:
Evaluation of sample hemolysis in blood collected by S-Monovette using vacuum or aspiration mode. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3900093/.
The use of S-Monovette is effective to reduce the burden of hemolysis in a large urban emergency department. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4401311/
In order to prevent blood activation and clot formation in the syringe, it can be prefilled with a corrected amount of citrate and then mixed blood specimen with citrate to be transferred from syringe to empty blue top tube.
If an over-citrated specimen (due to high hematocrit or short draw) cannot be recollected appropriately, the laboratory specialist could try the below-mentioned approach, however this is unknown if it’s also valid in other coagulation tests besides APTT):
Usefulness of high-concentration calcium chloride solution for correction of activated partial thromboplastin time (APTT) in patients with high hematocrit value. http://www.ncbi.nlm.nih.gov/pubmed/17904620
This is indeed a tricky
This is indeed a tricky maneuver. The CLSI coag standard (H21) has a chart that tells you how much sodium citrate is required based on the patient’s hematocrit, and states “Place the volume (of anticoagulant) in a collection tube and add blood up to the required total volume.” This seems to require knowledge of the patient’s hematocrit in advance of the coag collection, and the use of a syringe to transfer the blood to the “doctored” citrate tube. That’s not the ideal solution, but I’m afraid there is no ideal solution.
In the February 2005 issue of MLO, an article titled “Under the Blue Top: Coags, Corrections, and Crits” explains an alternative method this way:
“The cap should be removed and the tube filled by syringe to a level 8 mm from the top edge of the tube. Then, the tube should be recapped, but not with the original cap; the overfill will not allow a hemogard tube to be re-fit. Our laboratory uses the small plastic caps (BD#B3035-80 through 86), and the bottom of the cap, when placed on the tube, is exactly where the level of the blood should be. Any more detailed manipulation of citrate or blood levels based on actual hematocrits is probably not worth the effort and may cause more error than it attempts to cure.”
Here’s a link to the article, which appears on Page 20. http://www.mlo-online.com/articles/200502/0205clinical_issues.pdf I hope this helps.
Agree with George. I think it
Agree with George. I think it is theoretically possible to draw out a small amount of citrate with a fine needle system without ‘breaking’ the vacuum in a tube system , but this will be a frustrating (and potentially injurious) process for many, and so most operators will need to revert to the open tube, then syringe and needle method; the latter is becoming a dwindling art-form not only because the vacuum systems predominate, but also for ‘Work, Health & Safety’ reasons. I will also add that there is increasing complexity these days because of specialization–the collectors (called phlebotomists these days) are usually different people to those that process the sample (‘specimen reception/management’) and different again to those that do the tests. Many hands used to make light work; these days, many hands complicate the process!