How is lipid testing performed in children?

Updated: Jun 27, 2019
  • Author: Henry J Rohrs, III, MD; Chief Editor: Stuart Berger, MD  more...
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Lipids can be routinely measured individually as total cholesterol (TC), triglycerides (TGs), or high-density lipoprotein cholesterol (HDL-C). Using these measurements and the Friedewald equation when TG levels are less than 400 mg/dL, low-density lipoprotein cholesterol (LDL-C) can be calculated. Direct LDL measurements allow LDL-C determination on specimens when the TG level is 400 mg/dL or higher and do not require a fasting specimen. However, direct LDL-C measurements have no advantage (and add needless expense) when the TGs levels are below 400 mg/dL.

Children should be on their regular diet for 4-6 weeks before lipid testing. Recent changes in diet that may change lipid levels are an indication to delay testing. Measurements of TC and HDL-C do not need to be performed in the fasting state. However, isolated TG measurements and lipid profile measurements should follow an overnight fast of least 8 hours, preferably 12-14 hours.

Recent severe illness (eg, hospitalization within the last 4-6 wk) is a contraindication to lipid testing because significant stress can also lead to transient decreases in lipid levels or transient lipid abnormalities (eg, hypertriglyceridemia following diabetic ketoacidosis). During acute illness, lipids should not be measured unless hypertriglyceridemia is believed to be the underlying cause of the disease (eg, pancreatitis). Lipoproteins are negative acute phase reactants and their concentrations decline within 24 hours of severe acute stress. In adults, intraindividual variation in TC over the course of one year is reported to be ±8% (range 4%-11%). Intraindividual variation in TG is 13%-41%, whereas HDL-C varies by 4%-12%. Standing TC levels are 8%-12% higher than recumbent values because of a decrease in intravascular fluid that leaks into the interstitial space. The use of anticoagulants in sample tubes may lower TC levels by 3% or less.

Historically, an overnight fast was deemed necessary before lipid screening, but adult data suggest nonfasting lipids may be appropriate for initial screening for cardiovascular risk. [6, 7, 8, 9, 10] A large, cross sectional study was performed in children to assess differences in lipid values based on fasting status. [11] Mora found that although statistically significant differences existed in nonfasting lipid levels, these differences were not clinically significant, with more than 95 percent of children falling into the same classification category whether lipids were fasting or nonfasting.

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