Apixaban plasma concentrations in patients with obesity.

PURPOSE: Routine therapeutic drug monitoring of apixaban is currently not recommended but may however be warranted in some situations and for some patient groups to provide better and safer treatment. Due to limited data on apixaban concentrations in different subpopulations, it is still unclear which group of patients could possibly gain from monitoring. The purpose of this study was to examine apixaban exposure in patients with obesity compared with normal-weight patients. METHODS: Forty patients with obesity (mean BMI 39.4 kg/m2) and 40 controls with normal weight (mean BMI 23.4 kg/m2), treated with apixaban 5 mg twice daily were included. The patients were matched for age, sex, and renal function. Trough and peak apixaban concentrations were measured with LC‒MS/MS methodology. RESULTS: The median trough concentrations in patients with obesity (58.7, range 10.7-200.7 ng/ml) were slightly higher than those in patients with normal weight (52.0, range 31.0-150.9 ng/ml) (p < 0.05). Notably, the variability in trough concentration was considerably higher in patients with obesity. Peak concentrations were similar in both groups, with a median of 124.5 ng/ml (range 82.0-277.5) and 113.5 ng/ml (range 75.5-334.6) in patients with obesity and normal weight, respectively. CONCLUSION: Apixaban exposure did not vary substantially between obese and normal weight matched controls, implying that general dose adjustments are not required. However, vast interindividual variability was observed in patients with obesity, suggesting that measuring the concentrations could be valuable for specific patients. Further research is needed to identify which specific patients may benefit from this approach.

Effects of dabigatran, rivaroxaban, and apixaban on fibrin network permeability, thrombin generation, and fibrinolysis.

INTRODUCTION: There are important pharmacological differences between direct oral anticoagulants (DOAC) and a deeper knowledge of how they influence different aspects of hemostasis in patients on treatment is desirable. MATERIALS AND METHODS: Blood samples from patients on dabigatran (n = 23), rivaroxaban (n = 26), or apixaban (n = 20) were analyzed with a fibrin network permeability assay, a turbidimetric clotting and lysis assay, the calibrated automated thrombogram (CAT), plasma levels of thrombin-antithrombin complex (TAT) and D-dimer, as well as DOAC concentrations, PT-INR and aPTT. As a comparison, we also analyzed samples from 27 patients on treatment with warfarin. RESULTS: Patients on dabigatran had a more permeable fibrin network, longer lag time (CAT and turbidimetric assay), and lower levels of D-dimer in plasma, compared with patients on rivaroxaban- and apixaban treatment, and a more permeable fibrin network than patients on warfarin. Clot lysis time was slightly longer in patients on dabigatran than in patients on rivaroxaban. Warfarin patients formed a more permeable fibrin network than patients on apixaban, had longer lag time than patients on rivaroxaban (CAT assay), and lower peak thrombin and ETP compared to patients on treatment with both FXa-inhibitors. CONCLUSIONS: Results from this study indicate dabigatran treatment is a more potent anticoagulant than apixaban and rivaroxaban. However, as these results are not supported by clinical data, they are probably more related to the assays used and highlight the difficulty of measuring and comparing the effect of anticoagulants.

Clinical evaluation of laboratory methods to monitor exposure of rivaroxaban at trough and peak in patients with atrial fibrillation.

PURPOSE: The one-dose daily regime of rivaroxaban could cause a pronounced variability in concentration and effect of which a deeper knowledge is warranted. This study aimed to evaluate the typical exposure range and effect of the direct factor Xa (FXa)-inhibitor rivaroxaban in a cohort of well-characterized patients with atrial fibrillation (AF). METHODS: Seventy-one AF patients (72 ± 8 years, 55 % men) were treated with rivaroxaban 15 mg/20 mg (n = 10/61) OD. Trough (n = 71) and peak (n = 30) plasma concentrations determined by liquid chromatography-tandem mass-spectrometry (LC-MS/MS) were compared to the coagulation assays anti-FXa for rivaroxaban, prothrombin time-international normalized ratio (PT-INR) (venous samples and point-of-care assay (POC) CoaguChek XS Pro), and aPTT. RESULTS: Median rivaroxaban plasma concentrations by LC-MS/MS were 34 (range 5-84) and 233 ng/ml (range 120-375) at trough and peak, respectively. A strong correlation between LC-MS/MS and the anti-FXa assay was found (p < 0.001) for both trough (r (2) = 0.92) and peak (r (2) = 0.91) samples. PT-INR results from the POC assay, but not from the conventional PT assay, correlated significantly with LC-MS/MS in peak samples exclusively (r (2) = 0.41, p < 0.001). CONCLUSIONS: In "real-life" AF patients treated with rivaroxaban, we observed a pronounced variability in plasma concentrations at trough and to a lesser extent at peak measured by LC-MS/MS. The anti-FXa assay performed well upon rivaroxaban levels in a normal exposure range, although LC-MS/MS remains the only method that covers the whole concentration range with accuracy. Interestingly, the POC assay for PT-INR could be useful to indicate high exposure to rivaroxaban in emergency situations although further validation is required.

Evaluation of coagulation assays versus LC-MS/MS for determinations of dabigatran concentrations in plasma.

BACKGROUND: Dabigatran is an oral direct thrombin inhibitor for which routine laboratory monitoring is currently not recommended. However, there are situations in which measurements of the drug and its effect are desirable. We therefore compared and validated different coagulation methods for assessments of dabigatran in clinical samples in relation to measurements of plasma dabigatran, without the purpose of establishing effective and safe concentrations of dabigatran in plasma. METHODS: Samples were obtained from 70 atrial fibrillation patients treated with dabigatran etexilate. Plasma concentrations were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and were compared with coagulation methods Hemoclot thrombin inhibitors (HTI) and Ecarin clotting assay (ECA), as well as with prothrombin time-international normalized ratio (PT-INR) and activated partial thromboplastin time (aPTT). RESULTS: A wide range of dabigatran concentrations was determined by LC-MS/MS (<0.5-586 ng/mL). Correlations between LC-MS/MS results and estimated concentrations were excellent for both HTI and ECA overall (r(2) = 0.97 and 0.96 respectively, p < 0.0001), but the precision and variability of these assays were not fully satisfactory in the low range of dabigatran plasma concentrations, in which ECA performed better than HTI. aPTT performed poorly, and was normal (<40 s) even with dabigatran levels of 60 ng/mL. PT-INR was normal even at supratherapeutic dabigatran concentrations. CONCLUSION: LC-MS/MS is the gold standard for measurements of dabigatran in plasma. Alternatively, either HTI or ECA assays may be used, but neither of these assays is dependable when monitoring low levels or to infer total absence of dabigatran. The aPTT assay is relatively insensitive to dabigatran, and normal aPTT results may be observed even with therapeutic dabigatran concentrations.

Rapid Detection of Apixaban by a ROTEM-Based Approach and Reversibility with Andexanet Alfa or DOAC-Stop.

Background A rapid test to detect apixaban treatment would be useful in acute situations such as major bleeding, urgent surgery, or in acute thrombosis. Objective This article aims to study if the viscoelastic test rotational thromboelastometry (ROTEM) can rapidly detect apixaban in whole blood using modified triggers based on factor Xa (FXa) or Russell viper venom (RVV). Method ROTEM clotting time (CT) was measured in samples from 40 patients on apixaban treatment, and in vitro in samples spiked with apixaban (20-500 ng/mL). Commercially available trigger Ex-tem was compared with modified triggers based on FXa or RVV. Reversibility of apixaban in the samples was studied; CT was measured with and without addition of DOAC-Stop or andexanet alfa, respectively, and the difference in CT was calculated (CT diff ). Results Using FXa as trigger, we detected apixaban concentrations at 20 ng/mL and above with 100% sensitivity and 100% specificity in patient samples and in vitro. Corresponding data for Ex-tem were 92% sensitivity and 100% specificity in patients, and 94% sensitivity and 100% specificity in vitro, and for RVV 97% sensitivity and 94% specificity in patients, and 97% sensitivity and 100% specificity in vitro, respectively. CT diff data were similar. Patient sample data were obtained within 20 minutes from sampling. Conclusion Apixaban at low therapeutic concentrations was detected within 20 minutes, and with high sensitivity and specificity. A trigger based on FXa outperformed the commercial trigger Ex-tem and a trigger based on RVV. ROTEM with a FXa-based trigger is a promising method to detect apixaban bedside in acute settings.

A global assay of haemostasis which uses recombinant tissue factor and tissue-type plasminogen activator to measure the rate of fibrin formation and fibrin degradation in plasma.

The global assay of Overall Haemostasis Potential we previously described has been refined. The coagulation cascade in platelet-poor plasma is triggered by adding a minimal dose of recombinant tissue factor together with purified phospholipids and calcium; fibrinolysis is initiated by adding recombinant tissue type-plasminogen activator in a concentration similar to what can be obtained during thrombolysis. Numerical differentials of optical densities reflecting rates of fibrin formation and degradation are calculated by a new software, and the Coagulation Profile (Cp) and the Fibrinolysis Profile (Fp) are determined. The combined effect of these counteractive systems is expressed as a ratio of Cp to Fp, called the Overall Haemostasis Index. Commercially available coagulant-deficient patient plasma samples and plasma with various amounts of added PAI-1 are examined; changes of fibrin turbidity demonstrate that this assay can determine Cp and Fp in a physiologically relevant way. Increased Cp and decreased Fp in prothrombotic patients, as well as expected effects of heparin or a thrombin inhibitor on Cp and Fp, suggest that our method can detect hypercoagulability and assist in monitoring antithrombotic treatment. Ongoing studies will show whether this simple assay can be of value in clinical routine.

Comparison of two immunochemical assays for measuring thrombin-activatable fibrinolysis inhibitor concentration with a functional assay in patients with acute coronary syndrome.

TAFI was measured as relative activity concentration (Pefakit) and antigen concentration (Haemochrom and Asserachrom) both acutely and during convalescence in patients suffering from acute coronary syndrome, and in a group of healthy controls. There was a rather weak but significant correlation between the activity and antigen concentrations. The results obtained by the Haemochrom method, assumed to measure the concentrations of all forms of TAFI, were lower than those by the Asserachrom method although the latter is assumed to only measure the pro-TAFI concentration. Both immunoassays gave lower results than the functional method (Pefakit). The patients in the convalescence phase showed a higher activity concentration than the healthy controls. The Asserachrom showed a higher concentration in the acute and convalescence phases of the patients compared to the controls, whereas the Haemochrom did not show any such difference. This could be related to different species of the TAFI molecule and thus different reactivity to the antibodies. Therefore the optimal choice of assay for determination of TAFI in different clinical studies is of importance. The Pefakit and Asserachrom seem to be appropriate candidates.

Effects of direct oral anticoagulants on lupus anticoagulant assays in a real-life setting.

Laboratory diagnosis of lupus anticoagulant (LA) is based on prolongation in at least one coagulation assay (diluted Russell's viper venom time - dRVVT or activated partial thromboplastin time - aPTT), which normalises after addition of phospholipids. Both assays may be influenced by anticoagulants and therefore LA should not be tested during warfarin or heparin treatment. It has been shown (primarily in vitro) that direct oral anticoagulants (DOACs - dabigatran [DAB], rivaroxaban [RIV] and apixaban [API]) may also influence LA testing. We tested the effects of DOACs on assays routinely used for the diagnosis of LA in patients treated with these drugs in a real-life setting. Plasma from patients with atrial fibrillation treated with DAB (n=30), RIV (n=20) and API (n=17) and not known to have LA were tested using dRVVT (LA-screen and LA-confirm, Life Diagnostics) and aPTT (PTT-LA, Diagnostica Stago and aPTT Actin FS, Siemens Healthcare Diagnostics) assays. According to the diagnostics algorithm, dRVVT and aPTT ratios of <1.2 were considered negative, ratios of >1.4 positive, while if the ratios were 1.2-1.4 LA could not be ruled out. Plasma concentrations varied between 8-172 µg/l for DAB, 8-437 µg/l for RIV and 36-178 µg/l for API. LA diagnosis was negative in only eight (27 %) plasma samples from patients treated with DAB, and in five (25 %) and four samples (24 %) from patients treated with RIV and API, respectively. LA Positivity (dRVVT and aPTT ratios >1.4) was found in 5 cases (17 %) among patients treated with DAB, in 10 cases (50 %) treated with RIV and in 7 cases (41 %) treated with API. A concentration-dependent effect of DOACs on dRVVT-based parameters was observed, particularly as regards DAB. At lower concentrations, RIV and API had only minor effects on the confirmatory tests (below 100 µg/l and 70 µg/l, respectively). Our results suggest that a risk of overestimation of LA detection is present in samples from patients treated with DOACs. Therefore, LA testing should not be performed during treatment with DOACs. Prolongation in confirmatory assays may be helpful for the recognition of false positivity, especially as regards DAB.

Whole blood coagulation assays ROTEM and T-TAS to monitor dabigatran treatment.

BACKGROUND: A rapid and reliable assessment of the dabigatran effect is desirable in dabigatran treated patients with uncontrolled bleeding or before acute surgery. OBJECTIVE: To evaluate how the viscoelastic point-of-care test Rotational thromboelastometry (ROTEM) and Total Thrombus-formation system (T-TAS), which studies thrombus formation under flowing conditions, correlate with dabigatran concentrations in patients with atrial fibrillation (AF). METHOD: ROTEM using the reagents In-tem, Ex-tem, Fib-tem or low tissue factor concentration (TF), and T-TAS with the AR-chip (shear rate 600s-1, representing flow in large arteries) were investigated in whole blood samples. Plasma concentrations were determined by mass spectrometry (LC-MS/MS) at trough and post-dose in 30 patients on dabigatran 150mg BID. RESULTS: Median plasma dabigatran concentrations at trough were 86ng/mL (29-150) and post-dose (2.8h after ingestion) 175ng/mL (67-490). The ROTEM clotting time (CT) correlated strongly with dabigatran concentrations when activated with the reagents Ex-tem (r=0.92, p<0.01) and Fib-tem (r=0.93, p<0.01), while with In-tem and low TF the correlation was weaker (r=0.72 and r=0.36, p<0.01). There were significant but weaker correlations also between dabigatran concentrations and T-TAS variables (r-values 0.39-0.41, p<0.01), aPTT (r=0.70, p<0.01) and PT-INR (r=0.43, p<0.01) respectively. CONCLUSIONS: ROTEM Ex-tem and Fib-tem CT shows a strong correlation with dabigatran concentrations in real-life AF-patients, and results are obtained within minutes. This could make ROTEM useful in acute situations. T-TAS detect differences in hemostasis caused by dabigatran, but the relationships to plasma concentrations of dabigatran are weaker than for ROTEM CT with the settings used in this study.

Usefulness of Health Registers for detection of bleeding events in outcome studies.

Administrative and claims databases are attractive for safety studies of anticoagulant and antithrombotic drugs. However, the validity of such data is often uncertain. It was our aim to assess the usefulness of the Swedish administrative health databases for detection of major bleeding events. All individuals with atrial fibrillation in Stockholm County from 2006 to 2013 (n=78,022) were identified from the Swedish Patient register. A search for bleeding diagnoses was done in the Patient register and in the Cause of Death register. The medical records of a random sample of 761 patients were studied and classified in a blinded and pre-specified way. The highest sensitivity (99.5 %) and specificity (94.0 %) were obtained by counting fatal bleeding events with the bleeding diagnosis recorded as first or second cause of death, and all hospitalisations without regard to the position of the diagnosis. Codes for transfusions were unreliable and did not increase accuracy. The registries identified 99.4 % of intracranial bleeding events and 82.6 % of gastrointestinal bleeding events correctly. All patients classified as "no bleedings" were indeed without bleeding. Overall the sensitivity was 85.5 % and the specificity 95.9 % for major bleeding events. In conclusion, Swedish nationwide health registries are well suited for conducting outcome studies involving identification of bleeding events. The use of a diagnostic code for bleeding, irrespective of its position as primary or secondary diagnosis, provided the best sensitivity and specificity for detection of bleeding events, as long as it was limited to contacts resulting in hospital admission.

Benefit of anticoagulation unlikely in patients with atrial fibrillation and a CHA2DS2-VASc score of 1.

BACKGROUND: Patients with atrial fibrillation (AF) and ≥1 point on the stroke risk scheme CHA2DS2-VASc (congestive heart failure, hypertension, age ≥75 years, diabetes mellitus, stroke/transient ischemic attack, vascular disease, age 65-74 years, sex category) are considered at increased risk for future stroke, but the risk associated with a score of 1 differs markedly between studies. OBJECTIVES: The goal of this study was to assess AF-related stroke risk among patients with a score of 1 on the CHA2DS2-VASc. METHODS: We conducted this retrospective study of 140,420 patients with AF in Swedish nationwide health registries on the basis of varying definitions of "stroke events." RESULTS: Using a wide "stroke" diagnosis (including hospital discharge diagnoses of ischemic stroke as well as unspecified stroke, transient ischemic attack, and pulmonary embolism) yielded a 44% higher annual risk than if only ischemic strokes were counted. Including stroke events in conjunction with the index hospitalization for AF doubled the long-term risk beyond the first 4 weeks. For women, annual stroke rates varied between 0.1% and 0.2% depending on which event definition was used; for men, the corresponding rates were 0.5% and 0.7%. CONCLUSIONS: The risk of ischemic stroke in patients with AF and a CHA2DS2-VASc score of 1 seems to be lower than previously reported.

Clinical evaluation of laboratory methods to monitor apixaban treatment in patients with atrial fibrillation.

INTRODUCTION: The direct factor-Xa inhibitor apixaban is approved e.g. for the prevention of stroke in patients with atrial fibrillation (AF). Although routine monitoring of apixaban therapy is currently not recommended, selective monitoring could be useful to optimize efficacy and safety in certain clinical situations. We studied the exposure and effect of apixaban using different laboratory methods in a clinical setting with a well-defined cohort of AF patients. MATERIAL AND METHODS: Seventy AF patients (72±7.4years, 64 % men, mean CHADS2 score 1.7) treated with apixaban 2.5 (n=10) or 5mg BID (n=60). Trough plasma apixaban concentrations determined by liquid chromatography-tandem mass-spectrometry (LC-MS/MS) were compared to the coagulation assays Anti-factor Xa, PT-INR and aPTT. RESULTS: The apixaban plasma concentration determined by LC-MS/MS varied more than 10-fold overall. The range was between 15-83 and 29-186ng/mL for the 2.5mg BID and 5mg BID respectively, with patients receiving 5mg BID having significantly higher apixaban concentrations (p<0.001). A strong correlation between LC-MS/MS and anti-FXa-assay was found (p<0.001), while aPTT and PT-INR were not sensitive enough. There were no significant correlations between gender, creatinine clearance, body weight or age and apixaban exposure. CONCLUSIONS: Anti-FXa-assay performed well upon apixaban concentrations in a normal exposure range. Still LC-MS/MS remains the "gold standard" method, covering also low concentrations. Compared to clinical trials, we observed relatively lower apixaban exposure and a more pronounced difference between high and low dose. Additional information regarding apixaban exposure and benefit-risk profile is needed in order to individualize treatment.

Adherence to warfarin treatment among patients with atrial fibrillation.

BACKGROUND: Treatment with warfarin greatly reduces the risk of stroke related to atrial fibrillation, but will not be effective unless patients adhere to treatment. Lack of fixed dosing makes it difficult to objectively estimate adherence to treatment from prescription data. OBJECTIVE: To evaluate two methods that assess adherence to warfarin from prescription data. DESIGN: Retrospective study of Swedish health care registers. PATIENTS AND METHODS: Age- and sex-specific dose requirements were determined from approx. 1 million blood tests and dosing instructions. By applying these dosages to 163,785 warfarin-treated patients with atrial fibrillation, we calculated the quantity of warfarin that was needed to keep these patients on effective treatment during a mean follow-up of 3.9 years and compared that with the dispensed quantities. The ratio of available drug/time at risk constitutes a measure of adherence on group level. In addition, time intervals between refills were used to assess discontinuation. RESULTS: Both methods showed that 45% of the patients did not have enough warfarin to last 80% of the time at risk. Between 16 and 21% of the patients discontinued within the first year, followed by 8-9% annually during the following years. Patients with high bleeding risk and patients with low embolic risk showed lower endurance. CONCLUSIONS: Adherence to treatment with warfarin can be estimated on group level from prescription data and may be useful for comparison of adherence with warfarin and new oral anticoagulants. When applied to a large warfarin-treated cohort with atrial fibrillation, we found that adherence is low and that measures aiming for improvements are needed .

On the monitoring of dabigatran treatment in "real life" patients with atrial fibrillation.

INTRODUCTION: The oral direct thrombin inhibitor dabigatran is increasingly used to prevent thromboembolic stroke in patients with atrial fibrillation (AF). Routine laboratory monitoring is currently not recommended, but measurements of dabigatran and/or its effect are desirable in certain situations. We studied dabigatran exposure and compared different tests for monitoring of dabigatran in a real-life cohort of AF patients. MATERIAL AND METHODS: Ninety AF patients (68 ± 9 years, 67% men, mean CHADS2 score 1.5) were treated with dabigatran 150 (n=73) or 110 mg BID (n=17). Trough plasma concentrations of total and free dabigatran by liquid chromatography-tandem mass-spectrometry (LC-MS/MS) were compared to indirect measurements by Hemoclot thrombin inhibitors (HTI) and Ecarin clotting assay (ECA), as well as PT-INR and aPTT. RESULTS: Total plasma dabigatran varied 20-fold (12-237 ng/mL with 150 mg BID) and correlated well with free dabigatran (r(2)=0.93). There were strong correlations between LC-MS/MS and HTI or ECA (p<0.001) but these assays were less accurate with dabigatran below 50 ng/mL. The aPTT assay was not dependable and PT-INR not useful at all. There were weak correlations between creatinine clearance (Cockcroft-Gault) and LC-MS/MS, HTI and ECA (p<0.001 for all). A high body weight with normal kidney function was associated with low dabigatran levels. CONCLUSIONS: HTI and ECA reflect the intensity of dabigatran anticoagulation, but LC-MS/MS is required to quantify low levels or infer absence of dabigatran. Most real life patients with a normal creatinine clearance had low dabigatran levels suggesting a low risk of bleeding but possibly limited protection against stroke.

Platelet-derived microparticles during and after acute coronary syndrome.

As microparticles are shedded upon platelet activation, and may be used to assess platelet function, we measured plasma concentrations of platelet-derived microparticles (PMPs) during and after an acute coronary syndrome (ACS). Fifty-one patients with ACS were investigated at admission, within 24 hours (before coronary angiography), and six months later. Sixty-one sex- and age-matched healthy controls were investigated once. PMPs were defined as particles <1.0 µm in size, negative to phalloidin (labels cell-fragments), and positive to CD61. Exposure of phosphatidylserine (PS+), CD62P and CD142 were also measured. Plasma concentrations of PS+PMPs exposing CD61, CD62P and CD142 were elevated 2.5, 6.0-, and 5.0-fold at admission (p<0.001 for all, compared to controls; aspirin only), decreased significantly 24 hours later following initiation of treatment with clopidogrel and subcutaneous anticoagulation (p<0.001 for all), and decreased even further six months later (p<0.01 for all). However, PS+PMPs exposing CD62P or CD142 were still between 1.2-and 2.3-fold higher than in controls (p<0.001 for both). The pattern for PS-PMPs during and after the ACS was very similar to that for PS+PMPs although the numbers were approximately 1/3 lower. In conclusion, PMP concentrations follow the pattern of platelet activation during and after an ACS. Decreased concentrations are observed after initiation of antithrombotic treatment, but PMP exposing CD62P or CD142 are still elevated after six months. Flow cytometric measurements of PMP in frozen-thawed samples enable studies of platelet function in larger clinical trials.

Is fibrin formation and thrombin generation increased during and after an acute coronary syndrome?

INTRODUCTION AND METHODS: In order to study coagulation and fibrinolysis in acute coronary syndrome (ACS) we used a recently developed assay, called OH-index, which provides simultaneous measurements of fibrin formation and fibrinolysis (fibrin degradation) in the patients' plasma. We also investigated thrombin generation using the calibrated automated thrombogram (CAT), and assessed thrombin generation in vivo by measuring F1+2 plasma concentrations. In addition, to better characterize the patients we also assessed markers of inflammation and endothelial function. Eighty-seven ACS patients were sampled at admission, within 24 hours during treatment with low molecular weight heparin (LMH), and 6 months later; 65 healthy controls were also sampled. RESULTS: As assessed by OH-index fibrin formation was slightly depressed at admission, profoundly depressed during LMH treatment and comparable to controls at 6 months, whereas fibrin degradation was elevated, particularly during LMH treatment. F1+2 levels decreased during LMH treatment but did not deviate significantly from controls at admission or in convalescence. CAT data showed that peak thrombin was higher at admission and after 6 months compared to controls, whereas the endogenous thrombin potential only tended to be elevated. Both variables were strongly reduced during LMH treatment. Patients had elevated levels of markers of inflammation and endothelial function as expected. CONCLUSION: ACS-patients have an increased capacity to generate thrombin and an enhanced capacity to degrade fibrin in the acute phase. Increased thrombin generation persists also 6 months after the event.

ADAMTS13 and von Willebrand factor concentrations in patients with diabetes mellitus.

The von Willebrand factor (VWF) is elevated in patients with diabetes mellitus and degraded by a metalloprotease, ADAMTS13. We hypothesized that this elevation is due to a decreased function of ADAMTS13. Thus, we investigated ADAMTS13 in patients with diabetes mellitus without and with peripheral artery occlusive disease (PAOD). When treating the latter group with dalteparin, VWF is reported to increase significantly, and we therefore measured ADAMTS13 also in these patients. VWF antigen and ADAMTS13 antigen and activity concentrations were measured in patients with diabetes mellitus but without PAOD (diabetes mellitus; n = 23) and with diabetes mellitus and PAOD (diabetes mellitus + PAOD; n = 65) before and after treatment with dalteparin or placebo. In the diabetes mellitus group, concentration of VWF antigen was significantly higher, whereas that of ADAMTS13 activity was significantly lower than in the healthy controls. In the diabetes mellitus along with PAOD group, VWF antigen was significantly higher, but ADAMTS13 antigen or activity did not differ significantly from those of healthy controls. The ADAMTS13 activity/antigen ratio was lower than in controls only in the diabetes mellitus patient group. VWF antigen increased significantly during dalteraprin treatment, whereas ADAMTS13 activity and antigen remained unchanged. Only patients with diabetes mellitus had significantly lower concentrations of ADAMTS13 activity in plasma than controls, although the diabetes mellitus along with PAOD had a more pronounced VWF antigen elevation than diabetes mellitus patients, illustrating a possible link between ADAMTS13 and microangiopathy in diabetes mellitus patients. The increase in VWF antigen concentration during treatment with dalteparin does not seem to be due to changes in ADAMTS13.

Can both EDTA and citrate plasma samples be used in measurements of fibrinogen and C-reactive protein concentrations?

BACKGROUND: Fibrinogen and C-reactive protein (CRP) concentrations are predictors of outcome in the atherosclerotic patient. It is important in risk stratification that these quantities are measured reproducibly in routine and research. METHOD: In the present study, we compare measurements of fibrinogen and high-sensitivity CRP in EDTA and citrate plasma samples (n=150) using nephelometric immunoassays. Fibrinogen was also measured in citrate plasma using a clotting method. RESULTS: In approximately one-third of the samples, the fibrinogen concentration measured by immunoassay was higher in citrate plasma than in EDTA plasma, in spite of the dilution by citrate. The immunoassay results of fibrinogen concentration measurements in EDTA and citrate plasma differed significantly and also differed from those of functionally measured fibrinogen concentrations. A difference was found between the concentration of CRP in EDTA plasma and citrated plasma which also did not correspond to the dilution. CONCLUSIONS: Reproducibility of results is essential in risk stratification by fibrinogen or high-sensitivity CRP concentrations and small differences close to the decision limits may have a decisive impact. Immunological measurements are liable to confounding effects that may be difficult to foresee, qualitatively and quantitatively. Great care should be observed when measuring the concentration of calcium containing analytes in anticoagulated samples. Fibrinogen concentrations should preferably be measured functionally in citrate plasma.