May 06, 2019
2 min read

Test can pinpoint children who do not fast before lab work

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Photo of Jack Yanovski
Jack A. Yanovski

A study conducted by researchers at the NIH suggested that children who did not fast before blood work had significantly lower serum free fatty acids, or FFAs. A biochemical test that could demonstrate which patients are adhering to fasting rules for blood work by measuring FFA levels would be a valuable clinical tool, they said.

“Inadequate fasting can increase glucose concentrations and lead to incorrect diagnoses and therefore more unnecessary laboratory testing,” Jack A. Yanovski, MD, PhD, chief of the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, told Infectious Diseases in Children.

Although data from children are lacking, a survey of adults at the time of morning blood draws showed that only 60% had properly fasted for 12 hours, the researchers noted. Yanovski and colleagues wrote that no currently accepted method, other than the patient report, is available to identify patients who have not fasted.

The researchers explained that FFA concentrations rise in the fasted state but decrease with food intake — regardless of obesity status. They conducted an analysis of children aged 5 to 18 years to determine if testing FAA concentrations would be superior to glucose or insulin concentrations to distinguish between fed and fasting state children. The analysis included children with healthy weight, overweight and obesity.

According to the researchers, the area under the curve of FFA was significantly better than glucose or insulin for identifying children who did not fast (P < .001). An FFA level of less than 287 mEq/mL had a sensitivity of 99% and a specificity of 98% for nonfasting.

The researchers noted that the mean FFA was lower among children in outpatient care compared with those in inpatient care (P < .001). However, children were more likely to be labeled as nonfasting in outpatient care (9.7%) compared with inpatient care (1.6%; P < .001).

Yanovski said a test for FAA concentrations is readily available at clinical laboratories, where they can be obtained with glucose measurements.

“A low FFA value would be helpful if other lab tests, like glucose or triglycerides, are abnormally high,” he said. “The lower the FFA, the more likely the child is to have consumed calorie-containing items that morning. Before ordering additional testing, health care providers can determine if the FFA is consistent with nonfasting. If the FFA value is low, providers can ask parents and the child how successful the child was at fasting for the test. If the child was not fasting, this knowledge could help avoid the need for additional unnecessary testing.”– by Katherine Bortz

Disclosures: The authors report no relevant financial disclosures.