Shortened activated partial thromboplastin time, a hemostatic marker for hypercoagulable state during acute coronary event

Brief communication: coagulation profiles of HIV positive patients on antiretroviral therapy (ART) at the Mampong Municipal Hospital, Ashanti-Region, Ghana: a case control study

This study aimed to ascertain how the current two ART regimens used in Ghana affected HIV patients' coagulation profiles. A case-control study was conducted on 102 HIV positive patients at the Mampong Municipal Hospital. Coagulation parameters measured showed APTT was normal in majority of ART-experienced participants but prolonged in majority of ART-naïve participants. The mean platelet count was significantly higher in ART-experienced participants. No significant differences were found between the coagulation profiles of ART-experienced patients on two different drug regimens. In conclusion, current ART can enhance the coagulation profiles in HIV-infected patients, by improving platelet count and APTT.

Activated partial thromboplastin time-based clot waveform analysis: a potential for application in acute myocardial infarction and its complications

Activated partial thromboplastin time (aPTT)-based clot waveform analysis (CWA) is a plasma-based global haemostatic assay. Elevated CWA parameters have been associated with hypercoagulability in venous thromboembolism, but its role in arterial thrombotic disease is uncertain. This study aims to explore the relationship between aPTT-based CWA and acute myocardial infarction (AMI) and its complications. In a retrospective cohort study of patients with AMI who underwent emergency cardiac catheterisation, pre-procedural aPTT and CWA parameters-min1, min2 and max2 were measured. These were compared against a control group of patients, consisting of patients who underwent elective orthopaedic and urological procedures. Within the AMI cohort, we also compared aPTT and CWA parameters of those with and without clinical complications of AMI. Results: Compared to controls (N = 109), patients with AMI (N = 214) had shorter aPTT (26.7 ± 3.3 s vs 27.9 ± 1.7 s, P < 0.001) and higher CWA parameters (min1: 6.11 ± 1.40%/s vs 5.58 ± 1.14%/s; min2: 0.98 ± 0.23%/s2 vs 0.90 ± 0.19%/s2; max2: 0.81 ± 0.20%/s2 vs 0.74 ± 0.16%/s2, all P ≤ 0.001). There was an increased incidence of elevated CWA parameters, in the AMI group, with odds ratio (OR) of 2.06 [95% CI 1.10-3.86], 2.23 (95% CI 1.18-4.24) and 2.01 (95% CI 1.07-3.77) for min1, min2 and max2, respectively. Similarly, elevated min1 and min2 were both individually associated with the presence of adverse outcomes of AMI, both with ORs of 2.63 (95% CI 1.24-5.59). Elevated aPTT-based CWA parameters are significantly associated with the occurrence of AMI and its complications. These findings identify the potential utility of CWA as risk and prognostic markers for AMI and warrants future works.

Reference interval for the C-ACT activated clotting time test in healthy dogs using a water bath and manual assessment of clot formation

AIMS

To establish a reference range for the canine C-ACT activated clotting time (ACT) test using a water bath and visual clot assessment technique.

METHODS

Healthy, privately owned dogs (n = 48) were prospectively recruited to the study. Blood samples were collected via direct jugular venipuncture for complete blood count, serum biochemistry, prothrombin time (PT) and activated partial thromboplastin time (aPTT). Five animals with major abnormalities or who became agitated during phlebotomy were excluded. For the 43 remaining animals, 2 mL of blood was then collected via the cephalic vein and added directly to a C-ACT tube that was shaken vigorously before being placed in a water bath at 37°C. Tubes were visually assessed for clot formation and C-ACT was recorded in seconds when the magnet within the tube lodged in the clot.

RESULTS

Forty-three animals were eligible for inclusion. The nonparametric reference interval (capturing the central 95% of the data) was 50-80 seconds, with a 90% CI for the lower limit of 50-55 seconds and a 90% CI for the upper limit of 75-80 seconds. The C-ACT ACT test had a positive correlation with aPTT (0.42, 95% CI = 0.13-0.64). There was no evidence of a correlation between C-ACT ACT and age, weight, PT, haematocrit, white blood cell count, platelet count or total protein.

CONCLUSIONS AND CLINICAL RELEVANCE

The results of this study suggest that the normal reference interval for ACT in dogs using C-ACT tubes in a 37°C water bath is 50-80 seconds. Care should be taken extrapolating the results of this study to the general population, as the smaller study design had less control for confounders than a larger study. However, when using the described analytical methods, C-ACT tube ACT test results > 80 seconds should be considered prolonged in dogs and should prompt further investigation.

ABBREVIATIONS

ACT: Activated clotting time; aPTT: Activated partial thromboplastin time; EDTA: Ethylenediaminetetraacetic acid; Hct: Haematocrit; PT: Prothrombin time.

Juvenile patients with the homozygous MTHFR C677T genotype develop ischemic stroke 5 years earlier than wild type

To compare age at 1st ischaemic stroke (IS) in a cohort of juvenile (< 46 years of age) IS patients evaluated for the rs1801133 polymorphism (C → T677) of the methylene tetrahydrofolate reductase (MTHFR) gene; to identify predictors of age at IS and of type of cerebral vessel involvement, small vessel disease (SVD) vs large vessel disease (LVD) responsible for the IS; to evaluate possible associations between other clinical and laboratory variables. Retrospective cohort study on 82 MTHFR TT, 54 MTHFR TC and 34 MTHFR CC participants; data regarding age, sex, age at IS, history of dyslipidaemia, hypertension, smoking, migraine and homocysteine (HC) as well as neuroimaging were collected. Age at IS was lower in MTHFR TT than MTHFR TC and CC (35 ± 4 vs 38 ± 0 vs 40 ± 3 years, respectively, p = 0.002); plasma HC (median, interquartile range) was higher in MTHFR TT than in the other groups [16.7 (11.8, 28.6) vs 11.4 (8.2, 16.1) vs 9.8 (7.9, 1.3) respectively, p < 0.0001)] and was higher in SVD than LVD [17.4 (12.4, 32.5) vs  11.4 (8.8, 16.4) p < 0.0001]. MTHFR TT independently predicted age at IS (p = 0.0008) alongside smoking both as a categorical (p = 0.003) or continuous variable (p = 0.02), whereas HC independently predicted SVD as categorical (p = 0.01) and continuous variable (p < 0.0001). Smoking positively predicted plasma HC (p = 0.005) and negatively the activated partial thromboplastin ratio (aPTTr) (p = 0.02). Juvenile IS carriers of the MTHFR TT genotype develop their 1st occlusion on average 5 years earlier compared to the CC genotype; smoking contributes to this prematurity adversely affecting plasma HC and coagulation whereas plasma HC predicts IS secondary to SVD. Public health campaigns against smoking should highlight the prematurity of IS in the juvenile population.

Magnitude of Coagulation Abnormalities and Associated Factors Among Patients with Heart Diseases at the University of Gondar Comprehensive Specialized Hospital

Background

Heart disease is a leading cause of hospitalization, death, and poor physical function due to comorbid conditions such as atrial fibrillation and stroke. It affects the blood hemostatic system, vasculature, and flow dynamics, causing both arterial and venous thrombosis. Thus, this study aimed to determine the magnitude of coagulation abnormalities among patients with heart disease attending the University of Gondar Comprehensive Specialized hospital.

Methods

A cross-sectional study was conducted on a total of 98 patients with heart disease. Pretested structured questionnaires were used to collect data on socio-demographic and clinical variables. About 6 mL of venous blood was collected with the vacutainer method and analyzed using Huma cue-due plus and Sysmex KX-21N hematology analyzers for assessing coagulation abnormalities. Stool samples were processed via a direct wet mount. Thin and thick blood films were examined to assess malaria parasites. Data was entered into EPI-Info version 3.5.3 and then transported to SPSS version 20 for analysis. Descriptive statistics were summarized using frequency and percentage. Univariate and multivariate logistic regression models were fitted to identify factors associated with coagulopathy. P-value <0.05 was considered to be statistically significant.

Results

The overall magnitude of coagulation abnormalities (thrombocytopenia, prolonged prothrombin time, and activated partial thromboplastin time) in patients with heart diseases was 85.7% (95% CI: 81.96, 89.45). Besides, prolonged prothrombin time, prolonged activated partial thromboplastin time, and thrombocytopenia were detected in 83.7%, 33.7%, and 12.2% of the study participants, respectively. Participants who are taking medications for chronic disease (AOR = 0.17; 95% CI: 0.04, 0.69), participants with stroke (AOR = 20; 95% CI: 14.7, 35), and participants taking antibiotics (AOR = 8.17; 95% CI: 1.66, 40.27) were significantly associated with prolonged coagulation time.

Conclusion

This study showed that patients with heart disease had prolonged prothrombin time, activated partial thromboplastin time, and thrombocytopenia. Therefore, coagulation parameters are required to be checked regularly to monitor coagulation disorders and their complications in heart disease patients.

Therapeutic Effects of Modified Si-Miao-Yong-An Decoction in the Treatment of Rat Myocardial Ischemia/Reperfusion Injury

Objective

Modified Si-Miao-Yong-An decoction (MSMYA) was empirically originated from Si-Miao-Yong-An Decoction, which has been utilized for centuries to treat vasculopathy as well as heart diseases through clearing heat and detoxifying. This study aimed at confirming MSMYA's therapeutic effects for treating myocardial ischemia/reperfusion (I/R) injury and its underlying mechanisms.

Methods

Rats were intragastrically administered with MSMYA for 4 weeks after ischemia/reperfusion (I/R) operation. Superoxide dismutase (SOD) and malondialdehyde (MDA) concentration were determined by calorimetry. Coagulation function was determined using an automated coagulation analyzer. Levels of cysteinyl aspartate specific proteinase (caspase)-1, interleukin (IL)-1β, interleukin (IL)-18, and lactate dehydrogenase (LDH) were measured by an enzyme-linked immunosorbent assay (ELISA). Infarct size was determined by triphenyltetrazolium chloride (TTC) staining. Myocardial histopathological and ultrastructure changes were examined by H&E staining and electron microscopy, respectively. Relative mRNA expression of NLRP3, an apoptosis-associated speck-like proteins containing the caspase activation and recruitment domain (ASC), caspase-1, IL-1β, and IL-18 were analyzed using quantitative real-time polymerase chain reaction (PCR). Meanwhile, their relative protein expressions were measured using western blotting.

Results

The results showed MSMYA can inhibit oxidative stress by increasing SOD and reducing MDA, suppress inflammatory reaction by decreasing NLRP3 inflammasome-related cytokines' level, improve coagulation function by increasing prothrombin time (PT) and activating partial thromboplastin time (APTT), and ameliorate myocardial histopathological and ultrastructural changes. In addition, MSMYA's cardioprotective effects probably related to suppressing NLRP3 inflammasome pathway activation by reducing NLRP3 inflammasome molecular mRNA and protein relative expression.

Conclusion

The results indicated that MSMYA played an important role in protecting the myocardium from I/R injury. The likely mechanism is the inhibition of oxidative stress, improvement of cardiac injury, and the reduction of NLRP3-related inflammatory cytokines release. This provides a basis for further research on the mechanism and clinical application of MSMYA to improve myocardial I/R injury.

Coeliac artery and splenic artery thrombosis complicated with splenic infarction 7 days following the first dose of Oxford vaccination, causal relationship or coincidence?

The novel coronavirus SARS-CoV-2 became a global pandemic in late 2019, and is still ongoing in 2021 causing significant morbidity and mortality. The advent of vaccinations heralded the turning of the tide. The Oxford jab, a vector-based vaccine was favoured due to its low cost and ease of storage. However, its potential association with thromboembolic adverse events resulted in controversy and disrupted its roll-out and use. The aetiopathogenesis of these thromboembolic events and its association with the Oxford vaccine are still speculative and uncertain, more so in the background of SARS-CoV-2 infection being highly thrombogenic in its own right. This paper presents a case of an otherwise healthy 50-year-old Caucasian man who developed acute abdominal pain 7 days following the first dose of Oxford vaccine and was found to have coeliac and splenic artery thrombosis complicated with splenic infarction.

Evaluation of Blood Coagulation Parameters and ADMA, NO, IL-6, and IL-18 Serum Levels in Patients with Neovascular AMD before, during, and after the Initial Loading Phase of Intravitreal Aflibercept

We evaluated the effect of intravitreal injections of aflibercept (IVA) on blood coagulation parameters including prothrombin time (PT), activated partial thromboplastin time (APTT), and thrombin time (TT), as well as asymmetric dimethylarginine (ADMA), nitric oxide (NO), interleukin 6 (IL-6), and interleukin 18 (IL-18) serum levels in patients with neovascular AMD (nAMD). Twenty-two eyes of 22 patients with nAMD were included. Parameters were evaluated before and 2–3 days after the first IVA injection, and then immediately before and 2–3 days after the third IVA injection. We revealed prolongation of the TT after the initial loading phase of IVA (p = 0.041) and a significant increase in IL-18 serum concentration immediately before the third IVA administration compared to baseline (p = 0.037). There were no statistically significant differences of other parameters and PT, APTT, ADMA, NO, and IL-6 values remained within the normal range at each of the time points of the study. Our results suggest that repeated IVA administration may affect the common blood coagulation pathway, which manifests as a prolongation of the TT value. Furthermore, we showed a significant increase in serum concentration of the pro-inflammatory cytokineIL-18during the initial loading phase of IVA.

Procoagulatory changes induced by head-up tilt test in patients with syncope: observational study

Background

Orthostatic hypercoagulability is proposed as a mechanism promoting cardiovascular and thromboembolic events after awakening and during prolonged orthostasis.

We evaluated early changes in coagulation biomarkers induced by tilt testing among patients investigated for suspected syncope, aiming to test the hypothesis that orthostatic challenge evokes procoagulatory changes to a different degree according to diagnosis.

Methods

One-hundred-and-seventy-eight consecutive patients (age, 51 ± 21 years; 46% men) were analysed. Blood samples were collected during supine rest and after 3 min of 70° head-up tilt test (HUT) for determination of fibrinogen, von Willebrand factor antigen (VWF:Ag) and activity (VWF:GP1bA), factor VIII (FVIII:C), lupus anticoagulant (LA1), functional APC-resistance, and activated prothrombin time (APTT) with and without activated protein C (C+/−). Analyses were stratified according to age, sex and diagnosis.

Results

After 3 min in the upright position, VWF:Ag (1.28 ± 0.55 vs. 1.22 ± 0.54; p < 0.001) and fibrinogen (2.84 ± 0.60 vs. 2.75 ± 0.60, p < 0.001) increased, whereas APTT/C+/− (75.1 ± 18.8 vs. 84.3 ± 19.6 s; p < 0.001, and 30.8 ± 3.7 vs. 32.1 ± 3.8 s; p < 0.001, respectively) and APC-resistance (2.42 ± 0.43 vs. 2.60 ± 0.41, p < 0.001) decreased compared with supine values. Significant changes in fibrinogen were restricted to women (p < 0.001) who also had lower LA1 during HUT (p = 0.007), indicating increased coagulability. Diagnosis vasovagal syncope was associated with less increase in VWF:Ag during HUT compared to other diagnoses (0.01 ± 0.16 vs. 0.09 ± 0.17; p = 0.004).

Conclusions

Procoagulatory changes in haemostatic plasma components are observed early during orthostasis in patients with history of syncope, irrespective of syncope aetiology. These findings may contribute to the understanding of orthostatic hypercoagulability and chronobiology of cardiovascular disease.

Opposite effects of Agrimonia pilosa Ledeb aqueous extracts on blood coagulation function

BACKGROUND

Agrimonia pilosa Ledeb (APL) has showed anticoagulant and antithrombotic activities in some studies, whereas its actual effects on blood coagulation are still unclear. This study was designed to observe the in vitro effects of APL aqueous extracts on blood coagulation, as well as to investigate the underlying mechanisms.

METHODS

Studies were divided into four groups: 0, 4, 20, and 80 g/L of APL aqueous extracts mixed with plasma or whole blood samples. Clotting time of whole blood, plasma coagulation tests, activities of plasma coagulation factors, plasma calcium ion, platelet aggregation test, and platelet fibrinogen receptor as well as the blood viscosity were measured.

RESULTS

It was observed that the APL aqueous extracts in 4 g/L significantly prolonged the whole blood clotting time and activated partial thromboplastin time, shortened prothrombin time, decreased activities of coagulation factor VIII, IX and XI, and levels of platelet aggregation and fibrinogen receptor expression. However, coagulation factor VII activity, and blood viscosity were increased after the extracts treatment. And the effects of APL extracts were in a concentration-dependent manner (0-80 g/L).

CONCLUSIONS

The results suggest that APL aqueous extracts have a total anticoagulant activity, whereas they exhibit opposite effects of greater anticoagulant activity than pro-coagulant activity.

Evaluation of Potential Clinical Surrogate Markers of a Trauma Induced Alteration of Clotting Factor Activities

Objective. The aim of this study was to identify routinely available clinical surrogate markers for potential clotting factor alterations following multiple trauma. Methods. In 68 patients admitted directly from the scene of the accident, all soluble clotting factors were analyzed and clinical data was collected prospectively. Ten healthy subjects served as control group. Results. Patients showed reduced activities of clotting factors II, V, VII, and X and calcium levels (all P < 0.0001 to 0.01). Levels of hemoglobin and base deficit correlated moderately to highly with the activities of a number of clotting factors. Nonsurvivors and patients who needed preclinical intubation or hemostatic therapy showed significantly reduced factor activities at admission. In contrast, factor VIII activity was markedly elevated after injury in general (P < 0.0001), but reduced in nonsurvivors (P < 0.05). Conclusions. Multiple trauma causes an early reduction of the activities of nearly all soluble clotting factors in general. Initial hemoglobin and, with certain qualifications, base deficit levels demonstrated a potential value in detecting those underlying clotting factor deficiencies. Nevertheless, their role as triggers of a hemostatic therapy as well as the observed response of factor VIII to multiple trauma and also its potential prognostic value needs further evaluation.

Retrospective evaluation of shortened prothrombin time or activated partial thromboplastin time for the diagnosis of hypercoagulability in dogs: 25 cases (2006-2011)

OBJECTIVE

To evaluate the relationship between shortened prothrombin time (PT) or activated partial thromboplastin time (aPTT) values, clinical findings associated with hypercoagulability, suspicion of pulmonary thromboembolism (PTE), D-dimer concentrations, and thromboelastogram (TEG) indices.

DESIGN

Retrospective observational study from 2006 to 2011.

SETTING

University veterinary teaching hospital.

ANIMALS

Twenty-three dogs with TEG tracings and shortened PT or aPTT values and 23 control dogs with TEG tracings and normal PT and aPTT values.

MEASUREMENTS AND MAIN RESULTS

Parameters evaluated included signalment, coagulation testing results (PT, aPTT, D-dimer concentration), TEG measurements (R, K, α, maximal amplitude) and calculated clotting index, findings of clinical hypercoagulability (thrombosis of intravenous/intra-arterial catheters, vessel thrombosis, and suspected PTE). Dogs with shortened PT or aPTT had significantly more thrombus formation (P = 0.038), suspicion of PTE (P < 0.001), and increased D-dimer concentration (P < 0.001) compared to dogs with normal PT and aPTT values. There were no significant findings when compared to TEG values.

CONCLUSIONS

A shortened PT or aPTT in dogs may be indicative of a hypercoagulable state as evidenced by an increased incidence of thrombosis, frequency of suspected PTE, and increased circulating D-dimers. A prospective study is warranted to further evaluate the use of PT and aPTT to diagnose hypercoagulable states.

Mutagenicity and preclinical safety assessment of the aqueous extract of Clinacanthus nutans leaves

CONTEXT

Clinacanthus nutans (CN) is used traditionally for treating various illnesses. Robust safety data to support its use is lacking.

OBJECTIVE

To evaluate the adverse effects of aqueous extract of CN leaves (AECNL).

MATERIALS AND METHODS

The oral toxicity of the AECNL was tested following Organisation for Economic Co-operation and Development (OECD) guidelines. Mutagenicity (Ames test) of AECNL was evaluated using TA98 and TA100 Salmonella typhimurium strains.

RESULTS

No mortality or morbidity was found in the animals upon single and repeated dose administration. However, significant body weight loss was observed at 2000 mg/kg during sub-chronic (90 d) exposure. In addition, increased eosinophil at 500 mg/kg and decreased serum alkaline phosphatase levels at 2000 mg/kg were observed in male rats. Variations in glucose and lipid profiles in treated groups were also observed compared to control. Ames test revealed no evidence of mutagenic or carcinogenic effects at 500 μg/well of AECNL.

CONCLUSION

The median lethal dose (LD50) of the AECNL is >5000 mg/kg and the no-observed-adverse-effect level is identified to be greater than 2000 mg/kg/day in 90-d study.

Elevated Factor VIII Levels and Shortened APTT in Recurrent Abortions

INTRODUCTION

Thrombotic disorders have been found to be associated with recurrent abortions. Several risk factors have been identified. APTT reflects the common pathway and intrinsic pathway of coagulation cascade and hence is a good marker for thrombotic work. Elevated factor VIII: C has also been identified as risk factor for recurrent miscarriage. This study aims at identifying association of elevated factor VIII levels, shortened APTT and recurrent abortions in Indian population as little has been studied about this and the literature available is also based on studies done in European population. This study also aims to find whether shortened APTT can be an independent risk as well.

MATERIALS AND METHODS

Women referred to the obstetrics department with a history of early recurrent early pregnancy loss (at least three pregnancy losses before 13 weeks of gestation) were included in this study. Exclusion criteria were elevated CRP levels, positive antiphospholipid antibodies, endocrine, immunological or anatomical cause of embryo demise. A total of 68 cases of recurrent abortion were included in this study, 68 normal pregnant females (<15 weeks of gestation) were also included as controls with no history of abortion. The age group of the cases as well as control was 20-45 years. Activated partial thromboplastin time and factor VIII assay (one stage APTT based) were done on the blood samples.

RESULTS

Increased factor VIII levels were seen in 25 cases (36.4%); 19 cases showed shortened APTT (27.3%); 12 cases showed both increased factor VIII levels as well as shortened APTT (18%). All risk factors were negative in 36 cases (52.9%). None of the controls showed elevated factor VIII levels or shortened APTT. The mean APTT values of the control subjects was 31.01 and cases were 27.01 (p=0.001). The mean factor VIII levels of case were 152.85% and control 144.953% (p=0.012).

CONCLUSION

There was significant association between recurrent abortions and elevated factor VIII :c levels and shortened APTT. Shortened APTT was also identified as an independent risk factor.

Targeting blood thrombogenicity precipitates atherothrombotic events in a mouse model of plaque destabilization

Although some features of plaque instability can be observed in genetically modified mouse models, atherothrombosis induction in mice has been attested to be difficult. We sought to test the hypothesis that alterations in blood thrombogenicity might have an essential role in the development of atherothrombosis in ApoE-/- mice. In a mouse model of plaque destabilization established in our laboratory, we targeted blood thrombogenicity by systemically overexpressing murine prothrombin via adenovirus-mediated gene transfer. Systemic overexpression of prothrombin increased blood thrombogenicity, and remarkably, precipitated atherothrombotic events in 70% of the animals. The affected plaques displayed features of culprit lesions as seen in human coronary arteries, including fibrous cap disruption, luminal thrombosis, and plaque hemorrhage. Treatment with aspirin and clopidogrel substantially reduced the incidence of atherothrombosis in this model. Mechanistically, increased inflammation, apoptosis and upregulation of metalloproteinases contributed to the development of plaque destabilization and atherothrombosis. As conclusions, targeting blood thrombogenicity in mice can faithfully reproduce the process of atherothrombosis as occurring in human coronary vessels. Our results suggest that blood-plaque interactions are critical in the development of atherothrombosis in mice, substantiating the argument that changes in blood coagulation status may have a determinant role in the onset of acute coronary syndrome.

Reversing targeted oral anticoagulants

Dabigatran, rivaroxaban, and apixaban are orally active anticoagulants that are approved in many countries. Dabigatran inhibits thrombin, whereas rivaroxaban and apixaban are factor Xa inhibitors. In clinical trials, these novel oral anticoagulants were at least as effective as warfarin for preventing stroke in patients with atrial fibrillation, but with a lower rate of serious bleeding. However, the lack of true antidotes for these agents has caused concern when patients suffer life-threatening bleeding or trauma or require emergent invasive procedures. True antidotes are under development for all of these agents. In the meantime, activated and nonactivated prothrombin complex concentrates have been used as reversal agents. Factor VIIa may also be effective for reversal of the factor Xa inhibitors. Reversal of novel oral anticoagulants by these hemostatic agents has not been studied in bleeding human patients, so their true efficacy and appropriate dosing are not known.

A gene-centric analysis of activated partial thromboplastin time and activated protein C resistance using the HumanCVD focused genotyping array

Activated partial thromboplastin time (aPTT) is an important routine measure of intrinsic blood coagulation. Addition of activated protein C (APC) to the aPTT test to produce a ratio, provides one measure of APC resistance. The associations of some genetic mutations (eg, factor V Leiden) with these measures are established, but associations of other genetic variations remain to be established. The objective of this work was to test for association between genetic variants and blood coagulation using a high-density genotyping array. Genetic association with aPTT and APC resistance was analysed using a focused genotyping array that tests approximately 50 000 single-nucleotide polymorphisms (SNPs) in nearly 2000 cardiovascular candidate genes, including coagulation pathway genes. Analyses were conducted on 2544 European origin women from the British Women's Heart and Health Study. We confirm associations with aPTT at the coagulation factor XII (F12)/G protein-coupled receptor kinase 6 (GRK6) and kininogen 1 (KNG1)/histidine-rich glycoprotein (HRG) loci, and identify novel SNPs at the ABO locus and novel locus kallikrein B (KLKB1)/F11. In addition, we confirm association between APC resistance and factor V Leiden mutation, and identify novel SNP associations with APC resistance in the HRG and F5/solute carrier family 19 member 2 (SLC19A2) regions. In conclusion, variation at several genetic loci influences intrinsic blood coagulation as measured by both aPTT and APC resistance.