We read with interest the data on the long-term risks of untreated mild hyperglycemia from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study. Any national or international debate on the diagnostic criteria for gestational diabetes mellitus (GDM) also should be informed by the changes in preanalytical laboratory standards for measuring maternal plasma glucose since HAPO. 

For the HAPO study, glycolysis was inhibited by placing samples in a sodium fluoride additive on an ice water slurry and cell separation within 60 minutes.2 Since 2011, it is recommended that cell separation takes place within 30 minutes and if this is not possible that sample tubes contain citrate buffer, not sodium fluoride.3 

In 121 women selectively screened for GDM with a 1-step 75-g oral glucose tolerance test in our hospital, the stricter guidelines increased the rate of GDM from 14.2% (n = 22) under customary conditions to 38.1% (n = 59) applying the 2011 standards (P < .01).4 Failure to implement contemporary laboratory standards may lead to the diagnosis of GDM being missed and to underestimation of the prevalence.