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"If you look at the currently used thresholds to identify young people with high-risk cholesterol and blood fat levels, they use the same threshold across all ages" senior investigator Ian Janssen, MD, from the Queen's University, Kingston, Ontario, stated. "The problem with that is that you are going to see changes, usually increases, in cholesterol levels across the age range, which reflect, to a large degree, natural changes that occur as people get older...What we did was rather than lumping everybody in together, we developed age-specific and gender-specific cut-off points that should help provide a more accurate diagnosis of these high-risk levels."
The purpose of the study, explained Dr. Janssen, was to establish new criteria that would help clinicians identify adolescents with elevated low-density lipoprotein (LDL) and total cholesterol levels, as well as elevated triglyceride levels and low high-density lipoprotein (HDL) cholesterol levels. He noted that the existing cutoff points for identifying borderline-abnormal and abnormal lipoprotein concentrations are represented by the 75th and 95th percentiles (25th and 5th for HDL cholesterol) of the population distribution. As these apply to all youth aged 2 to 19 years, these percentiles have a limited ability to predict adolescents who will have high-risk lipoprotein levels as adults, Dr. Janssen said.
To create the new classification system, the researchers used total cholesterol, LDL cholesterol, HDL cholesterol, and triglyceride measurements of more than 6000 people aged 12 to 20 years, all of whom participated in the National Health and Nutritional Examination Surveys (NHANES) conducted between 1988 and 2002. Investigators developed age- and gender-specific growth curves, similar to what is currently used to monitor height, weight, and body mass index in children and adolescents. The curves were then linked to the adult National Cholesterol Education Program (NCEP) Adult Treatment Panel III to allow clinicians, by extrapolating from the adolescent lipid levels, to determine future cardiovascular risks as an adult.
Table 1. Age-specific Cutoff Points for Females (mmol/L)*
|
Age, y |
Borderline-High
Total Cholesterol |
High Total
Cholesterol |
Borderline-High
LDL Cholesterol |
High LDL
Cholesterol |
|
12 |
4.77 |
5.47 |
2.96 |
3.52 |
|
13 |
4.71 |
5.41 |
2.98 |
3.55 |
|
14 |
4.68 |
5.38 |
3.00 |
3.57 |
|
15 |
4.72 |
5.46 |
3.03 |
3.61 |
|
16 |
4.82 |
5.62 |
3.07 |
3.68 |
|
17 |
4.94 |
5.82 |
3.13 |
3.77 |
|
18 |
5.07 |
6.03 |
3.22 |
3.90 |
|
19 |
5.16 |
6.17 |
3.32 |
4.06 |
|
20 |
5.18 |
6.22 |
3.37 |
4.14 |
|
Age, y |
Low HDL
Cholesterol |
Protective HDL
Cholesterol |
Borderline-High
Triglycerides |
High Triglycerides |
|
12 |
1.03 |
1.48 |
1.60 |
2.03 |
|
13 |
1.04 |
1.47 |
1.53 |
1.93 |
|
14 |
1.04 |
1.48 |
1.47 |
1.82 |
|
15 |
1.03 |
1.49 |
1.44 |
1.79 |
|
16 |
1.03 |
1.51 |
1.46 |
1.83 |
|
17 |
1.03 |
1.53 |
1.53 |
1.94 |
|
18 |
1.03 |
1.54 |
1.61 |
2.09 |
|
19 |
1.03 |
1.55 |
1.68 |
2.22 |
|
20 |
1.04 |
1.55 |
1.70 |
2.26 |
|
*To convert total cholesterol, LDL cholesterol, and HDL cholesterol levels to mg/dL, multiply by 38.67. To convert triglyceride levels to mg/dL, multiply by 88.5. Source: Circulation. Posted online August 28, 2006.
|
Table 2. Age-specific Cutoff Points for Males (mmol/L)*
|
Age, y |
Borderline-High
Total Cholesterol |
High Total
Cholesterol |
Borderline-High
LDL Cholesterol |
High LDL
Cholesterol |
|
12 |
5.18 |
6.03 |
3.24 |
3.98 |
|
13 |
4.99 |
5.83 |
3.15 |
3.86 |
|
14 |
4.86 |
5.70 |
3.08 |
3.76 |
|
15 |
4.84 |
5.70 |
3.06 |
3.74 |
|
16 |
4.88 |
5.77 |
3.11 |
3.81 |
|
17 |
4.95 |
5.88 |
3.18 |
3.91 |
|
18 |
5.05 |
6.02 |
3.25 |
4.00 |
|
19 |
5.14 |
6.16 |
3.32 |
4.09 |
|
20 |
5.18 |
6.22 |
3.37 |
4.14 |
|
Age, y |
Low HDL
Cholesterol |
Protective HDL
Cholesterol |
Borderline-High
Triglycerides |
High Triglycerides |
|
12 |
1.13 |
1.70 |
1.44 |
1.84 |
|
13 |
1.10 |
1.64 |
1.48 |
1.93 |
|
14 |
1.07 |
1.59 |
1.52 |
2.02 |
|
15 |
1.04 |
1.55 |
1.56 |
2.10 |
|
16 |
1.03 |
1.53 |
1.59 |
2.16 |
|
17 |
1.03 |
1.53 |
1.62 |
2.20 |
|
18 |
1.03 |
1.54 |
1.65 |
2.24 |
|
19 |
1.04 |
1.55 |
1.68 |
2.26 |
|
20 |
1.04 |
1.55 |
1.70 |
2.26 |
|
*To convert total cholesterol, LDL cholesterol, and HDL cholesterol levels to mg/dL, multiply by 38.67. To convert triglyceride levels to mg/dL, multiply by 88.5. Source: Circulation. Posted online August 28, 2006. |
Dr. Janssen noted that the cutoff points changed over time. For example, LDL cholesterol levels denoting high risk changed from 3.52 mmol/L in 12-year-old girls to 4.14 mmol/L at age 20 years. One advantage of the age- and sex-specific threshold is that adolescents will not be misdiagnosed simply because they are on a different part of the growth curve, say investigators.
"We need to consider measuring cholesterol values in young people, which pediatricians know already," said Dr. Janssen. "But we need to start taking into consideration the person's age when we're trying to define whether or not they're at risk." | 
