Blood Collection Tubes Utilized for Fasting Blood Sugar Measurement

A Source of Variation in Clinical Laboratory Test Results

Abstract

Background. Diabetes mellitus (DM) remains a major global health burden, with increasing prevalence in developing countries such as the Philippines. Accuracy of glucose measurement is vital for diagnosis and management; however, preanalytical variables, particularly glycolysis from varying collection tubes, temperature and time interval can significantly affect test results. Despite guideline recommendations favoring plasma, serum is still commonly used in local clinical practice.

Objective. This study evaluated the effectiveness of different commercially available blood collection tubes in preserving glucose stability by minimizing pre-analytical glycolysis.

Methodology. A cross-sectional observational and quasi-experimental study was conducted among 40 healthy adult participants (18–59 years) from a tertiary institution in Quezon City, Philippines. A total of 160 samples were collected using four tube types (one plasma and three serum tubes). Samples were analyzed at varying time intervals (0–180 minutes) and storage conditions (room temperature and 4°C). Glucose levels were measured using the glucose oxidase method. Statistical analysis included Shapiro–Wilk, Kruskal–Wallis H-test, Welch’s t-test, and Dwass–Steel–Critchlow–Fligner post hoc comparisons at a 1% significance level.

Results. Glucose concentrations differed significantly across tube types (p <0.001) and time intervals (p <0.001), but not by storage temperature (p = 0.023). Plasma samples demonstrated significantly higher glucose levels than serum samples, with all serum tubes showing a consistent negative bias relative to the fluoride-containing plasma tube. Although differences remained within the  ± 6 mg/dL CLIA allowable total error, clinically relevant deviations were observed near diagnostic thresholds. Glucose stability significantly declined beyond 60 minutes, indicating ongoing glycolysis despite sample separation.

 Conclusion. Blood collection tube type and delayed processing significantly influence glucose measurements. While acceptable within analytical limits, systematic biases may affect clinical interpretation. Standardization of blood collection practices and stricter pre-analytical protocols are essential to improve diagnostic accuracy for diabetes in the Philippines.