Understanding the scientific literature

(Reading and evaluation of a research paper)

Prof David LaneDepartment of Haematology

Hammersmith Hospital Campusd.lane@imperial.ac.uk

Our paper is:

Risk factors and recurrence rate of primary deep vein thrombosis of the upper extremities. Martinelli et al, Circulation 2004; 110: 566-570

(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

Prothrombin Thrombin

FVa

FX FXa

FVIIIa

FIXa

End Stage Blood Coagulation

TF/FVIIa

Coagulation Inhibitory Mechanisms

1. Antithrombin (+heparin or heparan sulphate)

2. Protein C anticoagulation pathway3. Tissue factor pathway inhibitor

1 & 2 are of know clinical importance!3 is important physiologically, but of uncertain

clinical importance!

+

+

FVIII

FV

Procoagulant

FibrinFibrinogen

Prothrombin Thrombin

FVa

FX FXa

FVIIIa

FIXa

Thrombin-Antithrombin Complex

FXa-AntithrombinComplex

Antithrombin+ Heparin or EC Heparan Sulphate

Anticoagulant

Anticoagulant

Coagulation Regulation By Antithrombin

+

+

FVIII

FV

FVIIIi

FVi

Procoagulant

Protein Ca(APC)

Protein C/EPCR

Protein S

Anticoagulant

ThrombomodulinFibrinFibrinogen

Prothrombin Thrombin

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

Arg306Arg306

“Slow” cleavage

Completely abolishesFVa activity

Arg506Arg506

“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 II XIV

Organisation of Prothrombin Genechromosome 11p11-q12

~21kb

20210 G/A,increases prothrombin levels, increase risk of

DVT

X

Catalytic domain

V VII

KringlesLeader + Gla

(Degan & Davie Biochemistry 26 6165, 1987 Poort et al Blood 88 3698 1997)

Some risk factors for venous thromboembolismGenetic (thrombophilia) risk factorsAntithrombin deficiency*Protein C deficiency*Protein S deficiency*Factor V Leiden*Prothrombin G20210A*

Acquired/acquired risk factorsHyperhomocysteinemia*Antiphospholipid antibodies

Transient risk factorsOral contraceptives*TravelSurgeryHRTPregnancy

*of interest today

Risk

Age

Thromboticthreshold

Risk from “ageing”

Genetic risk 2

Genetic risk 1

Venous Thrombosis is Multi-Causal Arising from Interacting Genetic

and Acquired Risk Factors

Cumulative riskTransient acquired risk

after Rosendaal, 1998

Odds RatioOdds of an event Number of events/number of non events

Odds ratioOdds in treated or exposed group/odds in

control group

Odds RatioIn a week

90/100 men have drunk beerOdds 90/10

20/100 women have drunk beerOdds 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 (1.6-7.0)

With 3.2 (0.8-12.3)(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 = 3.3522/775

(The adjusted results in last column are to be focussed on)

Example of OR calculation:

Compare results in last and first lines 5/35 = 9.093/191

(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 DVTin patients with compared to those without thrombophiliais 2.7 (95% CI 0.7-9.8): note this is not significant!

Task: In 60 minutes write a 250-350 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.