Have Your Patients Truly Fasted for Their Early Morning Blood Work? Free Fatty Acids
May Tell All
LewisFirst, MD, MS, Editor in Chief, Pediatrics
Ever order fasting morning blood work only to wonder when the results come back if
the patient had actually fasted? Concerned about this problem, Collins et al. (10.1542/peds.2018-3896) decided to see if the concentration of serum free fatty acid (FFA) might be a marker
to indicate a fasting or nonfasting state. The authors compared FFA levels in 442
fasting inpatient children and 323 outpatient children who were to have fasted and
then receive a glucose load as part of an oral glucose tolerance test and found that
FFA levels performed better than glucose or insulin for identifying non-fasting state.
In fact the authors determine that a level of FFA < 287 mEq/ml had 99% sensitivity
and 98.0% specificity for non-fasting. When children were tested for FFA levels in
the inpatient and outpatient setting, the authors found that 9.7% of those in the
outpatient setting compared to 1.6% in the inpatient setting had FFA values suggestive
of non-fasting. What does this mean? It suggests that if in doubt about a patient
fasting, you won’t have to chew the fat with parents figuring out if the patient did
or did not fast, but simply draw a FFA level and if it is less than 287 mEq/ml, you
may want to repeat those tests on another day when your patient actually did fast.
Read this study and decide if you want to use FFA as the serologic polygraph test
for true fasting.