laboratory of blood coagulation
Contributions
Type: Publication Only
Background
Resistance to activated protein C (APCR) is associated with high risk of venous thromboembolism (VTE). After the factor V Leiden (FVL) mutation was found as the main cause of APCR little attention is paid to the role of acquired APCR. An acquired resistance to activated protein C has been previously shown in patients with antiphospholipid antibodies. The Calibrated Automated Thrombography (CAT) is now considered to reflect patients phenotype better than traditional coagulation tests. When thrombomodulin (TM) is used thrombin generation (TG) becomes sensitive to all disorders of the PC system.
Aims
Aim of our study was to evaluate the prevalence of acquired APCR and its reasons in patients with VTE manifestation under the age of 45 years.
Methods
The study involved 35 patients (M/F 15/20, mean age 37,0±9,0 yr) with early manifestation of VTE and 30 controls. All patients received vitamin K antagonists (VKA) treatment at least for 6 months, 18 of them were still on VKA. TG was measured according to Hemker et al. with fluorogenic assay, at 5 pM TF and 4 μM phospholipids in platelet poor plasma (PPP) with PPP plasma+/-TM reagent (Thrombinoscope BV, Maastricht, The Netherlands).
Results
Endogenous thrombin potential (ETP) and peak thrombin (PT) were markedly reduced in the presence of TM. None of the patients had increased ETP measured as values above 95th percentile in controls (i.e. >2114 nMmin in the absence of TM and >1433 nMmin in the presence of TM). Lupus anticoagulants (LA) were found in 5 patients. From parameters derived from the thrombin generation curves measured both with and without TM significant correlation with LA (p<0,05) was found for lag-time (R=0,45), ETP (R=-0,45) and PT (R=-0,44) both in presence and absence of TM. Normal ranges of ETP and PT inhibition calculated in controls were 21-62% and 14-51% respectively. Values below 21% for ↓ETP and/or 14% for ↓PT (i.e. APRC) were found in 20 (57%) of samples. In the studied group 100% of patients with FVL demonstrated APCR phenotype. So, in 50 % of cases APCR was due to FVL mutation (10 patients, among them 2 patients with acquired protein C deficiency on VKA treatment). As for the rest 50 % of detected APCR cases 25 % (5 patients) were associated with LA, 10 % (2 patients) with isolated increased FVIII activity, 10 % (2 patients) with prothrombin G20210A mutation and increased FVIII activity. The reasons of APCR in the rest 5 % of cases need further elucidation. APCR was found in 100% of LA samples. Importantly all these patients had protein C activity within the normal range. Abnormal PT inhibition seemed the most sensitive to detect APCR. Abnormal PT inhibition was found in all patients, contrary to ETP inhibition - 50% cases with FVL and 75% with LA.
Summary
In conclusion LA was the most prevalent cause of acquired APCR in our patients. Beta2 glycoprotein I, anti-prothrombin antibodies and lupus anticoagulants previously demonstrated association with APCR, determined by classic activated partial thromboplastin time-based tests. We used a novel integrated approach with calibrated automated thrombography made in parallel with and without TM. This modification of the thrombin generation test allows effectively detecting APCR and LA even in patients on vitamin K antagonists treatment, that is very important for clinical practice. APCR in patients with lupus anticoagulants is strongly associated with thrombotic complications; it was demonstrated by CAT in all patients with VTE manifestation under the age of 45 years and LA laboratory phenotype. Acquired APCR could be the main pathogenic mechanism underlying thrombosis associated with LA.
Keyword(s): Activated protein C, Antiphospholipid antibody, Thrombin generation, Thrombosis
Session topic: Publication Only
Type: Publication Only
Background
Resistance to activated protein C (APCR) is associated with high risk of venous thromboembolism (VTE). After the factor V Leiden (FVL) mutation was found as the main cause of APCR little attention is paid to the role of acquired APCR. An acquired resistance to activated protein C has been previously shown in patients with antiphospholipid antibodies. The Calibrated Automated Thrombography (CAT) is now considered to reflect patients phenotype better than traditional coagulation tests. When thrombomodulin (TM) is used thrombin generation (TG) becomes sensitive to all disorders of the PC system.
Aims
Aim of our study was to evaluate the prevalence of acquired APCR and its reasons in patients with VTE manifestation under the age of 45 years.
Methods
The study involved 35 patients (M/F 15/20, mean age 37,0±9,0 yr) with early manifestation of VTE and 30 controls. All patients received vitamin K antagonists (VKA) treatment at least for 6 months, 18 of them were still on VKA. TG was measured according to Hemker et al. with fluorogenic assay, at 5 pM TF and 4 μM phospholipids in platelet poor plasma (PPP) with PPP plasma+/-TM reagent (Thrombinoscope BV, Maastricht, The Netherlands).
Results
Endogenous thrombin potential (ETP) and peak thrombin (PT) were markedly reduced in the presence of TM. None of the patients had increased ETP measured as values above 95th percentile in controls (i.e. >2114 nMmin in the absence of TM and >1433 nMmin in the presence of TM). Lupus anticoagulants (LA) were found in 5 patients. From parameters derived from the thrombin generation curves measured both with and without TM significant correlation with LA (p<0,05) was found for lag-time (R=0,45), ETP (R=-0,45) and PT (R=-0,44) both in presence and absence of TM. Normal ranges of ETP and PT inhibition calculated in controls were 21-62% and 14-51% respectively. Values below 21% for ↓ETP and/or 14% for ↓PT (i.e. APRC) were found in 20 (57%) of samples. In the studied group 100% of patients with FVL demonstrated APCR phenotype. So, in 50 % of cases APCR was due to FVL mutation (10 patients, among them 2 patients with acquired protein C deficiency on VKA treatment). As for the rest 50 % of detected APCR cases 25 % (5 patients) were associated with LA, 10 % (2 patients) with isolated increased FVIII activity, 10 % (2 patients) with prothrombin G20210A mutation and increased FVIII activity. The reasons of APCR in the rest 5 % of cases need further elucidation. APCR was found in 100% of LA samples. Importantly all these patients had protein C activity within the normal range. Abnormal PT inhibition seemed the most sensitive to detect APCR. Abnormal PT inhibition was found in all patients, contrary to ETP inhibition - 50% cases with FVL and 75% with LA.
Summary
In conclusion LA was the most prevalent cause of acquired APCR in our patients. Beta2 glycoprotein I, anti-prothrombin antibodies and lupus anticoagulants previously demonstrated association with APCR, determined by classic activated partial thromboplastin time-based tests. We used a novel integrated approach with calibrated automated thrombography made in parallel with and without TM. This modification of the thrombin generation test allows effectively detecting APCR and LA even in patients on vitamin K antagonists treatment, that is very important for clinical practice. APCR in patients with lupus anticoagulants is strongly associated with thrombotic complications; it was demonstrated by CAT in all patients with VTE manifestation under the age of 45 years and LA laboratory phenotype. Acquired APCR could be the main pathogenic mechanism underlying thrombosis associated with LA.
Keyword(s): Activated protein C, Antiphospholipid antibody, Thrombin generation, Thrombosis
Session topic: Publication Only