Introduction
Low-density lipoprotein cholesterol (LDL-C) and non-high-density lipoprotein cholesterol (non-HDL-C) are the major risk factors contributing to the development of atherosclerotic cardiovascular disease (ASCVD), which can ultimately result in premature disability and mortality. An epidemiological study quantifying the association between exposure to LDL-C and ASCVD translated a lifetime cumulative exposure to LDL-C of 5000 mg-year, to an all-age ASCVD risk of 1%. Concerningly, this exposure–event relationship showed a logarithmic–linear association, resulting in a doubling of the risk every 1250 mg-year.1 The proportion of cases of ASCVD potentially prevented from LDL-C reduction was initially explored in the meta-analysis of randomised controlled intervention of statins in advanced age. The research found a relative risk reduction of 22% (adjusted risk ratio (aRR) 0.78, 95% CI 0.76 to 0.80).2 However, a Mendelian randomisation study investigating favourable genetic LDL-C single-nucleotide polymorphisms, which by implication confer a lifetime of lower LDL-C exposure, demonstrated a substantially larger relative risk reduction of 54% (aRR 0.46, 95% CI 0.41 to 0.52).3 4 In a recent prospective childhood to middle adult cohort study, it was found that both elevated LDL-C and non-HDL-C were independently associated with ASCVD (adjusted HR 1.35, 95% CI 1.13 to 1.60 and 1.94, 95% CI 1.23 to 3.06, respectively). The difference in ASCVD occurrence in both cases of lipid profile abnormalities can be attributed to exposure–time interaction. In summary, the risk period for the development of ASCVD needs to be minimised by earlier life course detection and intervention in cases with elevated LDL-C and non-HDL-C.5
The 2019 American College of Cardiology and American Heart Association guidelines regarding the primary prevention of cardiovascular disease emphasised control of lifelong ASCVD risk factors, including hyperlipidaemia. In young adults aged 20–39 years, discussions on treatment should be initiated at LDL-C ≥160 mg/dL or non-HDL-C ≥190 mg/dL and definitive treatment in suspected cases of familial hypercholesterolaemia with LDL-C ≥190 mg/dL.6 Nevertheless, access to lipid screening remains suboptimal in young adult sociodemographic groups in both countries, with 44.1% of American and 94.6% of Thai young adult cases unaware of their elevated LDL-C levels.7 8
Diagnostic prediction studies offer a potential strategy to enhance screening access for elevated LDL-C cases across countries in the low-income to middle-income group with limited resources as a major constraint.9–13 Regression-based statistical models with anthropometric, demographic and biological impedance predictors have been developed to detect the occurrence of dyslipidaemia,9 10 12 13 or specifically elevated LDL-C,11 using determinants include age,9–13 gender,9–13 family history,10 13 (diabetes,10 hypertension,10 cerebrovascular disease,10 dyslipidaemia13), education level,9 11–13 income,9 12 13 marital status,9–13 exercise,9–13 occupation,9 13 occupational risk factors,13 body mass index (BMI),10 11 waist circumference,9–11 body fat percentage,10 11 vital signs (systolic blood pressure (SBP),10 diastolic blood pressure (DBP),10 pulse10), smoking,10–13 drinking10 13 and personal underlying diseases (diabetes,12 heart disease12 and hypertension13). The limitations proposed by these prediction models can be summarised into three aspects. First, the source population consisted of elderly, rural populations, whereas contemporary concepts require detection of cases at an early age to prevent the progression of atherosclerotic plaque and residual ASCVD risk.6 Second, the prediction models had been constructed on different diagnostic endpoint definitions. Four out of five models focused on dyslipidaemia9 10 12 13 as a composite diagnostic endpoint of low HDL-C, elevated LDL-C, elevated triglyceride levels (TG) and elevated total cholesterol (TC). Nevertheless, current practice guidelines6 need a different therapeutic agent for each of the lipid type abnormality, thereby limiting applicability of these models. Third, different thresholds of elevated LDL-C were used, specifically ≥130 mg/dL,11 ≥160 mg/dL and ≥240 mg/dL.9 10 13 This leads to limited generalisability of the model to other countries with different clinical practice guidelines. Fourth, the prediction models have limited performance according to the area under the receiver-operating curve (AuROC) of 0.69–0.74.9–13 Finally, since direct LDL-C measurement is limited to only a few secondary to tertiary care centres, for the Thai guidelines on dyslipidaemia a surrogate marker, non-HDL-C, was used as an alternative measurement of lipid profile. As a consequence of these limitations this study aimed to develop and internally validate the model on specific lipid types: LDL-C and its surrogate marker, non-HDL-C, in a source population of young Thai adults, in order to increase the use of preventative screening for public and occupational health purposes.