Background: Proper pre-analytical handling of blood samples is essential for reliable glucose measurement and for the accurate diagnosis and monitoring of diabetes mellitus. This study aimed to compare glucose concentrations in serum, lithium heparin (Li-Heparin), sodium fluoride citrate (NaF-Citrate), and sodium fluoride (NaF) plasma. Methods: Blood samples from 45 healthy volunteers were collected in Li-Heparin, NaF-Citrate, and serum tubes. Serum was stored at room temperature (RT) for up to 30 min, Li-Heparin whole blood in an ice-water slurry, and NaF-Citrate and Li-Heparin whole blood at RT for up to 10 min. Glucose was measured using the Cobas 8000 c701 analyzer. Additionally, internal routine laboratory data (n > 85,000) were analysed following the switch from NaF to NaF-Citrate tubes in 2015. Results: NaF-Citrate plasma showed the highest positive deviations, up to 3.11% compared with both reference conditions. Li-Heparin plasma at RT was 1.17 % higher than Li-Heparin plasma on ice. Serum glucose did not differ significantly from Li-Heparin plasma on ice. In routine data, the introduction of NaF-Citrate tubes resulted in an average increase of 10.5% in measured glucose concentrations in 2016. Conclusion: Glucose concentrations measured in NaF-Citrate plasma and Li-Heparin plasma (ice or RT) within 30 min after blood collection are not comparable. According to ADA and WHO diagnostic criteria, switching to NaF-Citrate tubes increased the proportion of patients with impaired fasting glucose by 16.9% and impaired glucose tolerance by 8.8%. NaF-Citrate tubes are recommended when immediate centrifugation and plasma separation cannot be ensured.
Flindt et al. (Fri,) studied this question.