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PT Specimen Clotting: Cold Agglutinin?

From “Pathous222″

Greetings. We recently encountered a specimen problem. A 64 YO lady on coumadin for patent foramen ovale came in as an outpatient for a prothrombin time (PT). The blue top clotted. We recollected it, collecting two tubes this time. One clots and the other appears to be OK but the PT is greater than 109 sec. We ran the tube through the Sysmex for a platelet count and it was 56K;  the patient usually runs between 250-300K. We made a smear of the blue top and there was some fibrin at the feathered edge. Suspecting a cold agglutinin, we recollect once more and put the tube in a warm block for delivery. We unfortunately do not have a heat-regulated centrifuge to ensure keeping it body temp during centrifuging. This tube was not clotted grossly but once again the PT is greater than 109 sec. Platelet count is 86K and there are platelet clumps on the smear. Are there any options to get an acceptable specimen to perform a PT for this patient? Any assistance that you could give would be greatly appreciated.

Hello, and thank you for your question. I’m not convinced you are dealing with a cold agglutinin, as you don’t report any appearance of RBC agglutinates (clumps). Platelet satellitosis may be part of the picture, as it is occasionally seen in sodium citrate anticoagulant (blue-top), though platelets more often form satellite patterns in EDTA (lavender). However, satellitosis does not account for partial clotting, evidenced by the fibrin that accompanies the platelet clumps and the prolonged PT.

You’ve ruled out specimen collection errors, so I’m guessing your patient is receiving a treatment that  triggers or interferes with in vitro coagulation. I find no references, so I’ll float the theory that one of the pegylated drugs or a plasma expander could be the culprit. Alternatively, she may have developed a protein imbalance such as an M-protein spike interfering with the PT. I’ll need some support here from our regular participants!

Meanwhile, you need a way to accurately monitor your patient’s coumadin. The most accurate approach is to switch to the chromogenic X assay, whose therapeutic range is approximately 20-40% factor X. A quicker fix would be to send her to an anticoagulation service that features a point of care instrument that measures capillary blood.

Continue to watch this post, several of our contributors manage coagulation reference laboratories and are likely to have seen this before. Geo.

Comments (2)
Mar 10, 2011 5:28am

Follow-up on the patient in question. The patient was referr
Follow-up on the patient in question. The patient was referred to a hematologist whom I called to inform them of the workup that has occurred so far. With the repeated technical issues and the ongoing desire to get the patient properly anticoagulated, the hematologist switched the patient to Dabigatran. So, I guess we will never know what the answer to this curiosity but at least the patient is being treated for her underlying problem.

Jan 27, 2011 1:29pm

Thanks for your reply. I appreciate your input and we have s
Thanks for your reply. I appreciate your input and we have started to investigate some of your suggestions. Her cold agglutinin screen was negative. To address some of your thoughts;
There is no evidence of platelet satellitosis seen on the slides we have examined. We did not see any RBC agglutination on the slides. I followed up with the clinician and the patient is not on any of the type of medications you describe. We will evaluate for a possible paraprotein. Any additional suggestions from the experienced coagulation gurus out there would be greatly appreciated as this patient has become somewhat of an enigma for us.

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