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Original Investigation |

Hyperhomocyst(e)inemia and the Increased Risk of Venous Thromboembolism:  More Evidence From a Case-Control Study FREE

Loralie J. Langman, PhD; Joel G. Ray, MD, FRCPC; Jovan Evrovski, PhD; Erik Yeo, MD, FRCPC; David E.C. Cole, MD, FRCPC
[+] Author Affiliations

From the Departments of Medicine (Drs Langman, Ray, Yeo, and Cole), Laboratory Medicine and Pathobiology (Drs Langman, Evrovski, Yeo, and Cole), and Paediatrics (Genetics) (Dr Cole), University of Toronto, Toronto, Ontario; the Departments of Hematology (Dr Yeo) and Clinical Chemistry (Dr Cole), The Toronto Hospital, Toronto; and the Department of Clinical Epidemiology and Biostatistics (Dr Ray), McMaster University, Hamilton, Ontario.


Arch Intern Med. 2000;160(7):961-964. doi:10.1001/archinte.160.7.961.
Text Size: A A A
Published online

Background  Elevation of plasma homocyst(e)ine level is an independent risk factor for arterial and venous thrombosis. We studied the degree to which hyperhomocyst(e)inemia contributes to the development of venous thromboembolism, using a retrospective case-control study design.

Methods  Cases were individuals with objectively confirmed venous thromboembolism and no history of atherosclerosis seen at the Toronto Hospital Thrombosis Clinic, Toronto, Ontario, between January 1, 1996, and July 31, 1998. Three controls were matched for every case according to sex and age within 5 years and were derived from a large community cohort. All subjects underwent assessment for fasting plasma homocyst(e)ine levels. Hyperhomocyst(e)inemia was defined as a fasting total homocyst(e)ine concentration above the 95th percentile control value.

Results  Seventy cases and 210 matched controls were included. Men and women were equally represented, and most were younger than 60 years. Among cases with venous thromboembolism, the mean (± SD) plasma homocyst(e)ine level was significantly higher than in controls (13.0 ± 6.9 µmol/L vs 9.0 ± 4.8 µmol/L, respectively; P<.001). Sixteen (23%) of 70 cases had hyperhomocyst(e)inemia compared with 10 (5%) of 210 controls (odds ratio, 5.9; 95% confidence interval [CI], 2.5-13.8). Among subjects aged 60 years or younger, the odds ratio was 4.9 (95% CI, 1.4-16.4), while for those aged 60 years or older, it was 7.3 (95% CI, 2.2-24.0). Even with the exclusion of cases showing abnormal renal function or low serum vitamin B12 or folate levels, the odds ratio remained significantly elevated at 3.3 (95% CI, 1.1-10.0).

Conclusions  We found that fasting hyperhomocyst(e)inemia is a significant risk factor for venous thromboembolic disease in patients at a thrombosis clinic. Given the magnitude of effect and consistency across these studies, it is likely that homocyst(e)ine plays a causative role in the development of venous thrombosis, and it should be considered in the workup for venous thromboembolism.

Figures in this Article

THE ROLE of mild to moderate hyperhomocyst(e)inemia (hyper-Hcy) in the development of vascular disease has been documented and reviewed extensively.15 Unlike some thrombophilia defects, hyper-Hcy is associated with both venous6 and arterial7 thrombosis. In a recent meta-analysis, including 9 published studies, Ray6 found that hyper-Hcy was a significant risk factor for venous thromboembolism (VTE), with a pooled odds ratio (OR) of 2.95 (95% confidence interval [CI], 2.08-4.17).8,9 In the subgroup analysis, the OR appeared to be higher among patients with VTE before 60 years of age (OR, 4.13; 95% CI, 1.25-13.72).6

In the current study, we examined whether hyper-Hcy is a risk factor for VTE in a thrombosis clinic population, with an effort to respond to the apparent limitations of previous studies.6 Specifically, we also omitted subjects with abnormal serum creatinine, folate, and vitamin B12 levels, which are known to influence plasma total homocyst(e)ine (Hcy) levels.1012

We conducted a case-control study of subjects prospectively recruited from the Toronto Hospital Thrombosis Clinic, Toronto, Ontario, between January 1, 1996, and July 31, 1998. Cases were individuals seen as outpatients with objectively confirmed VTE and no history of atherosclerosis. Venous thromboembolism was confirmed by the following techniques: for deep vein thrombosis, duplex ultrasonography and rarely venography; for pulmonary embolism, ventilation-perfusion scan; for VTE in the inferior vena cava, computed tomography with venous phase contrast or Doppler ultrasound; for VTE in the upper arm, Doppler ultrasound; and for intracranial VTE, magnetic resonance imaging. Three controls were matched for every case, according to both sex and age within 5 years, and were from a convenience sample derived from a large community cohort of ambulatory adults whose primary care physicians had ordered measurement of plasma total Hcy.13 Specific health details, including history of VTE or vitamin supplementation, or reasons for testing of controls, were not available. None of the cases were prescribed vitamin supplements, although some may have been taking over-the-counter vitamin supplements on their own.

Subjects were instructed to fast for at least 8 hours before collection of whole blood anticoagulated with EDTA; the blood was placed on ice and the plasma was separated within 2 hours of venipuncture. Plasma was frozen at −70°C until analysis. Plasma total Hcy was measured by high-performance liquid chromatography, with electrochemical detection and pulsed integrated amperometry.14,15 Serum creatinine was measured by the Jaffe method on an autoanalyzer (AU800; Olympus Diagnostic Systems, Melleville, NY), while serum folate and vitamin B12 were measured by radioimmunoassay (Quantaphase II; Bio-Rad Laboratories Inc, Toronto). Activated protein C resistance16 and antiphospholipid antibodies were measured by previously described techniques17 (Sanofi ACA kit 31057; Sanofi Diagnostics, Redmond, Wash).

Mean values of plasma total Hcy were compared between cases and controls by the t test with a 2-sided P value of .05. Hyperhomocyst(e)inemia was defined as a value above the 95th percentile of controls. The crude ORs, along with 95% CIs, were calculated for cases and control groups. The calculated OR for the presence of hyper-Hcy among subjects aged 60 years or younger was measured as a secondary outcome. In a third analysis, cases with a serum creatinine level greater than 150 µmol/L (1.7 mg/dL), serum folate level less than 4.1 nmol/L, or serum vitamin B12 level less than 100 pmol/L were excluded, and the ORs were recalculated.

Data were analyzed by the SPSS 7.5 software package (SPSS Inc, Chicago, Ill) and Instat (GraphPad version 3.0; GraphPad Software Inc, San Diego, Calif). On the basis of previously published studies,6 we fixed the prevalence of hyper-Hcy in the unaffected control group at 5%, and we estimated that a tripling of this value among cases with VTE, equivalent to an OR of 3.0, would be clinically important. With a 2-sided α of .05 and β of .50, and an availability of at least twice as many controls as cases, we estimated that 70 cases and 140 controls would be required for our study. Since 3 controls were available for each case, we included 70 cases and 210 controls.

The OR (and 95% CI) obtained with data pooled from this study and those previously used in Ray's meta-analysis6 was calculated, using the random effects model of DerSimonian and Laird.8 Heterogeneity across the studies was assessed by visual inspection and statistical analysis,9 with a threshold P value of .10.

Of the 70 cases and 210 controls, men and women were equally represented, and the majority of subjects were less than 60 years of age (Table 1). Most cases had experienced either deep vein thrombosis or pulmonary embolism, of whom 13 (19%) of all cases had recurrent disease. Twenty (29%) of the cases had either activated protein C resistance or antiphospholipid antibodies as an identified thrombophilic defect, but none had both. Almost half of all cases had another predisposing factor for VTE (Table 1). The mean (± SD) plasma total Hcy level was not statistically different between male and female cases (13.2 ± 8.0 µmol/L vs 12.8 ± 6.1 µmol/L; P=.78) or between male and female controls (9.1 ± 5.5 µmol/L vs 8.9 ± 4.3 µmol/L; P=.72). Among the 70 cases, the mean plasma total Hcy level (13.0 ± 6.9 µmol/L) was significantly higher than for controls (9.0 ± 4.8 µmol/L; P<.001) (Table 1). The 95th percentile for control Hcy level was 14.8 µmol/L (Figure 1). Of the 70 cases, 16 (23%) had total Hcy levels above this 95th percentile value, compared with 10 controls (5%) (OR, 5.9; 95% CI, 2.5-13.8) (Figure 1, Table 2).

Table Graphic Jump LocationTable 1. Characteristics of Study Cases and Controls*
Place holder to copy figure label and caption

Distribution of total plasma homocyst(e)ine (tHcy) concentrations in cases (black bars) and controls (gray bars). The 95th percentile for the control group (14.8 µmol/L) is shown as a dashed line.

Graphic Jump Location
Table Graphic Jump LocationTable 2. Risk of VTE in the Presence of Hyper-Hcy*

With exclusion of subjects aged 60 years or older, the OR was 4.9 (95% CI, 1.4-16.4), while for those aged 60 years or older, it was higher (OR, 7.3; 95% CI, 2.2-24.0) (Table 2). On the exclusion of cases whose baseline serum vitamin B12 level was less than 100 pmol/L (2/62 [3%]); serum folate level, less than 4.1 nmol/L (1/64 [2%]); and serum creatinine level, greater than 150 µmol/L (1.7 mg/dL) (6/65 [9%]); the OR for VTE in the presence of hyper-Hcy remained significant (OR, 3.3; 95% CI, 1.1-10.0) (Table 2). Combining our data with those from 9 published studies,6 the pooled OR is 3.3 (95% CI, 2.3-4.6), with an absence of statistical heterogeneity (P=.42).

Our findings add to the observational evidence examining the relationship between hyper-Hcy and VTE.6 Given the consistency and the magnitude of the pooled OR across these 10 studies, it seems likely that elevated plasma total Hcy level is a clinically significant factor in the development of VTE. Hyperhomocyst(e)inemia may cause vessel wall endothelial dysfunction,18 vascular smooth muscle proliferation,19 and hemostatic changes consistent with the prothrombotic state.20 Such changes can be mimicked in vitro by exposure of cells or tissues to homocyst(e)ine.21,22 These lend support for a causal link that would explain the epidemiological association of hyper-Hcy with VTE we describe herein.23

Our study derived an OR of 5.9 for VTE in the presence of hyper-Hcy, redefining the pooled OR for all 10 studies to 3.3; but are these figures clinically important? Some argue that an OR above 2.0 influences clinical practice.24 However, clinical significance also depends on how common and lethal both exposure and disease are, as well as the magnitude of resources required for their detection, treatment, and prevention.25 Venous thromboembolism is a serious condition, and plasma total Hcy measurement is increasingly offered by routine diagnostic centers. Studies are now under way to evaluate the therapeutic efficacy of folate and vitamins B6 and B12 in the secondary prevention of VTE.26 Considering these factors, it can be argued that a fasting plasma total Hcy measurement should be part of any thrombophilia workup.

A striking aspect of hyper-Hcy is its association with earlier-onset, often severe vascular disease, particularly with a positive family history.6 However, our study fails to support this finding, as the OR was less pronounced among patients younger than 60 years compared with older adults. Thus, hyper-Hcy may be an important VTE risk factor regardless of age. Several publications confirm a high frequency of clinically silent vitamin B12 deficiency in geriatric populations, even those with apparently "normal" vitamin B12 levels.27,28 Willems and colleagues29 also noted a higher frequency of hyper-Hcy among a group of elderly adults with VTE, compared with disease-free controls of approximately the same age (OR, 2.4; 95% CI, 0.8-6.9).

Our study has several limitations and certain strengths. Although we attempted to match cases with controls for age and sex, we were unable to control for other factors known to affect plasma total Hcy level, such as renal insufficiency or vitamin supplementation.30 Studies have shown that homocyst(e)ine level is strongly correlated with serum creatinine level and inversely related to glomerular filtration.31 Several cases had cancer, were undergoing hemodialysis, or had received organ transplants, any of which could raise plasma total Hcy levels30 and increase the risk for vascular disease.32,33 Also of concern is the lack of information on the reasons leading to plasma total Hcy measurement in controls. However, if some controls had also experienced a previous VTE or atherosclerotic event, or had renal insufficiency, we would have expected to find a greater frequency of hyper-Hcy and, accordingly, a deflation in the OR.

Since the cause of VTE remains multifactorial, future research should evaluate the risk for VTE in the presence of hyper-Hcy and other common risk factors, such as activated protein C resistance, antiphospholipid antibodies, and defects in protein C, protein S, or antithrombin III,34,35 or a family history of VTE.36 Furthermore, a significant proportion of the general population carries heterozygous or homozygous genetic mutations associated with hyper-Hcy,35,37 which may be relevant and which warrants further study.

Therapeutic trials of Hcy reduction for the secondary prevention of atherosclerosis and VTE, or trials aimed at reducing plasma total Hcy level among asymptomatic individuals, should enable physicians and researchers to establish the importance of homocyst(e)ine measurement in the clinical domain.

Accepted for publication June 29, 1999.

This study was supported by grant NA-3030 from the Heart and Stroke Foundation of Ontario, Ottawa (Dr Cole).

Reprints: David E. C. Cole, MD, FRCPC, Room 402, Banting Institute, 100 College St, Toronto, Ontario, Canada M5G 1L5 (e-mail: davidec.cole@utoronto.ca).

Malinow  MR Plasma homocyst(e)ine and arterial occlusive diseases: a mini-review. Clin Chem. 1995;41173- 176
Malinow  MR Hyperhomocyst(e)inemia: a common and easily reversible risk factor for occlusive atherosclerosis. Circulation. 1990;812004- 2006
Link to Article
Frohlich  JJ Lipoproteins and homocyst(e)ine as risk factors for atherosclerosis: assessment and treatment. Can J Cardiol. 1995;1118C- 23C
Malinow  MR Homocyst(e)ine and arterial occlusive diseases. J Intern Med. 1994;236603- 617
Link to Article
Fortin  L-JGenest  J  Jr Measurement of homocyst(e)ine in the prediction of arteriosclerosis. Clin Biochem. 1995;28155- 162
Link to Article
Ray  JG Meta-analysis of hyperhomocysteinemia as a risk factor for venous thromboembolic disease. Arch Intern Med. 1998;1582101- 2106
Link to Article
den Heijer  MKoster  TBlom  HJ  et al.  Hyperhomocysteinemia as a risk factor for deep-vein thrombosis. N Engl J Med. 1996;334759- 762
Link to Article
DerSimonian  RLaird  N Meta-analysis in clinical trials. Control Clin Trials. 1986;7177- 188
Link to Article
Breslow  NEDay  NE Statistical Methods in Cancer Research, Volume I: The Analysis of Case-Control Studies  Lyon, France International Agency for Research on Cancer1980;1- 406
Guttormsen  ABSchneede  JFiskerstrand  TUeland  PMRefsum  HM Plasma concentrations of homocysteine and other aminothiol compounds are related to food intake in healthy human subjects. J Nutr. 1994;1241934- 1941
Ubbink  JB Vitamin nutrition status and homocysteine: an atherogenic risk factor. Nutr Rev. 1994;52383- 393
Link to Article
Nygard  ORefsum  HUeland  PMVollset  SE Major lifestyle determinants of plasma total homocysteine distribution: the Hordaland Homocysteine Study. Am J Clin Nutr. 1998;67263- 270
Miner  SESRoss  HJLangman  LJ  et al.  Total plasma homocysteine concentrations are strongly correlated with whole blood cyclosporine levels and angiographic coronary artery disease in heart transplant patients [abstract]. Transplantation. 1998;9 ((suppl)) 103S
Link to Article
Evrovski  JCallaghan  MCole  DEC Determination of homocysteine by HPLC with pulsed integrated amperometry. Clin Chem. 1995;41757- 758
Cole  DECLehotay  DCEvrovski  J Simplified simultaneous assay of total homocysteine and methionine by HPLC and pulsed integrated amperometry. Clin Chem. 1998;44188- 190
Svensson  PJDahlback  B Resistance to activated protein C as a basis for venous thrombosis. N Engl J Med. 1994;330517- 522
Link to Article
Alving  BMBaldwin  PERichards  RLJackson  BJ The dilute phospholipid APTT: a sensitive assay for verification of lupus anticoagulants. Thromb Haemost. 1985;54709- 712
Chambers  JCMcGregor  AJean-Marie  JKooner  JS Acute hyperhomocysteinaemia and endothelial dysfunction. Lancet. 1998;35136- 37
Link to Article
Tsai  JCPerrella  MAYoshizumi  M  et al.  Promotion of vascular smooth muscle cell growth by homocysteine: a link to atherosclerosis. Proc Natl Acad Sci U S A. 1994;916369- 6373
Link to Article
Rees  MMRodgers  GM Homocysteinemia: association of a metabolic disorder with vascular disease and thrombosis. Thromb Res. 1993;71337- 359
Link to Article
McCully  KS Chemical pathology of homocysteine, I: atherogenesis. Ann Clin Lab Sci. 1993;23477- 493
Lentz  SRSadler  JE Inhibition of thrombomodulin surface expression and protein C activation by the thrombogenic agent homocysteine. J Clin Invest. 1991;881906- 1914
Link to Article
Miner  SESEvrovski  JCole  DEC Clinical chemistry and molecular biology of homocysteine metabolism: an update. Clin Biochem. 1997;30189- 201
Link to Article
Burnand  BKernan  WNFeinstein  AR Indexes and boundaries for "quantitative significance" in statistical decisions. J Clin Epidemiol. 1990;431273- 1284
Link to Article
Taubes  G Epidemiology faces its limits. Science. 1995;269164- 169
Link to Article
Willems  HPJGerrits  WBJRosendaal  FRden Heijer  MBlom  HJBos  GMJ The VITRO trial: study design [abstract]. Neth J Med. 1998;52 ((suppl)) 43S
Brattstrom  LLindgren  AIsraelsson  BAndersson  AHultberg  B Homocysteine and cysteine: determinants of plasma levels in middle-aged and elderly subjects. J Intern Med. 1994;236633- 641
Link to Article
Naurath  HJJoosten  EReizler  RStabler  SPAllen  RHLindenbaum  J Effects of vitamin B12, folate, and vitamin B6 supplements in elderly people with normal serum vitamin concentrations. Lancet. 1995;34685- 89
Link to Article
Willems  HPJHavekes  MBerenchot  H  et al.  Homocysteine as a risk factor for venous thrombosis in the elderly [abstract]. Neth J Med. 1998;52 ((suppl)) 32S
Arnadottir  MHultberg  BNilsson-Ehle  PThysell  H The effect of reduced glomerular filtration rate on plasma total homocysteine concentration. Scand J Clin Lab Invest. 1996;5641- 46
Link to Article
Hultberg  BAndersson  ASterner  G Plasma homocysteine in renal failure. Clin Nephrol. 1993;40230- 235
Prandoni  PLensing  AWBuller  HR  et al.  Deep-vein thrombosis and the incidence of subsequent symptomatic cancer. N Engl J Med. 1992;3271128- 1133
Link to Article
Robinson  KGupta  ADennis  VW  et al.  Hyperhomocysteinemia confers an independent increased risk of atherosclerosis in end-stage renal disease and is closely linked to plasma folate and pyridoxine concentrations. Circulation. 1996;942743- 2748
Link to Article
Ridker  PMHennekens  CHSelhub  JMiletich  JPMalinow  MRStampfer  MJ Interrelation of hyperhomocyst(e)inemia, factor V Leiden, and risk of future venous thromboembolism. Circulation. 1997;951777- 1782
Link to Article
den Heijer  MWillems  HPJRosendaal  FR  et al.  Homocysteine, serum folate, mutated methyenetetrahydrofolate reductase (MTHFR) and factor V Leiden and the risk of venous thrombosis [abstract]. Neth J Med. 1998;52 ((suppl)) 25S
Briet  Evan der Meer  FJRosendaal  FRHouwing-Duistermaat  JJvan Houwelingen  HC Family history and inherited thrombophilia [letter]. Br J Haematol. 1995;89691
Link to Article
Kuo  LDavis  MJCannon  MSChilian  WM Pathophysiological consequences of atherosclerosis extend into the coronary microcirculation: restoration of endothelium-dependent responses by L-arginine. Circ Res. 1992;70465- 476
Link to Article

Figures

Place holder to copy figure label and caption

Distribution of total plasma homocyst(e)ine (tHcy) concentrations in cases (black bars) and controls (gray bars). The 95th percentile for the control group (14.8 µmol/L) is shown as a dashed line.

Graphic Jump Location

Tables

Table Graphic Jump LocationTable 1. Characteristics of Study Cases and Controls*
Table Graphic Jump LocationTable 2. Risk of VTE in the Presence of Hyper-Hcy*

References

Malinow  MR Plasma homocyst(e)ine and arterial occlusive diseases: a mini-review. Clin Chem. 1995;41173- 176
Malinow  MR Hyperhomocyst(e)inemia: a common and easily reversible risk factor for occlusive atherosclerosis. Circulation. 1990;812004- 2006
Link to Article
Frohlich  JJ Lipoproteins and homocyst(e)ine as risk factors for atherosclerosis: assessment and treatment. Can J Cardiol. 1995;1118C- 23C
Malinow  MR Homocyst(e)ine and arterial occlusive diseases. J Intern Med. 1994;236603- 617
Link to Article
Fortin  L-JGenest  J  Jr Measurement of homocyst(e)ine in the prediction of arteriosclerosis. Clin Biochem. 1995;28155- 162
Link to Article
Ray  JG Meta-analysis of hyperhomocysteinemia as a risk factor for venous thromboembolic disease. Arch Intern Med. 1998;1582101- 2106
Link to Article
den Heijer  MKoster  TBlom  HJ  et al.  Hyperhomocysteinemia as a risk factor for deep-vein thrombosis. N Engl J Med. 1996;334759- 762
Link to Article
DerSimonian  RLaird  N Meta-analysis in clinical trials. Control Clin Trials. 1986;7177- 188
Link to Article
Breslow  NEDay  NE Statistical Methods in Cancer Research, Volume I: The Analysis of Case-Control Studies  Lyon, France International Agency for Research on Cancer1980;1- 406
Guttormsen  ABSchneede  JFiskerstrand  TUeland  PMRefsum  HM Plasma concentrations of homocysteine and other aminothiol compounds are related to food intake in healthy human subjects. J Nutr. 1994;1241934- 1941
Ubbink  JB Vitamin nutrition status and homocysteine: an atherogenic risk factor. Nutr Rev. 1994;52383- 393
Link to Article
Nygard  ORefsum  HUeland  PMVollset  SE Major lifestyle determinants of plasma total homocysteine distribution: the Hordaland Homocysteine Study. Am J Clin Nutr. 1998;67263- 270
Miner  SESRoss  HJLangman  LJ  et al.  Total plasma homocysteine concentrations are strongly correlated with whole blood cyclosporine levels and angiographic coronary artery disease in heart transplant patients [abstract]. Transplantation. 1998;9 ((suppl)) 103S
Link to Article
Evrovski  JCallaghan  MCole  DEC Determination of homocysteine by HPLC with pulsed integrated amperometry. Clin Chem. 1995;41757- 758
Cole  DECLehotay  DCEvrovski  J Simplified simultaneous assay of total homocysteine and methionine by HPLC and pulsed integrated amperometry. Clin Chem. 1998;44188- 190
Svensson  PJDahlback  B Resistance to activated protein C as a basis for venous thrombosis. N Engl J Med. 1994;330517- 522
Link to Article
Alving  BMBaldwin  PERichards  RLJackson  BJ The dilute phospholipid APTT: a sensitive assay for verification of lupus anticoagulants. Thromb Haemost. 1985;54709- 712
Chambers  JCMcGregor  AJean-Marie  JKooner  JS Acute hyperhomocysteinaemia and endothelial dysfunction. Lancet. 1998;35136- 37
Link to Article
Tsai  JCPerrella  MAYoshizumi  M  et al.  Promotion of vascular smooth muscle cell growth by homocysteine: a link to atherosclerosis. Proc Natl Acad Sci U S A. 1994;916369- 6373
Link to Article
Rees  MMRodgers  GM Homocysteinemia: association of a metabolic disorder with vascular disease and thrombosis. Thromb Res. 1993;71337- 359
Link to Article
McCully  KS Chemical pathology of homocysteine, I: atherogenesis. Ann Clin Lab Sci. 1993;23477- 493
Lentz  SRSadler  JE Inhibition of thrombomodulin surface expression and protein C activation by the thrombogenic agent homocysteine. J Clin Invest. 1991;881906- 1914
Link to Article
Miner  SESEvrovski  JCole  DEC Clinical chemistry and molecular biology of homocysteine metabolism: an update. Clin Biochem. 1997;30189- 201
Link to Article
Burnand  BKernan  WNFeinstein  AR Indexes and boundaries for "quantitative significance" in statistical decisions. J Clin Epidemiol. 1990;431273- 1284
Link to Article
Taubes  G Epidemiology faces its limits. Science. 1995;269164- 169
Link to Article
Willems  HPJGerrits  WBJRosendaal  FRden Heijer  MBlom  HJBos  GMJ The VITRO trial: study design [abstract]. Neth J Med. 1998;52 ((suppl)) 43S
Brattstrom  LLindgren  AIsraelsson  BAndersson  AHultberg  B Homocysteine and cysteine: determinants of plasma levels in middle-aged and elderly subjects. J Intern Med. 1994;236633- 641
Link to Article
Naurath  HJJoosten  EReizler  RStabler  SPAllen  RHLindenbaum  J Effects of vitamin B12, folate, and vitamin B6 supplements in elderly people with normal serum vitamin concentrations. Lancet. 1995;34685- 89
Link to Article
Willems  HPJHavekes  MBerenchot  H  et al.  Homocysteine as a risk factor for venous thrombosis in the elderly [abstract]. Neth J Med. 1998;52 ((suppl)) 32S
Arnadottir  MHultberg  BNilsson-Ehle  PThysell  H The effect of reduced glomerular filtration rate on plasma total homocysteine concentration. Scand J Clin Lab Invest. 1996;5641- 46
Link to Article
Hultberg  BAndersson  ASterner  G Plasma homocysteine in renal failure. Clin Nephrol. 1993;40230- 235
Prandoni  PLensing  AWBuller  HR  et al.  Deep-vein thrombosis and the incidence of subsequent symptomatic cancer. N Engl J Med. 1992;3271128- 1133
Link to Article
Robinson  KGupta  ADennis  VW  et al.  Hyperhomocysteinemia confers an independent increased risk of atherosclerosis in end-stage renal disease and is closely linked to plasma folate and pyridoxine concentrations. Circulation. 1996;942743- 2748
Link to Article
Ridker  PMHennekens  CHSelhub  JMiletich  JPMalinow  MRStampfer  MJ Interrelation of hyperhomocyst(e)inemia, factor V Leiden, and risk of future venous thromboembolism. Circulation. 1997;951777- 1782
Link to Article
den Heijer  MWillems  HPJRosendaal  FR  et al.  Homocysteine, serum folate, mutated methyenetetrahydrofolate reductase (MTHFR) and factor V Leiden and the risk of venous thrombosis [abstract]. Neth J Med. 1998;52 ((suppl)) 25S
Briet  Evan der Meer  FJRosendaal  FRHouwing-Duistermaat  JJvan Houwelingen  HC Family history and inherited thrombophilia [letter]. Br J Haematol. 1995;89691
Link to Article
Kuo  LDavis  MJCannon  MSChilian  WM Pathophysiological consequences of atherosclerosis extend into the coronary microcirculation: restoration of endothelium-dependent responses by L-arginine. Circ Res. 1992;70465- 476
Link to Article

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Users' Guides to the Medical Literature
Back to the Clinical Scenario—Part 1