### INTRODUCTION

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^{5)}Thus, instead of measuring LDL-C levels directly, LDL-C concentration is usually estimated with Friedewald equation, using total cholesterol, triglyceride (TG), and high-density lipoprotein cholesterol (HDL-C) concentrations, in primary practice. This equation is known to be valid only in patients whose serum TG concentrations are less than 400 mg/dL.

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^{12)}It tended to overestimate LDL-C when TG was less than 150 mg/dL and underestimate it when TG was over 150 mg/dL. The use of Friedewald equation led to a 9.1% misclassification rate in those with higher TG levels versus an 8.3% misclassification rate in those with lower TG levels.

^{13)}Both overestimation and underestimation can be problematic; overestimating LDL-C leads to prescribing unnecessary medication and underestimating it can delay proper treatment. For this reason, many studies have attempted to modify the equation by changing the TG:VLDL-C ratio. A study conducted by DeLong et al.

^{14)}suggested an optimal TG:VLDL-C ratio of 6 instead of 5, using a large sample size of 10,483 individuals, and Puavilai et al.

^{15)}confirmed that this equation is more accurate than Friedewald's original equation, with an odds ratio of 2.63. Recently, Martin et al.

^{16)}suggested an adjustable novel factor instead of a fixed ratio, using the N-strata-specific median TG:VLDL-C ratio classified by TG and non-cholesterol level, which provided more accurate risk classification without additional costs as compared with Friedewald's original equation. Additionally, Lee et al.

^{17)}found that Martin's novel method significantly improved the LDL-C estimation when compared with Friedewald equation in the Korean population.

### METHODS

### 1. Study Subjects

### 2. Study Procedure

^{2}(kg/m

^{2}). Systolic and diastolic blood pressure (mm Hg) was measured by an automated oscillometric blood pressure recorder (Dinamap ProCare 100; GE Healthcare, Milwaukee, WI, USA), with the patients in a seated position after having them relax for five minutes.

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^{26)}Two of the equations used a different assumption of a TG:VLDL-C ratio, 4 and 6 instead of 5, and the Martin equation used a novel factor as described above. The Martin LDL-C (Martin equation, LDL-C

_{M}) estimate was calculated using an LDL-C calculator instead of the N-strata-specific median TG:VLDL-C ratio classified by TG and non-cholesterol level (http://www.ldlcalculator.com).

### 3. Statistical Analysis

### RESULTS

_{F}(Friedewald equation, 0.951), LDL-C

_{H}(Hatta equation, 0.917), LDL-C

_{P}(Puavilai equation, 0.968), and LDL-C

_{M}(0.983).

_{M}resulted in the best concordance with the direct measurement (86.1%) and LDL-C

_{P}resulted in the second-best concordance (82.5%) (Figure 1). LDL-C

_{F}resulted in a concordance of 79.5%, lower than that of LDL-C

_{M}and LDL-C

_{P}. LDL-C

_{P}had the highest rate of overestimation (9.9%); the overestimation using LDL-C

_{M}(5.4%) was similar to that using LDL-C

_{F}(5.8%). Conversely, LDL-C

_{P}had the lowest underestimation rate (7.5%), followed by LDL-C

_{M}(8.6%).

_{M}is appropriate for the majority of cases, 17% more using Delta% ≤5 and 13.1% more using Delta% ≤10, as compared with LDL-C

_{F}. LDL-C

_{P}was also superior to LDL-C

_{F}(7.3% and 6.8% more, respectively).

_{M}was found to produce the best approximate value of the 4 estimations, having a 5.5 mg/dL mean Diff and 5.1% mean Delta%. Meanwhile, LDL-C

_{F}resulted in a mean Diff of 8.2 mg/dL and a mean Delta% of 7.6%. LDL-C

_{P}also produced better results than LDL-C

_{F}, with a mean Diff of 7.0 mg/dL and a mean Delta% of 6.2%.

_{M}was shown to be less influenced by TG. The Diff and Delta% of LDL-C

_{F}were 5.5 mg/dL and 5.1%, respectively, when the mean TG level was below 100 mg/dL, but they increased drastically as TG increased and reached 18.5 mg/dL and 16.4% when TG was in the range of 200 to 399 mg/dL. The Diff and Delta% of LDL-C

_{M}increased gradually; they were 5.1 mg/dL and 4.9%, respectively, when TG was below 100 mg/dL and 7.1 mg/dL and 6.3% when the TG level was between 200 and 399 mg/dL.

_{F}and LDL-C

_{M}were not significantly different when HDL-C was high, but were significantly different when HDL was below 40 mg/dL.

### DISCUSSION

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^{25)}Recently, a new method using the N-strata-specific median TG:VLDL-C ratio was developed which uses TG and non-cholesterol level as the adjustable novel factors instead of a fixed ratio of 5.

^{16)}This method is reported to significantly improve LDL-C estimation when compared to Friedewald's equation in the Korean population.

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^{16)}and Lee et al.,

^{17)}who stated that the Martin equation offers a significant improvement in LDL-C estimation when compared with Friedewald equation. Our results show that the Martin equation is superior to Friedewald equation in that it produces the least difference and best concordance with directly measured LDL-C of the equations studied. Moreover, both the overestimation and underestimation rates are less than those produced by Friedewald equation; the difference is particularly pronounced in the underestimation rate. This is of particular importance because underestimation is generally considered riskier than overestimation, especially when screening the general population, as underestimation can cause delays in initial treatment. We found that the Martin equation is much less influenced by TG or by HDL-C than Friedewald equation.