Concomitant health conditions may have an impact on hyperlipidaemia patients’ CV risk category and, by extension, their LDL-C target. This is particularly true for CHD and other conditions that are classed as CHD risk equivalents because these are considered to be the highest risk indicators for CVD, and therefore have the most stringent LDL-C targets. The studies we reviewed showed considerable variability in LDL-C goal achievement for patients with different concomitant conditions (Additional file
1: Table S3). In the majority of the studies, more than 60 % of patients failed to achieve the LDL-C target levels. In a 4E-Registry study [
34], the percentage of male patients with diabetes mellitus failing to achieve goal levels was similar to the percentage of male patients without diabetes failing to achieve goal levels (74.7 % vs. 71.7 %). Women without diabetes mellitus, however, did much better in achieving their individual lipid goals: 55 % did not attain the goal levels, compared with 76 % of women with diabetes. However, achievement of treatment goals in patients with diabetes was just as poor as in other high-risk groups in the 4E cohort. In a cross-sectional survey conducted in Asia [
35], >70 % of patients with diabetes, CHD, carotid artery disease, peripheral arterial disease, metabolic syndrome, or other multiple risk factors (10-year CHD risk >20 %) did not achieve the recommended LDL-C targets.
Some studies observed that the number of patients with CHD who do not achieve their LDL-C targets was not as high (<50 %); but most studies reported that the majority of patients did not meet their targets. A similar trend was observed in patients with other concomitant conditions such as hypertension, stroke, and kidney disease. One common theme among the studies that compared concomitant conditions was that patients with multiple conditions (i.e., patients at higher CV risk) were less likely to reach LDL-C goals than patients with a single condition. Another notable theme was that, within an individual study, patients in higher CV risk categories were less likely to reach LDL-C target goals than patients in lower CV risk categories. However, it should be noted that patients in higher risk categories have lower target goal levels.
Potential reasons for patients not achieving target LDL-C levels
The reasons why patients did not achieve their LDL-C targets was not consistently investigated nor reported across the studies included in this review. Of the studies that did report reasons, only a few conducted univariate or multivariate analysis to investigate the relationship between patient-level factors that may have contributed to failure to reach targets. Patient characteristics such as gender; age; race; body mass index; and comorbid conditions such as diabetes, CHD, peripheral arterial disease, and carotid arterial disease are some of the known risk factors that influence the achievement of LDL-C target goals. However, it is difficult to reach any firm conclusions because some of the studies report conflicting evidence.
Two studies, one of which was a large international survey, reported that males were more likely to attain their LDL-C target goals than females [
36,
37], with a univariate analysis finding that being female decreased the odds of attaining the LDL-C goal (odds ratio = 0.62, 95 % CI, 0.39-0.99;
P = 0.043) [
36]. Contrary to these findings, two large studies reported that successful LDL-C goal attainment was positively associated with being female [
29,
38].
A Chinese study found that older age increased the odds (odds ratio = 1.02; 95 % CI, 1.00–1.05 for every 10 years increment in age;
P = 0.038) of attaining the LDL-C target goals [
36]. Older age was also found to be a multivariate predictor of successful LDL-C goal achievement in a worldwide multicenter study [
37]. Conversely, a large study in the US found that older age was negatively associated with LDL-C control [
38]. Similarly, another study reported that LDL-C goal attainment was significantly related to an age <40 years [
29].
As might be expected, several studies reported that baseline total cholesterol or LDL-C levels had an inverse relationship with LDL-C target achievement, i.e., higher baseline total cholesterol or LDL-C was associated with significantly lower odds of attaining LDL-C goals,
P <0.001 [
35,
36,
39]. Baseline CV risk was also found to influence attainment of LDL-C goals. Two studies conducted in Asia [
35,
39] suggested that goal attainment was inversely related to baseline CV risk, i.e., the higher the CV risk at baseline, the less likely the patients were to reach their target. These findings were supported by a large multicentre, international trial, which found that being in a lower risk CV group was a multivariate predictor of successful LDL-C goal achievement [
37].
Patient adherence has been considered to be a major factor in the low rate of LDL-C target attainment; higher adherence to treatment is linked to higher proportions of patients reaching their targets [
35]. Reasons for non-adherence were cited as patients forgetting to take their medication or stopping taking their medication when their cholesterol had returned to normal [
33,
35,
40]. A cross-sectional study in Brazil suggested that non-adherence was common in the population with scarce financial resources due to the high cost of medication [
30]. Improper communication between health care professionals and the patients, which was particularly clear among aged patients or those with poor literacy, was also found to be an important factor for non-adherence [
30].
Whilst current guidelines for treating hyperlipidaemia provide specific algorithms for the treatment of chronic conditions, they also present a more complex approach to lipid management, which requires physicians to make decisions about multiple options for treating each patient. A cross-sectional survey conducted in the United States [
41] showed that although a significant minority of patients did not receive a dose increase when one appeared warranted, approximately 70 % of patients did receive a dose increase at some point. There was a highly significant association of several physician attitudes and beliefs with the decision to increase the statin dose; physicians who believed that “statins are effective” were more likely to increase statin dose, whereas those who had an attitude that “close enough to goal is good enough” were less likely to switch or titrate to higher statin dose [
41]. Of the patients who received an increase in statin dose, 50 % were still not at goal and few were on the highest doses, suggesting that physicians are not “treating to goal” [
41].