A retrospective study of lipid testing in Dr David Starritt's practice confirmed that hyperlipidaemia can be managed effectvely in primary care


 

Tarland is a small village in anattractive part of rural Aberdeenshire. The official population of the village is 450, but the practice has 750 patients as it draws on farmland for miles around.

I first started to think about the measurement and treatment of hyperlipidaemia in earnest in 1997, and actively set about measuring lipid levels, mainly on an opportunistic basis, in 1998.

The practice is small and easily managed, so we were able to test a higher proportion of the population than we are ever likely to do again.

During 1998 the goalposts kept moving as we first tried to make use of the laboratory recommendations on the result sheets. Later in the year we started using the Sheffield Table and then a little later the New Zealand variant. The results presented below may therefore reflect altered decision making processes adopted during the year.

We set out to examine:

  • Who? Were we testing the right people?
  • Why? Although we wanted to screen the general population, we did not want to neglect those with proven coronary artery disease.
  • So what? Did we act consistently and appropriately with the results?

There was also the question of resources, both of drugs and testing, as a cost to the NHS: had we used them well? I have differentiated between first-ever tests and subsequent tests in an attempt to assess the usefulness of follow-up.

The results obtained cannot necessarily be extrapolated to general practice as a whole, but I hope at least that you will find it an interesting study.

Study is a rather grand word, perhaps, for what is essentially a retrospective examination of what we have been doing here.

 

The various risk tables suggest that there is more to be gained by treating those with increased risk. The tables have an upper age limit of 70 years, and although there is some evidence of benefit from treatment for those up to age 75, there is virtually none for those beyond this age.

The chart in Figure 1 (below) shows the age distribution of males and females who had a first test during 1998. It peaks at the 65-69 band for males and the 70-74 band for females, which is probably what we had hoped would happen. We managed to test 50% of the men in that age band during the year and 56% of the women.

Figure 1
who did we test? 1st tests

The next chart (Figure 2, below) shows who we did subsequent tests on and follows much the same pattern, except that for some unknown reason there seems to be a preponderance of subsequent testing in very elderly males. This is probably due to the small numbers involved, but also indicates some inappropriate testing.

Figure 2
who did we test? 2nd tests

The chart in Figure 3 (below) shows the percentage of the population on statins in the various age bands. Working on the basis that it is better to treat those who are at increased risk, this chart is very satisfactory as it indicates that the percentage treated goes up through the age bands and peaks at 65-69. At that age, 17% of men and 16% of women are being treated. If the criteria for treating were to be changed, this would have massive cost implications.

Figure 3
percentage of population on statins by age bands

 

A total of 151 tests were performed in 1998. Of these, 83 were first tests and 64 were subsequent tests (Figure 4).

Figure 4
% of1st tests and follow-ups: primary v.secondary prevention

In primary prevention, 70% of the tests were first-ever tests, whereas in secondary prevention 71% of the tests were follow-ups, indicating that, after initial testing, subsequent testing is weighted towards those in the secondary prevention group – which is appropriate (Figure 5).

Figure 5
lipid levels in primary prevention: 1st test v. follow-ups

We also looked at the lipid levels to which we were reacting (Figure 5). First tests in primary prevention reflect general screening, and subsequent tests would only be performed in those with a high total cholesterol or an adverse ratio. Figure 5 shows that in this group, for those who were followed up, despite the dietary advice which they must have received, results are not quite as good as in the general population.

If we look at the same sort of figures in relation to secondary prevention (Figure 6), you would expect to find a different picture. To start with, the results of the first tests are marginally worse than in primary prevention, but the main point is that, on follow-up, improvement has been found in all parameters – which is reassuring.

Figure 6
Lipid levels in secondary prevention: 1st tests v. follow-ups

 

The next chart (Figure 7) refers to primary prevention and separates first tests from follow-ups. It shows that more than 60% of tests in this group resulted in no change and only a very small number of patients were started on treatment. However, a significant number were given dietary advice after the first test.

Figure 7
What did we do with the results? Primary prevention

By contrast, in the secondary prevention group (Figure 8) only 29% of first tests resulted in no change, and subsequent testing proved much more valuable than in the primary prevention group.

Figure 8
What did we do with the results? Secondary prevention

The charts in Figures 9 and 10 illustrate the lipid levels at which the various interventions were introduced. Figure 9 relates to primary prevention and Figure 10 to secondary prevention. I think you will agree that the charts show that we have managed to intervene appropriately.

Figure 9
At what levelsÞprimary prevention, 1st tests
Figure 10
At what lipid levelsÞ secondary prevention, 1st tests

Finally, we looked at similar charts, but based on follow-up testing. In primary prevention (Figure 11) we failed to show that any logical decision making process was being used. We shall either have to think this through again, or abandon subsequent terting in primary prevention. Figure 12 shows that subsequent testing in secondary prevention was more worthwhile.

Figure 11
At what lipid levelsÞ primary prevention, follow-up tests
Figure 12
At what lipid levelsÞ secondary prevention, follow-up tests

This sort of exercise stimulates interest and generates enthusiasm to everyone's benefit. It also illustrates, to those who may doubt it, that hyperlipidaemia as a risk factor for cardiovascular disease can be appropriately managed in general practice.

  • Readers wishing to view the data on which these charts are based may obtain them by writing to the author at Tarland Medical Practice, Ailsa Muir, The Market Stance, Tarland, Aberdeenshire AB34 4UB, or contacting him by email: Starritt@bigfoot.com.

Guidelines in Practice, July 1999, Volume 2
© 1999 MGP Ltd
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