Understanding the scientific literature (Reading and evaluation of a research paper) Prof David Lane Department of Haematology Hammersmith Hospital Campus

Our paper is: Risk factors and recurrence rate of primary deep vein thrombosis of the upper extremities. Martinelli et al, Circulation 2004; 110: (This is given to you initially without the Title and Abstract. The Abstract will be given out at the end)

Aims of the paper are: 1. Investigate the role of risk factors (thrombophilia, transient) in upper extremity DVT. 2. To evaluate recurrence rate after a period of antcoagulant therapy. It uses a case control study design.

Haemostasis is a fine balance between procoagulant and anticoagulant activities Inadequate procoagulant/excessive anticoagulant function - bleeding Lo Pro Coag Thrombosis Bleeding Hi Anti Coag

Haemostasis is a fine balance between procoagulant and anticoagulant activities Excessive procoagulant/inadequate anticoagulant function - thrombosis Hi Pro Coag Thrombosis Bleeding Lo Anti Coag

+ + FVIII FV Procoagulant FibrinFibrinogen ProthrombinThrombin FVa FX FXa FVIIIa FIXa End Stage Blood Coagulation TF/FVIIa

Coagulation Inhibitory Mechanisms 1.Antithrombin (+heparin or heparan sulphate) 2.Protein C anticoagulation pathway 3.Tissue factor pathway inhibitor 1 & 2 are of know clinical importance! 3 is important physiologically, but of uncertain clinical importance!

+ + FVIII FV Procoagulant FibrinFibrinogen ProthrombinThrombin FVa FX FXa FVIIIa FIXa Thrombin-Antithrombin Complex FXa-Antithrombin Complex Antithrombin + Heparin or EC Heparan Sulphate Anticoagulant Coagulation Regulation By Antithrombin

+ + FVIII FV FVIIIi FVi Procoagulant Protein Ca (APC) Protein C/EPCR Protein S Anticoagulant Thrombomodulin FibrinFibrinogen ProthrombinThrombin FVa FX FXa FVIIIa FIXa Coagulation Regulation by Activated Protein C

Factor Va Model of factor Va Pellequer et al Thromb Haemost 2000;84,849 APC cleavage sites in FVa

Inactivation of Factor Va By APC BIPHASIC INACTIVATION Arg306 “Slow” cleavage Completely abolishes FVa activity Arg506 “Rapid” cleavage Results in FVa with intermediate (25%-40%) co-factor activity

Factor V Leiden (Arg506Gln) FV Leiden (Arg506Gln) -mutation/polymorhism present in ~5% of white Caucasians -associated with “APC-resistance” -most prevalent genetic thrombophiliac factor in people of European descent Arg506Gln Arg->Gln substitution prevents proteolysis by APC at 506 site. FVa is therefore only partially inactivated

5’3’ I IIXIV Organisation of Prothrombin Gene chromosome 11p11-q12 ~21kb G/A, increases prothrombin levels, increase risk of DVT X Catalytic domain VVII Kringles Leader + Gla (Degan & Davie Biochemistry , 1987 Poort et al Blood )

Some risk factors for venous thromboembolism Genetic (thrombophilia) risk factors Antithrombin deficiency* Protein C deficiency* Protein S deficiency* Factor V Leiden* Prothrombin G20210A* Acquired/acquired risk factors Hyperhomocysteinemia* Antiphospholipid antibodies Transient risk factors Oral contraceptives* Travel Surgery HRT Pregnancy *of interest today

Risk Age Thrombotic threshold Risk from “ageing” Genetic risk 2 Genetic risk 1 Venous Thrombosis is Multi-Causal Arising from Interacting Genetic and Acquired Risk Factors Cumulative risk Transient acquired risk after Rosendaal, 1998

Odds Ratio Odds of an event Number of events/number of non events Odds ratio Odds in treated or exposed group/odds in control group

Odds Ratio In a week 90/100 men have drunk beer Odds 90/10 20/100 women have drunk beer Odds 20/80 Odds Ratio 90/10 = 36 20/80

95% Confidence Interval (CI) A 95% confidence interval is an interval generated by a process that is correct 95% of the time. It gives a measure of confidence to the mean. If 95% CI crosses unity, result not “statistically” significant! Compare OR (95% CI) 3.3 ( ) With3.2 ( ) (taken from Table 1 of paper)

Relative risk is another common measure of risk. RR= Probability of event in exposed group Probability of event in non exposed group RR is actually very similar to Odds Ratio, especially when the probabilities are small. In Clinical Studies, the Odds Ratio is favoured for case control studies and retrospective studies. Relative Risk is used in randomised controlled trials and cohort studies. Relative Risk

Example of OR calculation: Factor V Leiden 10/105= /775 (The adjusted results in last column are to be focussed on)

Example of OR calculation: Compare results in last and first lines 5/35= /191 (Results in final column, adjusted for age, are the ones to focus on)

Kaplan Meier plots and Hazard Ratios Kaplan Meier plots show survival (often expressed as % or as fraction of 1.00) over time Hazard ratio is broadly similar to Relative Risk. It is useful when the risk varies over time. The term is often used in connection with the Kaplan Meier survival plot (over time). If the overall RR of an event is half in one group, then HR is 0.5.

Prob of no recurrence at 5 years: Without thrombophilia 93% With thrombophilia 80% The adjusted Hazard Ratio for recurrence of upper limb DVT in patients with compared to those without thrombophilia is 2.7 (95% CI ): note this is not significant!

Task: In 60 minutes write a word abstract of the article. Divide the article into the following sections (section headings not to be included in the word count): Background Methods & Participants Results Conclusions Execution: Include size of study in Methods, and important findings in Results, expressed in quantitative terms.