Fasting before blood tests may not be necessary for children
With the unprecedented expansion of overweight, obesity and pre-diabetes in the pediatric population it is becoming increasing important to evaluate metabolic status with appropriate blood tests at a younger age. Anything that makes this task less onerous is desirable. A welcome study just published in the journal Pediatrics offers evidence that fasting may not be necessary to reliably evaluate lipid status in children. The authors state:
"Fasting lipid panels are recommended to screen for lipid abnormalities; however, fasting can be difficult for children and make screening difficult. Results of studies in adult patients are raising questions of whether fasting is needed before lipid screening."
They examined total cholesterol (TC), HDL (high-density lipoprotein), LDL (low-density lipoprotein), and triglyceride cholesterol components in relation to fasting in 12,744 children aged 3 to 17 (varying times for young children and the usual fasting for those older than 12 years). The data appear to give kids a break:
"TC, HDL, LDL, or triglyceride values were available for 12 744 children. Forty-eight percent of the TC and HDL samples and 80% of the LDL and triglyceride samples were collected from children who had fasted ≥8 hours. Fasting had a small positive effect for TC, HDL, and LDL, resulting in a mean value for the sample that was 2 to 5 mg/dL higher with a 12-hour fast compared with a no-fast sample. Fasting time had a negative effect on triglycerides, which resulted in values in the fasting group that were 7 mg/dL lower."
Furthermore...
"For TC, nonfasting screening inappropriately classifies ≈1% of children as normal, who would have had borderline values with fasting. In addition, ≈1% of children with borderline nonfasting values would actually have elevated results if fasting. For LDL, 1.2% of children with borderline fasting levels would have normal results postprandially, and 1.6% of children with increased calculated LDL while fasting, would now be considered to have borderline results. For triglycerides,≈4% of the children classified with normal triglycerides when fasting would have elevated values postprandially."
In other words, most of the time the difference between fasting and non-fasting in children is not clinically significant.The authors conclude:
"Comparing a nationally representative cross-section of children who had fasted for various lengths of time, we demonstrated that nonfasting measurements of TC, calculated LDL, and HDL cholesterol values had only small differences from fasting values. Although statistically significant, these differences are unlikely to result in important clinical changes in the results of screening for cholesterol abnormalities. ...Across a large, nationally representative sample of children, the levels of TC, HDL, non-HDL cholesterol, and LDL cholesterol vary minimally on the basis of fasting time. It is not known if these small differences in lipoprotein components consistently weaken or strengthen the usefulness of lipid values for the assessment of current health risks or prediction of future cardiovascular risks, but it is clear that testing regardless of fasting status would reduce barriers to screening. Therefore, future research with people in longitudinal samples is warranted. If those results confirm our findings, professional societies might wish to reconsider their recommendations and encourage providers follow lipid screening guidelines at the point of care, regardless of fasting status."
It will be helpful if future studies can offer data specifically quantifying the impact of fasting versus non-fasting on subsequent cardiovascular and metabolic risks. However, on the basis of the evidence we have now, my personal preference is to make it as easy on the kids as possible. Fasting a galloping pediatric metabolism risks a low blood sugar state that is not only globally miserable but elicits a vasoconstrictive autonomic response that makes phlebotomy much more difficult and traumatic.