How Long After Change In Diet To Retake Cholesterol Test
Br J Gen Pract. 2011 Feb i; 61(583): e81–e88.
The rise of cholesterol testing: how much is unnecessary
Helen Doll, BSc, MSc, DPhil, senior medical statistician
Brian Smooth, MD, FRCPath, consultant chemical pathologist, Jonathan Kay, MA, MSc, MB, BS, FRCPath, consultant chemic pathologist, and Tim James, BSc, MSc, PhD, FIBMS, head biomedical scientist
Department of Clinical Biochemistry, Oxford Radcliffe Hospitals NHS Trust, Oxford
Paul Glasziou, FRACGP, MRCGP, PhD, professor of prove-based medicine
Section of Master Health Care, University of Oxford
Received 2009 Nov 27; Revised 2010 Jan 18; Accepted 2010 May 25.
Abstract
Groundwork
Laboratory testing has increased dramatically over recent decades, which is a consequence peculiarly of echo testing or monitoring, equally either a response to treatment or follow-up.
Aim
To assess rates of measurement of lipid levels (total cholesterol, loftier-density lipoprotein, triglyceride) for diagnosis and monitoring over the last 20 years.
Design of study
Inspect of electronic database.
Setting
A unmarried region in the Great britain (Oxfordshire).
Method
Specimens from individual patients were matched over fourth dimension. All tests that were the third or more in a 3-year menses were considered to exist for monitoring, while the offset and second were considered to be for diagnosis. As recent show-based recommendations propose that frequent monitoring of cholesterol may reflect measurement error rather than true changes, between 1 and three tests in each 3-yr menstruum were considered to exist 'necessary'.
Results
Over the 20 years from 1987 at that place has been a more than than 15-fold rise in the overall number of lipid tests requested. After a pocket-size turn down in the early 1990s, testing rose steadily after publication of several large statin trials, particularly tests requested in chief rather than secondary care. Repeat testing (likely to be for monitoring) rose from 24% of tests (1993–1995) to 61% (2005–2007), with between 42% and 79% of tests in 2005–2007 possibly beingness unnecessary. Mean cholesterol values declined over time from 1996 onwards.
Decision
In the last decade, the number of cholesterol tests performed in Oxfordshire has risen dramatically. Much of this appears to be for monitoring purposes rather than example finding or chance cess. The majority of cholesterol tests requested may be unnecessary.
Keywords: cholesterol, laboratories, hospital, patient monitoring, testing, lipid, statin
INTRODUCTION
The utilize of laboratory tests has increased dramatically over the final decades. While some of this increase has provided clinical benefits, some also reflects inappropriate examination ordering.1 – 4 Repeat testing is a major, and growing, component of all laboratory testing,v with at least some likely to exist unnecessary.vi Although the repeat testing may be for relatively simple tests, the high book of such tests makes the issue important.
Lipid measurement is essential for calculating an individual's overall risk of coronary centre affliction (CHD):seven , 8 loftier total cholesterol,9 high low-density lipoprotein (LDL),10 and depression high-density lipoprotein (HDL)xi cholesterol are associated with increased take chances. The risk-prediction charts of the Joint British Societies use full cholesterol or the total-to-HDL cholesterol ratio,7 making these the virtually usually measured blood lipids. LDL may be measured direct, but is more unremarkably calculated using the Friedewald formula, which requires triglyceride measurement.12
Introduced in 1987, statins (or 'HMG-CoA reductase inhibitors') have made a dramatic difference to lipid direction, being particularly effective in reducing LDL cholesterol.13 Cholesterol lowering using statins reduces CHD bloodshed among those at both moderate and high run a risk of CHD,xiv – 21 with moderate chance defined as 15–xxx% and loftier risk as ≥30% for a ten-twelvemonth CHD event.vii , 22
The number of statin prescriptions has grown by xxx% annually, with UK statin expenditure increasing from around £20 million in 1993 to over £113 million in 1997,18 and to £700 million in 2004, representing 9.1% of prescription costs of the National Health Service (NHS).23 Atorvastatin and simvastatin stand for the peak two drug costs in England (£360 and £251 million respectively).24 National Institute for Health and Clinical Excellence 2006 guidelines advise the employ of statins for both primary and secondary prevention of CHD, stating that the statin with the lowest conquering costs should be used.25 The annual NHS bill for statins was predicted to take been more than £2 billion in 2010.23
Whether the rise in statin usage has been paralleled past a rising in cholesterol testing and monitoring has non been systematically studied. Cholesterol tests account for about two.5% of all biochemical tests, and treatment guidelines recommend at least annual monitoring of lipid levels for patients on lipid-lowering therapy.26 However, it has been suggested that, because of the weak signal-to-noise ratio in measuring cholesterol level, frequent monitoring of cholesterol might reflect measurement error rather than true changes,6 and less frequent testing of cholesterol, such as every three to 5 years, might be warranted in compliant patients who have reached their target levels: it took nearly 4 years for long-term variation to exceed short-term variation.six Results were like in plain healthy patients not taking cholesterol-lowering medication.27 This implies that testing of both at-target treated and good for you non-treated patients more than once every 3 years may exist unnecessary.
This written report examined the patterns of cholesterol testing within Oxfordshire, Uk, over a 20-year period from 1987 to 2007. This study aimed to: (1) written report the change in the number of cholesterol tests during the 20-year flow by source (master or secondary care) and patient demographics (age, sexual activity); (2) calculate the number of tests by 3-yr period and estimate the proportion of tests for monitoring rather than diagnosis, and the proportion that may be unnecessary; and (3) relate frequency of testing to estimated changes in hateful cholesterol levels.
METHOD
The Department of Clinical Biochemistry at the Oxford Radcliffe Hospitals NHS Trust serves the population of Oxfordshire and parts of several neighbouring counties (master and secondary care), likewise as third care for several counties. The service is provided through laboratories within the John Radcliffe and Churchill hospitals in Oxford and the Horton Hospital in Banbury. The Department performs more than v.seven meg tests a yr, and has an 'Chiliad'-based laboratory information management system with complete data going back to the mid-1980s. The standard laboratory practice throughout the period was to undertake all of, and but, those tests ordered by the requesting clinician.
The laboratory information management system was searched for all total cholesterol, HDL cholesterol, and triglyceride measurements over the period from 1987 to 2007. For each specimen, the patient'due south hospital or NHS number (where known), and their surname, forename, sex, date of birth, the date of the specimen, the requesting md, and his/her location were too recorded. As consultant head of the Department of Clinical Biochemistry, one of the researchers has full access to the data; no one outside the department was given access to data that were not fully anonymised or aggregated.
The NHS number was used to link records. For the 5% of records overall with no NHS number (the proportion was greater in earlier years), patients' surname, forename, sexual practice, and date of birth were used to friction match with those already linked using NHS numbers. Data were and then anonymised. For each patient, the dates of the first and last specimens, and the number of specimens in each year were determined. Information were so considered in 3-year periods. While the purpose of tests (screening or monitoring) was not recorded, in each three-year period all tests beyond the 2d (3rd and subsequent specimens) were considered likely to exist for monitoring rather than diagnosis: either as a response to treatment or for longer-term follow-upwards.
Similarly, it was non known which patients were being treated and, of these, which were at target. A sensitivity assay was used to estimate a range of possible values for the proportion of unnecessary tests, assuming that only the start test in each 3-year menstruum may be necessary for patients, both treated and untreated, who are at target6 , 27 while for those patients who accept yet to attain target levels, more than frequent (for example, annual26) testing may be warranted. The proportion of unnecessary tests was thus estimated to prevarication between the fourth or more than (that is, those tests that were more frequent than almanac) to the second or subsequent tests in each iii-year menstruation. Equally the individuals in the sample volition take comprised both those who were at target and those who were non, the true value, based on electric current evidence-based recommendations, is likely to lie within this range.
Statistical methods
Data were analysed using R.28 To appraise factors related to cholesterol level, a series of maximum likelihood mixed effects linear regression models were fitted to the data.29 These models permit for correlation between repeated measurements and for both fixed and random effects. Person ID was fitted as a random effect; fixed furnishings included sexual practice, age, and age-squared (to allow for the observed non-linearity of the relationship between age and cholesterol), time since first test, specimen number, testing period (upwardly to 1995 versus afterward 1995), and the interaction between specimen number and testing period.
RESULTS
Over the two decades, the number of full cholesterol requests per year increased more than 10-fold from 10 193 in 1987, to 117 488 in 2007 (Figure i). During the early on 1990s there was a slight fall in the number of total cholesterol tests requested, followed by a rapid iv-fold rise from 1996 onwards. The largest absolute increases in specimen requests occurred during 2003 (eleven 305 tests) and 2004 (15 888 tests). The increase in triglyceride requests was like (7180 in 1987 to 85 885 in 2007; an almost xi-fold increment), but much greater for HDL cholesterol (9 tests in 1987, and 1081 in 1995, to 88 356 in 2007; an 81-fold increase from 1996 onwards; Figure ii).
Number of total cholesterol tests requested from 1987 to 2007 in Oxfordshire, UK and dates of key guidelines and statin trial publications. QOF = Quality and Outcomes Framework.
Number of total cholesterol, triglyceride, and loftier-density lipoprotein (HDL) cholesterol tests requested per year by primary care (open bar areas) and secondary care (shaded bar areas).
Over all analyses, the increase to 291 729 tests in 2007 was nigh 16-fold from 1987 (17 382 tests) and more than 7-fold from 1996 onwards (35 988 tests in 1995). Within each historic period group, the number of specimens more often than not increased over fourth dimension. However, the increase was smallest in those anile <xxx years (7953 specimens requested in 1987–1989 versus 30 256 in 2005–2007; a relative increase of almost three-fold) and greatest in patients in their seventh (8580 versus 84 186; relative increase almost ix-fold) and eighth decades (3095 versus 77 794; 24-fold).
For all three analyses, virtually of the increment in requests originated from requests made in primary rather than secondary care: 28-fold versus 1.8-fold for total cholesterol, 26-fold versus ane.9-fold for triglycerides (both 1987 to 2007), and 223-fold versus 81-fold for HDL (1992 to 2007) respectively (Figure ii). The proportion of specimens from females increased from forty% to 50% over this 20-year menses.
Tests per person
Of 355 517 individuals identified, the number having a first recorded cholesterol examination per three-twelvemonth period increased from 25 538 in 1987–1989 to a tiptop of 77 465 in 2002–2004. The median age at fourth dimension of first specimen and proportion of females increased from 52 years and 44% in 1987–1989, to 60 years and 49% in 2005–2007. Figure three shows the overall numbers of tests, and numbers of tests per person, performed over each 3-year period. The acme of each bar corresponds to the overall number of tests performed, with each bar broken downwards past the proportion of each number of tests per person within that period (one to six and more tests).
Total number of tests performed per 3-year flow, broken downward within each bar by frequency of testing (1, 2, 3, four, 5, ≥6 tests per person: the darker the shading the greater the test frequency). Tests performed on a full of 355 517 individuals.
In 1987–1989, 19 666 people (77% of the total number of people) had i exam, approximately half (53%) of the total number of tests (36 973) performed during these 3 years (Table 1). While the proportion of people with ane test decreased to 48% in 2005–2007 (21% of 342 774 tests), the overall number of individuals having one test increased to 73 031. At the same fourth dimension, the proportion of those having five or more tests increased from 2.iii% in 1987–1989 (597 individuals having 4346 tests) to 9.nine% in 2005–2007 (fifteen 151 individuals having 93 757 tests). The tests requested in these 9.9% of individuals deemed for 27% of all tests during this last 3-year menstruum.
Table 1
Number (%) of specimens from all 355 517 patients having the specified number of tests per 3-twelvemonth period.a
| 3-yr catamenia | Diagnosis | Monitoring | Full | Sensitivity analysis of unnecessary testing | ||
|---|---|---|---|---|---|---|
| | ||||||
| one test | 2 tests | ≥3 tests | All tests | Lower jump ≥ii tests | Upper bound ≥4 tests | |
| 1987–1989 | xix 666 (53) | 6788 (18) | 10 519 (28) | 36 973 | 17 307 (47) | 6466 (17) |
| | ||||||
| 1990–1992 | 31 870 (49) | 11 658 (xviii) | 20 869 (32) | 64 397 | 32 527 (51) | 13 201 (twenty) |
| | ||||||
| 1993–1995 | 36 608 (57) | 12 734 (20) | 15 270 (24) | 64 612 | 28 004 (43) | 8373 (xiii) |
| | ||||||
| 1996–1998 | 48 524 (43) | 20 794 (18) | 43 579 (39) | 112 897 | 64 373 (57) | 29 362 (26) |
| | ||||||
| 1999–2001 | 65 298 (37) | 32 890 (19) | 77 369 (44) | 175 557 | 110 259 (63) | 53 678 (31) |
| | ||||||
| 2002–2004 | 76 548 (28) | 52 248 (19) | 140 785 (52) | 269 581 | 193 033 (72) | 96 352 (36) |
| | ||||||
| 2005–2007 | 73 031 (21) | 59 780 (17) | 209 963 (61) | 342 774 | 269 743 (79) | 143 417 (42) |
Monitoring versus diagnosis
The number and percentage of tests likely to be for monitoring (three or more tests) or diagnosis (one or two tests) inside each iii-year period are shown in Tabular array ane and Effigy 3. Between 1987 and 1989, 12% of patients had three or more than tests (31% of tests). This proportion stayed relatively constant, or fifty-fifty decreased slightly to 24% in 1993–1995, until 1996–1998 when it began to increase, with 44% of the tests in 1999–2001 and 61% of the tests in 2005–2007 existence for monitoring.
Necessary versus unnecessary tests
The proportion of tests in this dataset that were potentially unnecessary ranged from 17% (≥4th test) to 47% (≥2nd test) in 1987–1989, fell in 1993–1995 to 13–43%, and rose to 42–79% in 2005–2007, which represents between 143 417 and 269 743 unnecessary tests during the last iii-year menses (Table ane).
Changes in mean cholesterol
Mean cholesterol levels fell over the period from half dozen–7 mmol/50 in 1987 to around five.0 mmol/l in 2007. The levels had a non-linear relationship with age, with the values peaking at 60–69 years. Figure 4 shows the mean total serum cholesterol values and standard departure bars stratified by number of tests and 3-year period. Mean cholesterol levels are generally higher in those having more than tests before 1999–2001, and lower afterwards this. The solid line in Figure 4 shows the hateful cholesterol level over the 3-year periods for those being tested for diagnosis only (i or two tests per flow), while the dotted line shows levels for those whose tests were assumed to be for monitoring. Levels associated with monitoring decreasing markedly over time, reaching lower values than those for the accompanying diagnostic tests during 2005–2007. Hateful cholesterol levels at each exam for patients with increasing numbers of specimens inside each 3-year period are shown in Effigy 5. Mean values generally decrease with each additional test in each 3-year menstruum, and in all just the later years are higher the greater the overall number of tests requested.
Mean total serum cholesterol levels, with standard deviation (SD) bars, for individuals with i to half-dozen or more tests during each 3-year period. Overall mean values are shown for those tested for diagnosis (i or ii tests per menses; solid line joining circles) and for those tested for monitoring purposes (3 or more tests per flow; dotted line joining triangles).
Hateful full serum cholesterol levels at each test for patients with one (circle) to six or more tests (subsequent test values joined by a solid line) during each 3-year period. The 6 lines in each graph stand for the number of tests during each 3-yr period.
The mixed models showed that cholesterol was associated with sex (mean levels in males were 0.53 mm/l lower), age (patients in middle age more often than not having college cholesterol levels: every twelvemonth of historic period increased cholesterol past a hateful of 0.103 mmol/l, with the non-linearity of the age effect indicated by every historic period-squared decreasing the cholesterol level by a hateful of 0.001 mmol/50), number of specimens (with every extra specimen per three-yr menstruum increasing the cholesterol by a mean of 0.011 mmol/50), period of testing (cholesterol levels lower subsequently 1995, by a mean of 0.77 mmol/l), and time since kickoff test (cholesterol decreased by a mean of 0.086 mmol/l every year). Because of the large sample size, each estimate is precise and highly statistically meaning (P<0.0001).
The irresolute design of the relationship between specimen number and mean cholesterol in the later compared with the earlier periods (Figures 4 and 5) was shown past a significant interaction term between specimen number and period, which indicated that later 1995 each boosted specimen was associated with a mean reduction in cholesterol of 0.02 mmol/50. This is an overall outcome; the reduction is greater in later periods (Effigy 4). The hateful overall decrease of 0.49 mmol/fifty associated with specimens nerveless after 1995 remained, together with the overall human relationship between number of specimens and cholesterol values (every extra specimen was associated with a mean increase in cholesterol of 0.03 mmol/fifty).
DISCUSSION
Summary of master findings
The number of cholesterol tests (full cholesterol, triglycerides, and HDL cholesterol) performed in Oxfordshire savage briefly and so rose dramatically over the by xx years, with a more than 15-fold increase overall and a 7-fold increment over the concluding decade. The autumn and rise announced to follow closely the publication of systematic reviews, trials, and guidelines. Most of the increase is associated with requests made by main rather than secondary care, from an increase in testing of older rather than younger patients, and from an increase in the number of tests for monitoring purposes rather than case finding or cardiovascular disease take chances assessment. Over the last ii decades, the estimated proportion of tests for monitoring has more than than doubled from 28% to 61%. Similarly, the proportion of all tests in this dataset that are potentially unnecessary was estimated to be betwixt 17% and 47% in 1987–1989, ascent to between 42% and 79% in 2005–2007. Mean blood cholesterol levels decreased overall from six.3 mmol/l in 1987–1989 to 5.0 mmol/l in 2005–2007.
Strengths and limitations of the study
The strengths of the written report include the single electronic database with records of laboratory tests conducted in virtually of Oxfordshire (and surrounding counties for tertiary care) going back to the mid-1980s. The loftier proportion of patients who could be identified reliably using their NHS numbers immune patient data to exist linked over time, estimation of the proportion of tests during each 3-year period conducted for monitoring rather than diagnostic purposes, and, based on recent show-based recommendations,half dozen , 27 the proportion of tests that may have been unnecessary.
The study has some limitations. Outset, patient identification was imperfect: in earlier years in particular it relied on name, sex activity, and date of birth. Second, the use of frequency of testing to determine which specimens were obtained for monitoring and which were obtained for diagnosis is subject to error. While the employ of proper name, sex activity, and date of nascency to lucifer patient records with no NHS numbers means that the repeat charge per unit may take been underestimated because of failure to lucifer people with slightly unlike spellings of names or extra given names (for Ann versus Ann Margaret), equally, some tests may take been repeated for reasons such as the lack of a fasting blood sample, patient movement betwixt practices, or, for patients admitted to secondary intendance, repeat of a test already undertaken in primary care. Third, there was no information about the patients' histories and risk factors, and it is not known which patients were on handling and whether or not their target level of cholesterol was reached. Thus, it is not possible to suit for these factors, all of which would influence monitoring intensity. Fourth, a change in the scale of the testing around 1993 led to an artificial fall in reported cholesterol levels.30 5th, these data represent just the specimens requested by GPs and hospitals within the region and exercise not represent population values for Oxfordshire. Sixth, in that location is no data on cholesterol measurements undertaken in other laboratories, or with point-of-care devices, or of their contribution to changes in laboratory activity.
Comparison with existing literature
The small-scale fall in the number of cholesterol tests in the early 1990s followed past the rapid ascension in the late 1990s coincides with periodical publications and the advent of statin handling (Effigy 1). The autumn appears to reverberate the questioning of cholesterol treatments, notably the telephone call for a moratorium on cholesterol treatment published by the British Medical Periodical. 31 , 32 At that time, no clinical trial convincingly showed that reducing cholesterol levels decreases mortality, with many clinical trials33 and, particularly, observational studies,34 reporting associated increases in not-cardiac mortality. Fifty-fifty though studies such as the Framingham Study,35 the Multiple Risk Factor Intervention Trial, and the World Wellness Organization European Collaborative trial36 demonstrated the link between loftier blood cholesterol and CHD, and specific migrant studies showed the effect of environmental change in raising cholesterol levels with associated higher rates of CHD,37 the high prevalence of raised cholesterol levels suggested to some that such levels were biologically normal.38
The rise in testing appears to follow the publication of three clinical trials in the mid-1990s, with an initial slight increment following the 1994 publication of the Scandinavian Simvasatin Survival Study,fourteen the first trial to show that a statin could better survival in CHD patients. Further rises occurred afterward the 1995 publication of the West of Scotland Coronary Prevention studyfifteen — the get-go trial to prove effectiveness in the primary prevention of CHD among those with high cholesterol levels — and the 1996 Cholesterol and Recurrent Events trial,22 which showed beneficial effects in those with CHD and moderate cholesterol levels. The ascent in testing continued with the Joint British Societies' guidelines in 1998,seven the UK National Service Framework for CHD in 2000,39 and the publication of other trials such equally the 1998 Long-Term Intervention with Pravastatin in Lipid Disease trial,16 and the 2002 and 2003 publications from the Medical Enquiry Council/British Heart Foundation Eye Protection Study,20 , 21 together with the UK expiry of the simvasatin patent in May 2003.
The especially high relative increase in the number of HDL cholesterol tests requested (Figure 2) may reverberate the apply of the total-to-HDL cholesterol ratio as the risk-prediction tool in the 1998 Joint British Societies' guidelines,7 which first appeared as an appendix in the British National Formulary in 2000. The introduction of the Quality and Outcomes Framework (QOF) in April 2004, and its adjustment in April 2006, appeared to precede a slowing of the increase in cholesterol testing and its reduction, respectively.
Mean blood cholesterol levels in 2005–2007 were slightly lower than the published 2006 mean blood cholesterol levels for males and females anile xvi years and over in the whole of England (5.3 and 5.4 mmol/fifty),8 , 40 which probably reflects a regional effect.8 The levels are, nevertheless, close to those suggested past the National Service Framework for CHD of a cholesterol target of <5.0 mmol/l for both master and secondary prevention of CHD.39 More recent guidelines suggest a target for total cholesterol of <4.0 mmol/l for high-run a risk individuals.41
Implications for future enquiry and clinical exercise
Patients who practice not comply with treatment regimes constitute around 25% of those prescribed statins in primary care,42 and up to 85% of those who have received more than than 5 years of therapy.43 Regular checks can be used to monitor and enhance compliance as well equally assess the success of the prescribed therapy,41 and associated lifestyle interventions, such as dietary modification and increased exercise.44 While any reduction in frequency would need to exist undertaken in the context of associated patient-centred prevention strategies,45 the large proportion of tests for monitoring estimated to have been conducted in recent years is likely to reflect electric current treatment guidelines which recommend frequent monitoring of lipid levels for patients on lipid-lowering therapy.26 This frequency has recently been questioned using information from large treatment trials,6 , 27 although these observations have notwithstanding to touch on treatment guidelines. While the QOF requirement for patients on 'at risk' registers to have one almanac cholesterol exam may exist a barrier to evidence-based modify in practise, there is some evidence from this report that the QOF curtailed the rapid increase in cholesterol testing.
There appears to be considerable over-monitoring that may not benefit patients, while also straining laboratories and incurring considerable economic costs to the NHS and personal costs to patients. The electric current NHS organisation, whereby the local main care trust pays laboratories for testing on behalf of their practices, and where most of the tests are done under a block contract that just partially reflects action, does not necessarily encourage GPs to limit their use of this resources. The ascension over the last two decades in the proportion of tests for monitoring, combined with the estimated large proportion of all tests that may be unnecessary, advise there may be scope in some stable patients to reduce the volume of lipid testing, with potential benefits for the NHS, laboratories, and clinicians, and, moreover, for the individual patients.
Acknowledgments
Our thanks to Rod Jackson, David Mant, Dan Lasserson, Andrew Neil, and Jeffrey Aronson for helpful comments on drafts and analyses during the grooming of this paper.
Notes
Funding body
This work was supported a National Institute for Health Research Programme Grant.
Ideals committee
The National Research Ideals Service confirmed that the study was service inspect and therefore did not require upstanding approval.
Competing interests
The authors have stated that there are none.
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Articles from The British Periodical of General Do are provided here courtesy of Regal Higher of General Practitioners
Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3026174/
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