From Enriqueta Coll:
Dear George, I work in a small laboratory. In some pre-op patients without a history of bleeding, we have had results of partial thromboplastin time (PTT) prolonged between 5–10 seconds’ differences patient vs. control when using Actin, but normal when using C.K. Prest. We perform all tests using a Stat 4 coagulometer.
Afraid to report a normal result in a patient who can have a factor deficiency, we had reported both results with an explanation to the doctor about the different sensitivity between reagents and we had recommended to further investigating the concentration of FVIII, IX and XI. The concentration of those factors was within the reference range in the only one patient that came back to do the test. We lost contact with the other patients and we don’t know what was the decision of the doctor regarded the surgery.
Can you give me some advice that helps us to provide a better report to our patients?
Hello, Enriqueta, and thank you for your question. Siemens manufactures both Actin FS® and Actin FSL®. Actin FS® and Stago’s C. K. Prest® are formulated with moderate concentrations of reagent phospholipid and are relatively insensitive to lupus anticoagulant (LA). They are designed to monitor unfractionated heparin therapy and to screen for single or multiple coagulation factor deficiency.
Siemens’ Actin FSL PTT reagent is formulated with low concentration phospholipid and is consequently sensitive to LA. Actin FSL is designed to screen for LA, and a prolonged Actin FSL result may indicate a coagulation factor deficiency, the presence of unfractionated heparin, or a LA, all of which require confirmation.
From your message, I’ll assume you are using Actin FSL (not Actin FS) and that the patients whose PTT results are prolonged by using Actin but are normal using CK Prest possess LAs. LA has a 1% to 2% prevalence in the general population, and most LAs are innocent, transient side effects of recent infections or certain drug therapies. This is why laboratories prefer LA-insensitive PTT reagents for coagulation factor screening and heparin monitoring. If you are using Actin FSL, I recommend you switch to a LA-insensitive reagent or simply test with CK Prest, reserving the Actin FSL for LA detection in response to a suspected thrombosis event, as may occur when LAs are chronic.
Another possibility exists: undocumented heparin. Inpatients may be receiving or may have recently received unfractionated heparin. Often nurses flush vascular access devices with heparin, causing a prolonged PTT. Many lab directors require a follow-up thrombin time; a prolonged thrombin time indicates the presence of heparin. In this instance, the heparin may be neutralized using Hepzyme or Hepsorb and the PTT may be performed on the neutralized plasma, or the PTT may just be repeated.
Finally, in any unexpected prolonged PTT result, I suggest a mixing study: mix the patient plasma 1:1 with fresh normal plasma such as Precision BioLogic Inc CRYOcheck™, and perform a follow-up PTT on the mix. Correction to within the normal range or to within 10% of the normal plasma PTT is evidence for a coagulation factor deficiency, and lack of correction points to an inhibitor such as LA. I hope this helps.