Excess weight alters results of blood tests in kids and teens

Outcomes of nearly 70 percent of common lab tests vary with weight, a new study found

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In a new study, weight affected the results of nearly 7 in 10 routine blood tests in kids.

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Even in children and teens, obesity has been linked to major health problems, such as diabetes and heart disease. But the effects of extra weight may show up in some tests before disease develops. Weight can affect results of routine blood tests in kids, new data show. And those results might highlight kids at risk of developing disease. 

Victoria Higgins is a research scientist at The Hospital for Sick Children in Toronto, Canada. She is part of a large team working to identify normal ranges for the values measured by blood tests. These ranges can vary with age, sex and ethnicity. But Higgins realized no one had looked to see if weight, too, might have an effect.

She and her colleagues analyzed blood samples from more than 1,300 healthy children and teens in Toronto. The researchers performed 35 common tests using the blood. Then they grouped the samples by different measures of the kids’ weight status. These included things such as waist size and body mass index, or BMI. This allowed the researchers to compare the results from kids in healthy weight, overweight and obese BMI ranges. 

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Blood tests from kids who carried some extra pounds showed differences in liver function, cholesterol levels and signs of inflammation. Such changes could signal risk of developing disease.SerhiiBobyk/iStock/Getty Images Plus

Results of 24 of the 35 blood tests were affected by weight, they found. That’s almost seven in every 10. Among those affected were tests of liver function, lipids (fatty substances, such as cholesterol) and signs of inflammation. 

Sometimes, levels of a substance were higher in heavier people. This was the case for triglycerides (Try-GLIH-sur-ides). This is a type of fat in the blood. Its levels were more than one-third higher in subjects with obesity than in those with healthy weight. Other measures, such as iron levels, fell with increasing weight. Iron tended to be 17 percent lower in kids with obesity compared with those with healthy weight. And someone didn’t need to be obese to be impacted. Outcome differences were largest between kids with obese and healthy weight BMIs. But results of some blood tests were affected by smaller weight differences too, not just obesity. Higgins and her team shared their findings December 17 in the Journal of Clinical Endocrinology & Metabolism.

What’s behind the differences?

Two things might explain the findings, Higgins says. “Normal” blood values for kids with excess weight may simply be different from those with healthy weight. Or, more worrisome, the differences in heavier kids might be an early sign of health problems to come.

“I think this could indicate that even at a very early age, [heavier] kids’ health may be declining in several ways,” Higgins says. 

Reza Hakkak is a nutritionist at the University of Arkansas for Medical Sciences in Little Rock. He was not a part of this study. He does, however, investigate how diet and obesity might affect health problems, such as cancer. 

“Without any intervention, the majority of children with obesity become overweight or obese adults,” he says. If adults don’t step in and help overweight kids, he argues, “they can grow up and have serious health issues in early adulthood.”

This study doesn’t address whether different blood test results seen in heavier kids reflect early disease. All the kids and teens in the study were healthy. Still, Higgins notes, doctors and patients should be aware of the effect of weight on blood tests. It’s possible that kids of different weights need different standards for what is “normal.” But both Higgins and Hakkak believe this is unlikely.

“It could be eye-opening for kids who might think they don’t have to worry about health and diet and exercise until they’re older,” says Higgins. “I think these findings show that it’s always important to live a healthy lifestyle.”

Hakkak agrees: “Early intervention is key here. It helps kids not develop chronic diseases later on.” Chronic diseases, those that develop slowly and then may last for the rest of your life, include heart disease, diabetes, Alzheimer’s and possibly cancer. For such diseases, he notes, “The name of the game is prevention. And the best treatments are physical activity and a healthy diet.”

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