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Silica-based PTT Reagent for Factor VIII

From Carol Gizzi at Baycare in Florida, We perform the factor VIII assay with a silica activated APTT ( PTT) reagent. We monitor hemophilic patients. Recently we were asked to switch our reagent to a PTT reagent using ellagic acid as the activator. We do not understand the reason for the request. We thought the silica activated reagent was the most sensitive? Are we incorrect?

Hi, Carol, and thank you for your question. I know of no reason for switching from a silica-based to an ellagic acid-based PTT reagent for the routine monitoring of coagulopathies, and in particular for factor VIII. I attended the Mayo Laboratories Coagulation Conference last week and used the opportunity to discuss this with my colleague, Dave McGlasson, from Wilford Hall USAF Medical Center, who also checked with several reagent distributors, and none knew of any reason. You probably check PTT sensitivity for factor VIII as part of your reagent validation, this should be all you need. It is true that the International Society on Thrombosis and Haemostasis recommends silica-based PTT reagents for the detection of lupus anticoagulant, as they are more sensitive than ellagic acid-based reagents, however both should work fine for monitoring factor deficiencies. Geo.

Comments (3)
Factor Assays
Aug 18, 2012 11:41pm

Hi all. It is likely that the recommendation for Carol’s lab
Hi all. It is likely that the recommendation for Carol’s lab to switch to an ellagic acid based APTT reagent is related to the perception that ellagic acid reagents are relatively ‘insensitive’ to lupus anticoagulants (LA). Such reagents are now considered to be preferred as a general screening test system to avoid unwanted detection of ‘asymptomatic’ LA positive individuals and the downstream problems this will cause in terms of investigative follow up testing, patient anxiety, delays to surgery, etc. Moreover, an LA insensitive APTT reagent may be preferred for factor assay testing to avoid the influence of potential LA on factor assay results. However, it should be cautioned that not all ellagic acid APTT reagents are LA insensitive. In particular, both Actin FS and Actin FSL are ellagic acid based, but Actin FSL is not LA insensitive. I would recommend the following excellent reference for further reading: Kershaw G, Suresh S, Orellana D, Nguy YM. Laboratory identification of lupus anticoagulants. Semin Thromb Hemost. 2012 Jun;38(4):375-84. Thank you, Dr. F, and I’d like to add our recent article on this subject, Fritsma GA, Dembitzer FR, Randhawa A, Marques MB, Van Cott EM, Adcock-Funk D, Peerschke EI. Recommendations for appropriate activated partial thromboplastin time reagent selection and utilization. Am J Clin Pathol. 2012 Jun;137(6):904-8.

Aug 18, 2012 5:43am

Hi, “jlow.” That is true, it is likely that an ellagic acid-
Hi, “jlow.” That is true, it is likely that an ellagic acid-based PTT reagent would be less sensitive to lupus anticoagulant and therefore be preferred for routine heparin monitoring and for factor deficiency screens.

Aug 14, 2012 4:13pm

George, in your very interesting paper in AJCP recently, the
George, in your very interesting paper in AJCP recently, the recommendation was made that the screening APTT reagent (also for Factor assays) should be lupus insensitive.Therefore, if ActinFS was recommended (rather then ActinFSL) then I understand the rationale for changing APTT reagent for screens and factor assays.

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