Measurement of functional fibrinogen levels using the Thrombelastograph.

STUDY OBJECTIVE: To validate a Thromboelastograph (Haemoscope Corporation, Niles, IL) assay for functional fibrinogen. DESIGN: Correlation study of the Thromboelastograph assay with two conventional fibrinogen assays by the standard Clauss method. SETTING: Research laboratory of a university medical center. PARTICIPANTS AND INTERVENTIONS: Blood samples were obtained from 19 healthy volunteers. MEASUREMENT AND MAIN RESULTS: Thromboelastograph assays, using heparinized whole blood from 19 healthy donors, indicated that reptilase-XIIIa mixture (Activatorf)-generated clot shear elasticity in dynes per square centimeter (Gf) correlated with fibrinogen (mg/dL). Blood from four donors was used to define the contribution of hematocrit (Hct) to Gf by titration with platelet-rich plasma. The Gf versus Hct gave linear correlations (r2 = 0.746) with Gf = 1258 - 17.8 x % Hct. A commercial collection of 19 normal, 10 borderline, and one deficient for functional fibrinogen-citrated plasmas was assayed for Gf after recalcification using Activatorf. Of the 30 plasma samples, four were from factor X- or factor VII-deficient donors and one was from a coumadin-treated donor. There was a linear correlation of Activatorf Gf with functional fibrinogen (r2 = 0.940) with Gf = -730 + 9.21 x fibrinogen (mg/dL). CONCLUSION: Thrombelastography with Activatorf may be used to determine fibrinogen levels in whole blood.

Thrombelastography monitoring of resistance to enoxaparin anticoagulation in thrombophilic pregnancy patients.

The anticoagulant effect of enoxaparin is readily observed by Thrombelastography (TEG), particularly on the reaction time (R) to form a clot, and is completely reversed by heparinase. In this study, recalcified citrated whole blood with heparinase (CNHR) and without (CNR), along with TEG R time, was used to derive a delta R (CNR-CNHR). This delta R (DeltaR) was then used to measure enoxaparin anticoagulation, which was correlated by linear regression (r(2)=0.806) with plasma anti-Xa in 48 thrombophilic pregnancy patients. In a follow up study whole blood from 15 thrombophilic and 15 normal pregnancy subjects was titrated ex vivo with enoxaparin and TEG DeltaR determined. Linear dose responses (all r(2)>0.9) of DeltaR versus plasma enoxaparin concentration were obtained for each subject. A large variation in slope was observed for both thrombophilic (>7 fold, 217 to 1,588 s DeltaR/unit anti-Xa) and normal (>3 fold, 788 to 2,758) pregnancy subjects. The average slope for the thrombophilic group (710 s DeltaR/unit anti-Xa) was significantly (P=0.002) lower than the normal pregnancy group (1,354 s), indicating resistance to enoxaparin anticoagulation in the thrombophilic group. This technique may help gauge the appropriate dose of enoxaparin for each individual, check for residual anticoagulation before invasive procedures, and perhaps help screen for thrombophilic subjects.