Can the Viscoelastic Parameter α-Angle Distinguish Fibrinogen from Platelet Deficiency and Guide Fibrinogen Supplementation?

Abstract

Viscoelastic tests such as thrombelastography (TEG, Haemoscope Inc., Niles, IL) and thromboelastometry (ROTEM, Tem International GmbH, Munich, Germany), performed in whole blood, are increasingly used at the point-of-care to characterize coagulopathic states and guide hemostatic therapy. An algorithm, based on a mono-analysis (kaolin-activated assay) approach, was proposed in the TEG patent (issued in 2004) where the α-angle and the maximum amplitude parameters are used to guide fibrinogen supplementation and platelet administration, respectively. Although multiple assays for both the TEG and ROTEM devices are now available, algorithms based on TEG mono-analysis are still used in many institutions. In light of more recent findings, we discuss here the limitations and inaccuracies of the mono-analysis approach. Research shows that both α-angle and maximum amplitude parameters reflect the combined contribution of fibrinogen and platelets to clot strength. Therefore, although TEG mono-analysis is useful for identifying a coagulopathic state, it cannot be used to discriminate between fibrin/fibrinogen and/or platelet deficits, respectively. Conversely, the use of viscoelastic methods where 2 assays can be run simultaneously, one with platelet inhibitors and one without, can effectively allow for the identification of specific coagulopathic states, such as insufficient fibrin formation or an insufficient contribution of platelets to clot strength. Such information is critical for making the appropriate choice of hemostatic therapy.

Comparación preoperatoria entre pruebas de coagulación y tromboelastografía en pacientes con cirrosis hepática sometidos a trasplante hepático

“…Para precisar más este punto se debe señalar que el valor del ángulo alfa, y más aun la MA, dependen de la cantidad y función plaquetaria y de la concentración de fibrinógeno. Para discriminar entre ambos componentes es necesario medir fibrinógeno funcional en el TEG, agregando factor tisular e inhibidor plaquetario 19 . En este estudio se realizó solamente TEG monoanálisis, activado con caolín, sin fibrinógeno funcional ni inhibidor plaquetario, por lo cual no es posible discriminar acerca de cuál es el responsable de la alteración observada.…”

ROTEM for Diagnosing Hyperfibrinolysis in Patients on the Liver Transplant Waiting List

“…Levels of tissue plasminogen activity, plasminogen activator inhibitor, and anti-plasmin were used as markers of fibrinolytic activity. This has led to research in determining the best way to diagnose and treat hyperfibrinolysis, and authors have proposed transfusion algorithms based on early ROTEM parameters during liver transplant [11,12]. Recently, Abuelkasem et al, reported that FIBTEM is a more sensitive test for fibrinolysis than EXTEM [10].…”

Targeted Thromboelastographic (TEG) Blood Component and Pharmacologic Hemostatic Therapy in Traumatic and Acquired Coagulopathy

“…The slope of the curve caused by that movement to 20 mm on the y-axis is called the “alpha (α)-angle.” A software system calculates this angle between the slope and the aforementioned axis of time. It has been noted that the TEG system calculates, by default, the “α-angle” as the angle formed by the tangential line to the curve starting from the split point of the trace [61]. “K” and “α-angle” are interpreted correlatively and reflect clot kinetics or the rate of clot formation.…”

“…The relative contribution of fibrinogen and platelets as related to the α angle has been recently delineated by a number of publications. For example, Solomon et al state that the α angle reflects the combined effects of platelets and fibrinogen to clot formation [61]. Ellis and colleagues described in 2007 that the α angle is a reflection of the speed with which clot strength is increasing and the MA is the combined contribution of platelets and fibrin to clot strength [75] (Fig.…”

“…Solomon et al have most recently clarified the best test for assessing the need for fibrinogen and platelets. When available, the most accurate initial assessment for plasma fibrinogen contribution to clot strength would be the maximum amplitude functional fibrinogen (MAFF) on the TEG or the FIBTEM maximum clot firmness (MCF) on the ROTEM when combined with some form of platelet functionality [61, 79]. …”