Increased levels of free thyroxine and risk of venous thrombosis in a large population-based prospective study

Pathophysiology, diagnosis and management of cerebral venous thrombosis: A comprehensive review

Cerebral venous thrombosis is a rare cause of stroke in young mostly female adults which is frequently overlooked due to its variable clinical and radiological presentation. This review summarizes current knowledge on it risk factors, management and outcome in adults and highlights areas for future research. Females are 3 times more commonly affected and are significantly younger than males. The presenting symptoms can range from headache to loss of consciousness. However, the often-nebulous nature of symptoms can make the diagnosis challenging. Magnetic resonance imaging with venography is often the diagnostic imaging of choice. While unfractionated or low molecular-weight heparin is the mainstay of treatment, endovascular intervention with thrombolysis or thrombectomy and decompressive craniectomy may be required depending on clinical status. Nevertheless, approximately 80% of patients have a good recovery but mortality rates of -5% to 10% are not uncommon. Diagnosing cerebral venous thrombosis can be challenging but with vigilance and expert care patients have the best chance of a good clinical outcome.

Frequency of Thrombotic Risk Factors in Patients with Chronic Thromboembolic Pulmonary Hypertension and Acute Pulmonary Embolism: A Case-Control Study

Chronic thromboembolic pulmonary hypertension (CTEPH) is a serious complication of acute pulmonary embolism (PE) which remains underdiagnosed. A better understanding of risk factors for CTEPH would improve our ability to predict which PE survivors are at risk. Several medical conditions-including malignancy, splenectomy, thyroid hormone supplementation, the presence of an intravascular device, inflammatory bowel disease, osteomyelitis, and non-O blood group-have been associated with increased risk of CTEPH, primarily in studies comparing patients with CTEPH to individuals with non-thrombotic conditions. Because many of these conditions increase thrombosis risk, it remains unclear whether their association with CTEPH reflects a general effect on thrombosis risk, or a specific effect on the risk of developing CTEPH as an outcome of thrombosis. We performed a case-control study comparing the frequencies of these conditions in patients with CTEPH versus patients with acute PE who did not develop CTEPH. The conditions studied were equally frequent in the CTEPH and PE cohorts, although there was a trend towards an increased frequency of splenectomy and non-O blood group among the CTEPH cohort. Thus, other than the possible exceptions of splenectomy and non-O blood group, the investigated medical conditions do not appear likely to increase the risk of CTEPH as an outcome of acute PE, and thus are unlikely to be useful in predicting CTEPH risk among PE survivors.

Effects of Thyroid Function on Hemostasis, Coagulation, and Fibrinolysis: A Mendelian Randomization Study

Background: Untreated hypothyroidism is associated with acquired von Willebrand syndrome, and hyperthyroidism is associated with increased thrombosis risk. However, the causal effects of thyroid function on hemostasis, coagulation, and fibrinolysis are unknown. Methods: In a two-sample Mendelian randomization (MR) study with genome-wide association variants, we assessed causality of genetically predicted hypothyroidism (N = 134,641), normal-range thyrotropin (TSH; N = 54,288) and free thyroxine (fT4) (N = 49,269), hyperthyroidism (N = 51,823), and thyroid peroxidase antibody positivity (N = 25,821) on coagulation (activated partial thromboplastin time, von Willebrand factor [VWF], factor VIII [FVIII], prothrombin time, factor VII, fibrinogen) and fibrinolysis (D-dimer, tissue plasminogen activator [TPA], plasminogen activator inhibitor-1) from the CHARGE Hemostasis Consortium (N = 2583-120,246). Inverse-variance-weighted random effects were the main MR analysis followed by sensitivity analyses. Two-sided p < 0.05 was nominally significant, and p < 0.0011[ = 0.05/(5 exposures × 9 outcomes)] was Bonferroni significant for the main MR analysis. Results: Genetically increased TSH was associated with decreased VWF [β(SE) = -0.020(0.006), p = 0.001] and with decreased fibrinogen [β(SE) = -0.008(0.002), p = 0.001]. Genetically increased fT4 was associated with increased VWF [β(SE) = 0.028(0.011), p = 0.012]. Genetically predicted hyperthyroidism was associated with increased VWF [β(SE) = 0.012(0.004), p = 0.006] and increased FVIII [β(SE) = 0.013(0.005), p = 0.007]. Genetically predicted hypothyroidism and hyperthyroidism were associated with decreased TPA [β(SE) = -0.009(0.024), p = 0.024] and increased TPA [β(SE) = 0.022(0.008), p = 0.008], respectively. MR sensitivity analyses showed similar direction but lower precision. Other coagulation and fibrinolytic factors were inconclusive. Conclusions: In the largest genetic studies currently available, genetically increased TSH and fT4 may be associated with decreased and increased synthesis of VWF, respectively. Since Bonferroni correction may be too conservative given the correlation between the analyzed traits, we cannot reject nominal associations of thyroid traits with coagulation or fibrinolytic factors.

The interrelationship between pregnancy, venous thromboembolism, and thyroid disease: a hypothesis-generating review

Pregnancy induces physiological changes that affect the risk of thrombosis and thyroid disease. In this hypothesis-generating review, the physiological changes in the coagulation system and in thyroid function during a normal pregnancy are described, and the incidence of venous thromboembolism (VTE) and thyroid disease in and after a pregnancy are compared and discussed. Furthermore, evidence regarding the association between thyroid disease and VTE in non-pregnant individuals is scrutinized. In conclusion, a normal pregnancy entails hormonal changes, which influence the onset of VTE and thyroid disease. Current evidence suggests an association between thyroid disease and VTE in non-pregnant individuals. This review proposes the hypothesis that maternal thyroid disease associates with VTE in pregnant women and call for future research studies on this subject. If an association exists in pregnant women specifically, such findings may have clinical implications regarding strategies for thyroid function testing and potential thromboprophylaxis in selected individuals.

Preoperative Potassium Iodide Treatment in Patients Undergoing Thyroidectomy for Graves' Disease-Perspective of a European High-Volume Center

BACKGROUND

Potassium iodide (KI) treatment affects the vascularity of the thyroid gland and therefore may improve intraoperative visualization of essential structures. However, clear evidence for its usage is lacking, and its implementation in patients suffering from Graves' disease is becoming rare. The objective of this retrospective study was to assess the impact of KI treatment on the intraoperative course and the outcome of patients undergoing thyroidectomy for Graves' diseases.

METHODS

The study included 442 patients: 125 patients (28.3%) who received a preoperative treatment with KI ("Group KI") and 317 patients (71.7%) without a KI therapy ("Group No-KI"). Indication for KI treatment was a thyroid bruit (82.5%), as well as hyperthyroidism refractive to medical treatment with antithyroid drugs (17.4%).

RESULTS

All patients underwent total thyroidectomy. Permanent vocal cord paresis and permanent hypoparathyroidism were similar in both groups. KI treatment was associated with a significantly longer operative time (142 vs. 128 min, p < 0.001) and a significant higher weight of the thyroid gland. KI treatment did not impact duration of hospital stay or occurrence of secondary hemorrhage.

CONCLUSIONS

The complication rate of this study population with clinically severe GD was very low-which may be caused by pre-treatment of patients. The complementary option of a potassium iodide treatment before surgery remains a possibility and should be implemented individually.

Rise of levels of von Willebrand factor and factor VIII with age: Role of genetic and acquired risk factors

BACKGROUND

Von Willebrand factor (VWF) levels are regulated by genetic and acquired factors. The acquired factors are mostly related to age and could be mediators of the age effect on VWF levels.

OBJECTIVES

To disentangle the role of genetic (sex, blood group) and acquired factors (comorbidities, body mass index, reduced kidney function, hormone use, and inflammation) in regulating von Willebrand factor antigen (VWF:Ag) and factor VIII activity (FVIII:C) levels in the normal population.

METHODS

Analysis were performed in a large population sample (2923 individuals) from the Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis (MEGA study), after exclusion of individuals with active cancer and women who were pregnant or within nine months postpartum. The increase of VWF:Ag and FVIII:C with age was evaluated by linear regression after the age of 40 years. Analyses were adjusted for acquired factors and stratified for sex and blood group.

RESULTS

VWF:Ag and FVIII:C increased with age: increase per decade of age for VWF:Ag 18 IU/dL (95%CI 15-20) and for FVIII:C 12 IU/dL (95%CI 10-14). After adjustment for acquired factors, the increase per decade was 13 IU/dL (95%CI 10-16) for VWF:Ag and 9 IU/dL (95%CI 6-11) for FVIII:C. The stratified analysis for blood group showed higher increase in the non-O group, but these differences were annulled after adjustment for acquired factors.

CONCLUSIONS

VWF:Ag and FVIII:C increase with age. Carriers of blood group non-O present a steeper increase of VWF:Ag and FVIII:C with age, that is mediated by acquired factors.

Risk of cancer in patients with thyroid disease and venous thromboembolism

Objective

Risk of venous thromboembolism (VTE) is increased in patients with hypo/hyperthyroidism. It is unknown whether VTE may be a presenting symptom of occult cancer in these patients.

Design

Nationwide population-based cohort study based on Danish medical registry data.

Methods

We identified all patients diagnosed with VTE during 1978–2013 who had a previous or concurrent diagnosis of hypothyroidism (N=1481) or hyperthyroidism (N=1788). We followed them until a first-time cancer diagnosis, death, emigration, or study end, whichever came first. We calculated 1-year absolute cancer risk and standardized incidence ratios (SIRs) for cancer incidence in the study population compared with national cancer incidence in the general population.

Results

During the first year after a VTE diagnosis, the 1-year absolute cancer risk was 3.0% among patients with hypothyroidism and 3.9% among those with hyperthyroidism. During the first year of follow-up, SIRs for cancer in the study population compared with the general population were 1.96 (95% CI: 1.42–2.64) among patients with hypothyroidism and 2.67 (95% CI: 2.07–3.39) among those with hyperthyroidism. SIRs declined substantially after 1 year but remained increased during the remainder of the follow-up period (up to 36 years) (SIR for hypothyroidism=1.16 [95% CI: 0.97–1.39]; SIR for hyperthyroidism=1.26 [95% CI: 1.08–1.46]).

Conclusion

VTE may be a marker of underlying occult cancer in patients with hypothyroidism or hyperthyroidism.

New Interfaces of Thyroid Hormone Actions With Blood Coagulation and Thrombosis

Substantial clinical evidence indicates hyperthyroidism enhances coagulation and increases the risk of thrombosis. In vitro and clinical evidence implicate multiple mechanisms for this risk. Genomic actions of thyroid hormone as 3,5,3′-triiodo-L-thyronine (T₃) via a nuclear thyroid hormone receptor have been implicated, but recent evidence shows that nongenomic mechanisms initiated at the receptor for L-thyroxine (T₄) on platelet integrin αvβ3 are prothrombotic. The T₄-initiated mechanisms involve platelet activation and, in addition, cellular production of cytokines and chemokines such as CX3CL1 with procoagulatory activities. These procoagulant actions of T₄ are particulary of note because within cells T4 is not seen to be functional, but to be only a prohormone for T₃. Finally, it is also possible that thyroid hormone stimulates platelet-endothelial cell interaction involved in local thrombus generation. In this brief review, we survey mechanisms by which thyroid hormone is involved in coagulation and platelet functions. It is suggested that the threshold should be lowered for considering the possibility that clinically significant clotting may complicate hyperthyroidism. The value of routine measurement of partial thromboplastin time or circulating D-dimer in patients with hyperthyroid or in patients treated with thyrotropin-suppressing dosage of T₄ requires clinical testing.

The influence of thyroid function on the coagulation system and its clinical consequences

Several studies indicate that low plasma levels of thyroid hormone shift the hemostatic system towards a hypocoagulable and hyperfibrinolytic state, whereas high levels of thyroid hormone lead to more coagulation and less fibrinolysis. Low levels of thyroid hormone thereby seem to lead to an increased bleeding risk, whereas high levels, by contrast, increase the risk of venous thromboembolism. Hypothyroidism leads to a higher incidence of acquired von Willebrand's syndrome and with increasing levels of free thyroxine, levels of fibrinogen, factor VIII and von Willebrand factor, amongst others, increase gradually, to the extent that they may lead to symptomatic venous thromboembolism in patients with hyperthyroidism. Here, we discuss the literature on the effect of thyroid hormone on the hemostatic system and the associated risk of bleeding and venous thromboembolism. Patients with hypothyroidism are at increased risk of developing bleeding complications, which could be relevant in patients undergoing invasive procedures. Furthermore, physicians should be aware of the possibility of hyperthyroidism as an underlying risk factor for venous thromboembolism, especially in unexplained cases. Clinical studies are needed to further investigate the significance for general practice of these findings. Besides the effects of hyperthyroidism on venous thromboembolism, its effects on embolism secondary to atrial fibrillation are described.

Thyroid State Regulates Gene Expression in Human Whole Blood

CONTEXT

Despite the well-recognized clinical features resulting from insufficient or excessive thyroid hormone (TH) levels in humans, it is largely unknown which genes are regulated by TH in human tissues.

OBJECTIVE

To study the effect of TH on human gene expression profiles in whole blood, mainly consisting of T3 receptor (TR) α-expressing cells.

METHODS

We performed next-generation RNA sequencing on whole blood samples from eight athyroid patients (four females) on and after 4 weeks off levothyroxine replacement. Gene expression changes were analyzed through paired differential expression analysis and confirmed in a validation cohort. Weighted gene coexpression network analysis (WGCNA) was applied to identify thyroid state-related networks.

RESULTS

We detected 486 differentially expressed genes (fold-change >1.5; multiple testing corrected P value < 0.05), of which 76% were positively and 24% were negatively regulated. Gene ontology (GO) enrichment analysis revealed that three biological processes were significantly overrepresented, of which the process translational elongation showed the highest fold enrichment (7.3-fold, P = 1.8 × 10-6). WGCNA analysis independently identified various gene clusters that correlated with thyroid state. Further GO analysis suggested that thyroid state affects platelet function.

CONCLUSIONS

Changes in thyroid state regulate numerous genes in human whole blood, predominantly TRα-expressing leukocytes. In addition, TH may regulate gene transcripts in platelets.

The effect of hyperthyroidism on procoagulant, anticoagulant and fibrinolytic factors

Several coagulation and fibrinolytic parameters appear to be affected by thyroid hormone excess;however, the net effect on the haemostatic system remains unclear. We aimed to update our previous review and systematically summarise and meta-analyse the data by assessing the effects of thyrotoxicosis on the coagulation and fibrinolytic system in vivo. Data sources included MEDLINE (2006–2012), EMBASE (2006–2012), and reference lists. The sources were combined with our previous search containing studies from 1980–2006. Eligible studies were all observational or experimental studies. Two investigators independently extracted data and rated study quality. Weighted mean proportion and 95% confidence intervals were calculated and pooled using a fixed and a random-effects model. A total of 29 articles consisting of 51 studies were included, as in several articles more than one study was described. We included four intervention (before and after treatment in hyperthyroid patients), five cross-sectional (hyperthyroid subjects and euthyroid controls), and four experimental (before and after use of thyroid hormone in euthyroid subjects) medium/high quality studies for meta-analysis. We found that thyrotoxicosis shifts the haemostatic balance towards a hypercoagulable and hypofibrinolytic state with a rise in factors VIII and IX, fibrinogen, von Willebrand factor, and plasminogen activator inhibitor-1. This was observed in endogenous and exogenous thyrotoxicosis, and in subclinical as well as overt hyperthyroidism. We conclude that both subclinical and overt hyperthyroidism induce a prothrombotic state, which is therefore likely to be a risk factor for venous thrombosis.

Hemostasis in Overt and Subclinical Hyperthyroidism

CONTEXT

There are contradictory results on the effect of hyperthyroidism on hemostasis. Inadequate population-based studies limited their clinical implications, mainly on the risk of venous thromboembolism (VTE). The present review focuses on hemostatic changes in overt and subclinical hyperthyroidism.

METHODS

A systematic literature search was conducted employing MEDLINE database. The following words were used for the search: Hyperthyroidism; thyrotoxicosis; Graves disease; goiter, nodular; hemostasis; blood coagulation factors; blood coagulation disorders; venous thromboembolism; bleeding; fibrinolysis. The articles that were related to hyperthyroidism and hemostasis are used in this manuscript.

RESULTS

Hyperthyroidism, either overt or subclinical, renders a hypercoagulable state, although there are several studies with contradictory findings in the literature. Hypercoagulability may be caused by an increase in the level of various coagulation factors such as factor (F) VIII, FX, FIX, von Willebrand F (vWF), and fibrinogen, while hypofibrinolysis by changes in coagulation parameters such as a decrease in plasmin and plasmin activator or an increase in α2-antiplasmin, plasminogen activator inhibitor-1 and thrombin activatable fibrinolysis inhibitor.

CONCLUSIONS

Although many reports are in favor of a hypercoagulable state in overt hyperthyroidism but this finding at the biochemical level and its clinical implication, on the occurrence of VTE, has yet to be confirmed.

Plasma Levels of Free Thyroxine and Risk of Major Bleeding in Bariatric Surgery

BACKGROUND

In a recent study of patients using vitamin K antagonists, those with low free thyroxin (FT4) levels within the normal range had a 3- to 5-fold increased risk of major bleeding. We tested the hypothesis that low levels of preoperative FT4 within the reference range are associated with an increased risk of major bleeding during and after bariatric surgery.

METHODS

The charts of 2,872 consecutive patients undergoing bariatric surgery were retrospectively screened for bleeding episodes. Patients with major bleeding until 1 month after surgery were compared to randomly selected control patients without bleeding, in a ratio of 1:4. We evaluated the association between preoperative FT4 levels and the risk of major bleeding by logistic regression.

RESULTS

Seventy-two cases (2.5%) with major bleeding were identified and 288 controls were selected. The median plasma level of FT4 was 13 pmol/l (interquartile range: 12-14) in the cases as well as in the controls. No clear effect was observed of low levels of FT4 on the risk of major bleeding: odds ratio 1.48 (95% CI: 0.46-4.80) for patients with an FT4 level <11 pmol/l, 1.03 (0.49-2.18) for patients with an FT4 level <12 pmol/l, and 1.12 (0.65-1.94) for patients with an FT4 level <13 pmol/l as compared to patients with FT4 values greater than or equal to these cutoff levels.

INTERPRETATION

We did not observe an increased risk of major bleeding with low levels of FT4 in patients undergoing bariatric surgery.

Thyroid function, as assessed by TSH, and future risk of venous thromboembolism: the Tromsø study

OBJECTIVE

The relationship between thyroid function and the risk of venous thromboembolism (VTE) has not been addressed in population-based cohorts. We investigated the association between TSH levels and the risk of VTE in a general adult population.

DESIGN

Population-based cohort study.

METHODS

TSH was measured in 11 962 subjects aged 25-89 years who participated in Tromsø 4-6 starting in 1994-1995. Incident VTE events were recorded through 31st December 2010. Cox's regression models with TSH as a time-varying covariate were used to calculate hazard ratios (HRs) of VTE by TSH categories (low TSH: <0.05  mU/l; moderately reduced TSH: 0.05-0.19  mU/l; normal TSH: 0.20-4.00  mU/l; moderately elevated TSH: 4.01-5.00  mU/l; and high TSH: >5.00 mU/l) and within the normal range of TSH, modeling TSH as a continuous variable.

RESULTS

There were 289 VTEs during 8.2 years of median follow-up. Subjects with low (prevalence: 0.22%) and high (3.01%) TSH had slightly higher risk estimates for VTE than did subjects with normal TSH (multivariable HRs: 2.16, 95% CI 0.69-6.76 and 1.55, 95% CI 0.87-2.77 respectively), but the CIs were wide. Moreover, there was no association between TSH within the normal range and VTE (HR per 1 mU/l increase: 0.95, 95% CI 0.82-1.11).

CONCLUSION

Serum levels of TSH within the normal range were not associated with a risk of VTE, whereas low and high TSH levels were rare and associated with a moderately higher risk of VTE. The present findings suggest that only a minor proportion of the VTE risk in the population can be attributed to thyroid dysfunction.

Prothrombotic changes due to an increase in thyroid hormone levels

OBJECTIVE

With increasing free thyroxine levels, a gradually rising risk of venous thromboembolism has been described in case-control studies. However, reports on the influence of thyroid hormones on haemostasis, while suggesting a hypercoagulable state in thyrotoxicosis, have often been inconclusive. This study evaluates multiple markers of haemostasis and fibrinolysis in a paired design, making it more sensitive to changes in thyroid hormone levels.

DESIGN

We analysed multiple variables in patients who shifted from severe hypothyroidism to mild hyperthyroidism during thyroid cancer treatment. Those with possible residual disease were excluded.

METHODS

Ninety patients following total thyroidectomy were tested on two occasions: i) before radioiodine remnant ablation and ii) 6 weeks later, on levothyroxine (lT4) suppression treatment, and the results were compared using the Wilcoxon's test for paired data.

RESULTS

During lT4 treatment, significant increases (all P<0.001) in fibrinogen (from median 3.4 to 3.8 g/l), von Willebrand factor (from 85 to 127%), factor VIII (from 111 to 148%) and plasminogen activator inhibitor 1 (from 6.5 to 13.9 μg/l) were observed. In addition, the activation times of platelet adhesion and aggregation stimulated with collagen and epinephrine (EPI)/ADP, i.e. closure times in platelet function analyser (PFA-100), were significantly shortened (P<0.001): for EPI from median 148 to 117 s and for ADP from 95 to 80 s. Changes in other tests were less prominent or insignificant.

CONCLUSIONS

An increase in thyroid hormone levels shifts the haemostatic balance towards a hypercoagulable, hypofibrinolytic state. This may contribute to the increased cardiovascular morbidity and mortality observed even in mild thyrotoxicosis.

Elucidating mechanisms of toxicity using phenotypic data from primary human cell systems--a chemical biology approach for thrombosis-related side effects

Here we describe a chemical biology approach for elucidating potential toxicity mechanisms for thrombosis-related side effects. This work takes advantage of a large chemical biology data set comprising the effects of known, well-characterized reference agents on the cell surface levels of tissue factor (TF) in a primary human endothelial cell-based model of vascular inflammation, the BioMAP^® 3C system. In previous work with the Environmental Protection Agency (EPA) for the ToxCast™ program, aryl hydrocarbon receptor (AhR) agonists and estrogen receptor (ER) antagonists were found to share an usual activity, that of increasing TF levels in this system. Since human exposure to compounds in both chemical classes is associated with increased incidence of thrombosis-related side effects, we expanded this analysis with a large number of well-characterized reference compounds in order to better understand the underlying mechanisms. As a result, mechanisms for increasing (AhR, histamine H1 receptor, histone deacetylase or HDAC, hsp90, nuclear factor kappa B or NFκB, MEK, oncostatin M receptor, Jak kinase, and p38 MAPK) and decreasing (vacuolar ATPase or V-ATPase) and mTOR) TF expression levels were uncovered. These data identify the nutrient, lipid, bacterial, and hypoxia sensing functions of autophagy as potential key regulatory points controlling cell surface TF levels in endothelial cells and support the mechanistic hypothesis that these functions are associated with thrombosis-related side effects in vivo.

High levels of procoagulant factors mediate the association between free thyroxine and the risk of venous thrombosis: the MEGA study

BACKGROUND

Thyroid hormone affects the coagulation system, but its effect on clinical disease is not clear. We determined the associations of levels of free thyroxine (FT4), thyroid-stimulating hormone (TSH) and anti-thyroid peroxidase antibodies (antiTPO) with levels of coagulation factors and the risk of venous thrombosis.

METHODS

In a large population based case-control study (Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis study) on the etiology of venous thrombosis, we determined the levels of FT4, TSH, antiTPO, factor FII, FVII, FVIII, FIX, FX, von Willebrand factor (VWF), antithrombin, protein C, protein S and fibrinogen in 2177 cases and 2826 controls.

RESULTS

High levels of FT4 were associated with increased concentrations of procoagulant factors, and not with levels of anticoagulant factors. High levels of FT4 were also associated with the risk of venous thrombosis, up to an odds ratio (OR) of 2.2 (95% confidence interval [CI] 1.0-4.6) for levels above 24.4 pm relative to FT4 levels between 15.5 and 18.9 pm. In 11 cases and one control, clinical hyperthyroidism had been diagnosed within a year of the thrombotic event, leading to an OR of 17.0 (95% CI 2.2-133.0) for thrombosis. The ORs approached unity after adjustment for FVIII and VWF, which suggests that the effect was mediated by these factors. Low TSH levels were also, but less evidently, associated with thrombosis, whereas there was no association between antiTPO and venous thrombosis risk.

CONCLUSIONS

High levels of FT4 increase the concentrations of the procoagulant proteins FVIII, FIX, fibrinogen, and VWF, and by this mechanism increase the risk of venous thrombosis.

Major Haemorrhage during Vitamin K Antagonist Treatment: The Influence of Thyroid Hormone Levels

BACKGROUND

Annually, approximately 1-3% of patients treated with vitamin K antagonists (VKA) suffer from major haemorrhage. Since high levels of free thyroxine (fT4) are associated with increased thrombosis risk, the aim was to assess whether low levels of fT4 contribute to major haemorrhage in patients under VKA treatment.

METHODS

The FACTORS (Factors in Oral Anticoagulant Safety) study is a case-control study on patients receiving VKA treatment, including 110 cases with major haemorrhage. Controls were 220 matched participants treated with VKA without major haemorrhage. Odds ratios (OR) and 95% confidence intervals (95% CI) for the association of fT4 levels with major haemorrhage were calculated for different fT4 cutoffs by conditional logistic regression.

RESULTS

In patients with an fT4 level below 13 pmol/l, the risk of major haemorrhage was 5-fold increased (OR = 5.1; 95% CI: 0.9-28.6) compared with patients with an fT4 level above 13 pmol/l. At a cutoff of 14 pmol/l, the risk was 3-fold increased (OR = 2.9; 95% CI: 1.0-8.5). High levels of fT4 did not affect bleeding risk. No clear effect of thyroid-stimulating hormone and thyroid peroxidase antibodies was seen on the risk of major haemorrhage.

CONCLUSIONS

These results indicate that fT4 levels below 14 pmol/l play a role in the aetiology of major haemorrhage in VKA users.