Implications of applying widely accepted cholesterol screening and management guidelines to a British adult population: cross sectional study of cardiovascular disease and risk factors

British Medical Journal, Oct 24, 1998 by Nigel Unwin, Richard Thomson, Ann Marie O'Byrne, Mike Laker, Heather Armstrong

Introduction

Considerable attention has been focused recently on promoting evidence based practice and the potential of guidelines to inform and support appropriate care and changes in clinical behaviour.(1-3] Guidelines have been drawn up on the prevention of coronary heart disease--in particular, on the screening and management of patients with lipid disorders. Guidance on the use of statins, based on the Sheffield table,[4] was recently circulated to all doctors in the United Kingdom.[5] There are important differences in the recommendations of the major guidelines, however, yet neither these differences nor the implications for clinical practice have been studied.

We have applied data from a population based survey to the different guidelines for a population aged 25-64 years.[6] We aimed to describe the potential implications of differences in commonly available and widely promoted guidelines produced by the British Hyperlipidaemia Association,[7] the British Drugs and Therapeutics Bulletin[8] the European Atherosclerosis Society,[9] and the American national cholesterol education program.[10]

Methods

Recruitment and data collection

The data used in this paper are from the Newcastle heart project--a population based study of coronary heart disease, diabetes, and associated risk factors in the general (predominantly of European origin), Chinese, and South Asian populations of Newcastle upon Tyne.[6] We have used data from the general population for this paper. This was a population based sample from the patient register of the Newcastle Family Health Services Authority, the list of all individuals in Newcastle registered with a general practitioner. We took an age and sex stratified random sample of those aged 25 to 64 years after removing any Chinese sounding names (less than 0.5% of the sample).[11]

Lipid analyses

Subjects were recruited to the study between April 1993 and November 1994. After overnight fasting, subjects' height and weight were measured, their body mass index (kg/[m.sup.2]) was computed, and a fasting blood sample was taken. Until May 1994 the lipid analyses were performed on a Cobas Bio centrifugal analyser (Roche Products Ltd., Welwyn Garden City) and after this date a DAX analyser was used (Bayer plc, Basingstoke). Throughout the study period, the laboratory participated in an external quality assurance scheme. This showed no changes in bias (inaccuracy) for cholesterol or high density lipoprotein cholesterol. However, the data for triglycerides confirmed that the DAX data showed a positive bias relative to the Cobas Bio data and therefore results obtained with the DAX were adjusted as previously described.[12] The low density lipoprotein cholesterol concentration was calculated using the Friedewald formula.[7]

Cardiovascular data

Subjects had two blood pressure measurements. These were made by trained observers using a standard mercury sphygmomanometer with an alternate size cuff.[13] A 12 lead electrocardiogram was recorded with the subjects at rest. The findings were coded according to the Minnesota manual by two independent observers; a third observer was used where the two disagreed.[14] Each subject completed a questionnaire, which included items on diabetes, hypertension, coronary heart disease, and stroke (all diagnosed by a doctor); smoking status; causes of death in any parents or siblings who had died; and the World Health Organisation questionnaire on intermittent claudication.[15] For women, the questionnaire also inquired about age at the time of the menopause, and any factors affecting its onset. Local ethical committee approval was received for the study and all subjects gave informed consent before participating.

Applying the guidelines

Space does not permit a detailed description of the guidelines. Here, we have focused on the people for whom the guidelines recommend intensive treatment in the form of rigorous dietary intervention under-pinned by professional dietetic advice, with or without drug treatment. Table 1 summarises how we applied each of the guidelines to the data. The European Atherosclerosis Society and national cholesterol education program guidelines specify two target levels for active intervention: one for drug treatment (if a trial of dietary intervention fails) and the other for intensive dietary intervention only. Table 2 gives the definitions of the different conditions and risk factors we used in applying the guidelines to the study population.

Table 1 Application of guidelines to data(*)

Population to be screened        Population to be treated

British Hyperlipidaemia
Association

In order of priority:            Presence of coronary heart
                                 disease and LDL cholesterol
                                 >3.4 mmol/l

Vascular disease                 Presence of [is greater than or
                                 equal to] 2 out of: diabetes,
                                 hypertension (1)(*), current
                                 smoker, or obesity and LDL
                                 cholesterol >5.0 mmol/l

Family history (1)(*)            Male sex and LDL cholesterol
of coronary                      >6.0 mmol/l
heart disease

Diabetes, hypertension           Female sex, postmenopausal,
(1)(*), current smoker,          and LDL cholesterol
or obesity                       >6.0 mmol/l

Drugs and Therapeutics
Bulletin

Vascular disease, or a           Presence of vascular disease
family history (1)(*)            and LDL cholesterol [is greater
of coronary heart                than or equal to] 3.4 mmol/l
disease; or

Particular combination           If no overt vascular disease,
of age, sex, hypertension        decision from table based
(1)(*), left ventricular         on combination of age, sex,
hypertrophy, smoking, and        diabetes, smoking,
diabetes from risk table         hypertension (1)(*), left
                                 ventricular hypertrophy,
                                 and total cholesterol value

European Atherosclerosis
Association

All                              Presence of vascular
                                 disease and total
                                 cholesterol >5 mmol/l
                                 (<6 mmol/l dietary
                                 therapy only)

                                 Coronary heart disease risk >20%
                                 over 10 years (determined by
                                 risk chart according to age,
                                 sex, smoking status, blood
                                 pressure, and total cholesterol)
                                 and total cholesterol
                                 >5 mmol/l (<7 mmol/l dietary
                                 therapy only)

                                 Coronary heart disease
                                 risk [is less than or
                                 equal to] 20% and total
                                 cholesterol >7 mmol/l
                                 (<8 mmol/l dietary
                                 therapy only)

National cholesterol
education programme

All                              Presence of coronary heart
                                 disease and LDL cholesterol
                                 [is greater than or equal to]
                                 2.6 mmol/l (<3.4 mmol/l
                                 dietary therapy only)

                                 LDL cholesterol [is greater
                                 than or equal to] 3.4 mmol/l
                                 (<4.1 mmol/l dietary therapy
                                 only) and presence of [is
                                 greater than or equal to] 2
                                 (3 if HDL cholesterol
                                 [is greater than or
                                 equal to] 1.6 mmol/l) out of:
                                 male, age [is greater than
                                 or equal to] 45, diabetes,
                                 hypertension (2)(*), current
                                 smoker, postmenopausal female,
                                 family history of coronary
                                 heart disease (2)(*), HDL
                                 cholesterol <0.9mmol/l

                                 LDL cholesterol [is greater
                                 than or equal to] 4.1 mmol/l
                                 (<4.9 mmol/l dietary
                                 therapy only) with
                                 <2 risk factors