Vacutainer plasma collection tube

Blood samples were collected into four collection tubes [two Vacutainer serum collection tubes containing no additives (Becton Dickinson, Franklin Lakes, NJ), one Monoject plasma collection tube containing 0.10 mL of 15% K₃EDTA (Covidien, Mansfield, MA), and one Vacutainer plasma collection tube containing 15 mg of sodium fluoride and 12 mg of potassium oxalate (Becton Dickinson) for glucose determination]. Following collection, all tubes were inverted several times. Plasma tubes were immediately placed on ice, while serum tubes were allowed to clot before being placed on ice. Between 1 and 8 h after collection, all samples were centrifuged at 1,500 × g at 4°C for 30 min. Plasma and serum were transferred into multiple 2-mL microcentrifuge tubes and stored at −20°C until analysis.
Maternal plasma glucose, serum urea N, and serum non-esterified fatty acids (NEFA) were analyzed as described in Niederecker et al. (2018) (link), and plasma triglycerides were analyzed as described in Larson-Peine et al. (2022) (link). For each assay, samples were analyzed in duplicate, and pooled control samples were used. The intraassay and interassay CV were 2.7% and 2.2% for plasma glucose, 3.2% and 3.7% for serum urea N, 3.4% and 5.1% for serum NEFA, and 2.8% and 2.3% for plasma triglycerides, respectively.