Different pre-analytical techniques and the results of 50 g oral glucose challenge tests

We aimed to analyse the pre-analytical process and its effect of 50 g of oral glucose challenge test results for screening gestational diabetes mellitus.

The 50 g oral glucose challenge test was performed to 30 pregnant women, and the blood was collected as two samples for three tubes containing; serum separating jell (SSJ), sodium fluoride-potassium oxalate (NaF - KOx) and sodium citrate-containing tube. The first samples of the three tubes were centrifuged within 30 minutes, and second samples were centrifuged after 60 minutes and were analysed. One sample in SSJ tube and was analysed in the same day according to hospitals routine practice. The results were compared.

Among the 30 samples, the mean decrease in glucose levels was highest in the SSJ tube (0.38 mmol/L), followed by 0.16 mmol/L in Na citrate tube and 0.14 mmol/L in NaF-KOx tube. The hospital routine assessment with SSJ was 6.36 ± 1.90 mmol/L. The <30 and >60 minutes glucose results were 6.80 ± 1.88 mmol/L vs 6.42 ± 1.97 mmol/L for SSJ, 5.95 ± 1.60 mmol/L vs 5.78 ± 1.51 mmol/L for Na Citrate and 6.90 ± 1.86 mmol/L vs 6.75 ± 1.90 mmol/L for NaF-KOx mg/dL groups, respectively, and both the changes within time and the results between the tubes showed a statistically significant difference (P < .001).

In cases with longer assessment time and with different blood sample tubes, the clinician should also keep in mind that, especially with results under but close to the cut-off levels, an underdiagnosed gestational diabetes might be present.