For the group as a whole, the greatest area under the ROC curve as a marker of total and total small, medium small, and very small LDL particle concentrations was a TG/HDL cut-point of 3 (). The same cut-point had the smallest area under the ROC curve for LDL particle size. Analyzed separately, the greatest area under the ROC curve for small LDL concentration for whites remained a cut-point of 3.0 (), whereas for blacks it was a TG/HDL ratio cut-point of 2.5 (). For males a TG/HDL ratio cut-point of 2.5 and for females a cut-point of 3.0 was the best marker for small LDL concentration (data not shown).
Figure 1 ROC curves for total, total small, medium small, and very small LDL particle concentrations and LDL particle size A, at a TG/HDL ratio and B, cut-point of 3 in all overweight and white overweight youth, and C, cut-point of 2.5 in black overweight youth. (more ...)
For the group as a whole, the area under the ROC curve showed little difference between the 2 cut-points of 120 mg/dL and 145 mg/dL for medium small (area under ROC curve: 0.795 vs 0.787, respectively) or very small (area under ROC curve: 0.810 vs 0.814, respectively) LDL particles. Analyzed by race, a cut-point of 120 mg/dL had the largest area under the curve for white youth, but for blacks, 145 mg/dL was larger (). Analyzed by sex, cut-point of 120 mg/dL had a greater area under the curve for females for medium small (0.828) and very small LDL (0.837). For males, a cut-point of 145 mg/dL was the best marker for medium small (0.797) and very small LDL (0.828).
ROC curves for total, total small, medium small, and very small LDL particle concentrations, and LDL particle size, at a non-HDL cholesterol cut-point of A, 120 mg/dL for overweight white youth and B, 145 mg/dL for overweight black youth.
The presents the characteristics of all participants grouped according to TG/HDL ratio of <3 vs ≥3 and race. Significantly higher BMI, BMI percentile, waist circumference, fat mass, and absolute and percentage visceral and subcutaneous abdominal fat mass were observed in participants with a TG/HDL ratio of ≥3 compared with those with a ratio of <3. Youth with a TG/HDL ratio of ≥3 had higher concentrations of total cholesterol, TG, non-HDL cholesterol, and very low-density lipoprotein TG and lower concentrations of HDL cholesterol than those whose TG/HDL ratio was <3. There was a significant race difference between the 2 groups, with more black children with a TG/HDL ratio of <3 than ≥3. There was a significant main effect of race for visceral adiposity, total cholesterol, TG, LDL cholesterol, and non-HDL cholesterol. Black youth grouped according to a TG/HDL ratio of <2.5 vs ≥2.5 had lower visceral fat (43.3 ± 3.2 cm2
vs 69.1 ± 10.4 cm2
=.027). There were no TG/HDL ratio by race interactions for any variables presented in the .
Participant characteristics by TG/HDL ratio and race
presents the LDL subclass concentrations and particle size by TG/HDL ratio of <3 vs ≥3 and by race. Children with a TG/HDL ratio of ≥3 had significantly higher concentrations of total LDL, medium small, and very small LDL, and IDL particles (72.2 ± 8.3 vs 28.9 ± 3.1 nmol/L, P < .001) and lower concentrations of large LDL particles with smaller LDL particle size than youth with a TG/HDL ratio of <3 (). There was a tendency for total LDL to be higher in white children (P =.072). No significant interactions were found for LDL particles grouped by TG/HDL ratio and race; however, total LDL, IDL (interaction P =.060), and medium small LDL tended to be greater in white than in black children with a TG/HDL ratio of ≥3.
Concentrations of A, total, B, large, C, medium small, and D, very small LDL, and E, LDL particle size in black and white youth with a TG/HDL ratio <3 and ≥3. Differences compared using 2-way ANOVA. NS, not significant.
Total small LDL concentrations were significantly correlated with BMI (r = 0.337, P < .0001), BMI percentile (r = 0.386, P < .0001), percentage body fat (r = 0.328, P < .0001), fat mass (r = 0.405, P < .0001), waist circumference (r = 0.436, P < .0001), visceral fat (r = 0.529, P < .0001), and TG/HDL ratio (r = 0.668, P < .0001) but not age or Tanner stage. Similar correlations were seen for medium and very small LDL particles, while for LDL particle size, significant negative correlations were observed.
In multiple regression analysis with total small LDL as the dependent variable and age, sex, race, Tanner stage, BMI, and TG/HDL ratio as the independent variables, TG/HDL ratio (partial r = 0.658, P < .001) and BMI (partial r = 0.305, P < .001) explained 71% of the variance in total small LDL concentration. These contributions remained similar when BMI was substituted by BMI percentile, percentage body fat, or fat mass. When BMI was substituted by waist circumference, together with TG/HDL ratio they explained 79% of the variance in small LDL (TG/HDL ratio partial r = 0.733, P < .001; waist circumference partial r = 0.359, P < .001). When visceral fat replaced waist circumference, 74% of the variance in small LDL was explained by TG/HDL ratio (partial r = 0.603, P < .001) and visceral fat (partial r = 0.433, P < .001). In multiple regression analyses with LDL particle size as the dependent variable, BMI (partial r = −0.320, P < .001) and TG/HDL ratio (partial r = −0.621, P < .001), or waist circumference (partial r = −0.335, P =.001) and TG/HDL ratio (partial r = −0.594, P < .001), both explained ~68% of the variance in LDL particle size.