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Biomarker identifies children who eat before blood tests

Children sometimes eat before coming in for blood tests, despite instructions to the contrary. Jecapix / E+ / Getty Images

More than 18% of children in the United States are considered obese. Children with obesity face many of the same health risks as adults with obesity, including high blood pressure and type 2 diabetes. Guidelines recommend that doctors screen children with obesity for type 2 diabetes so the condition can be caught and treated early.

A common blood test for diabetes requires that people fast overnight beforehand. Eating before such a test can cause blood sugar (glucose) levels to rise. Increased blood glucose levels can falsely suggest diabetes, leading to follow-up testing and uncertainty.

Children who come in for blood tests for diabetes may sometimes eat before the test, despite instructions to the contrary. No laboratory method currently exists to tell whether or not a child has eaten before a blood test.

Researchers led by Dr. Jack Yanovski from NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) examined whether measuring substances in the blood called free fatty acids (FFAs) could detect whether a child had eaten before a blood test. FFAs are produced when the body burns fat. After a meal, blood glucose levels go up and FFAs are stored in fat cells, so FFA levels should be lower if a child has eaten than if they’d fasted all night.

The team used blood samples from more than 1,000 children at the NIH Clinical Center. About a third of the children had samples taken after fasting while they were staying in the hospital (inpatients). Another third had samples taken both during fasting and then 2 hours after being given glucose. A final third had been instructed to fast the night before and came in the morning for testing as outpatients.

The researchers measured blood glucose, insulin, and free fatty acid levels in all samples. They then looked for a cut-off point for FFAs that could potentially distinguish samples taken while fasting from samples taken after eating. The study was funded by NICHD and others. Results were published on May 3, 2019, in Pediatrics.

As expected, blood glucose levels in samples rose after the children drank the sugar, while FFA levels fell. Blood FFA levels could identify 99% of the blood samples taken after glucose intake. FFA levels could also identify 98% of samples taken when the children were fasting. This was true whether the children were overweight, obese, or normal weight.

The researchers determined a cut-off point for FFAs that could separate blood samples taken after fasting from those taken after eating. By this measurement, 9.7% of children who came in as outpatients to have blood drawn had eaten in the morning despite instructions not to. In contrast, less than 1.6% of the inpatients had samples suggesting they ate before their test.

“A test that could lower the number of false positives for diabetes could reduce the need for re-testing, spare families unnecessary worry, and lower the costs of screening for diabetes in children,” Yanovski says.