Are You Using the Recommended Test Tubes for Glucose Measurement? New Guidelines for Pre-analytical Handling in Germany

For high-quality glucose measurement results, which are required for diabetes diagnosis, treatment decisions, calibration of CGM systems, and so on, reliable pre-analytical handling of the blood samples is important, as recently highlighted in a US diabetes journal. ¹ The recommendation given is to use plasma as the appropriate specimen; however, in daily practice (also in the United States), glucose measurements are frequently made in serum, ie, the recommended test tubes are not used.

Since May 2023, the usage of test tubes for plasma for glucose measurements is now listed in the guidelines of the “Bundesärztekammer” (Rili-BÄK) (see Table B1-1); in addition, if the glucose measurement is not performed within 15 minutes after blood sampling, plasma has to be separated from the cells within this time period or tubes with adequate glycolysis inhibitors have to be used. ² These changes also include the usage of appropriate test tubes for potassium measurements.

This is the first time that a statement about the pre-analytical handling of given laboratory measurands is listed in these guidelines, which are mandatory for all measurements in medical laboratories in Germany. In the context of near-patient immediate diagnostics, measurement in whole blood samples is now recommended (displaying plasma-equivalent values)—with the restriction that measurement must be performed within 15 minutes.

Such changes aim to minimize influencing variables and interfering factors in the pre-analytic phase. In addition to stricter specification of sample treatment, as described earlier, serum is now explicitly stated to be not suitable for blood glucose measurements. Glucose concentrations in serum decrease by around 7% per hour due to glycolysis.^3,4 Thus, these adaptations are particularly beneficial for blood samples that are collected in outpatient care and are often subject to longer transportation times. When used to diagnose or monitor a person with diabetes, for example, these changes eliminate false low-glucose measurement results due to glycolysis. From the view of a patient, elevated glucose levels are no longer overlooked, and poorly controlled patients will be recognized in future, so that in the end, patient safety is improved.

At the same time, the requirements for analytical quality as assessed with external quality controls were adjusted; ie, the measured variable glucose must now meet stricter requirements for internal and external quality assurance. ² We have estimated the impact of such changes on success rates in external quality control schemes by using data from recent evaluations. ⁵ Participation in external quality schemes is not mandatory for point-of-care devices with unit-use reagents in specialized diabetes practices in Germany; however, it is highly recommended.

It is of interest to note that little is known, at least published, about the usage of test tubes for glucose measurement in clinical practice in different countries. Certainly, the manufacturers of such test tubes will know this in detail; however, apparently, neither diabetes associations nor clinical chemistry associations have paid much attention to this topic.

In clinical practice, the recommended test tubes should be used for glucose measurements to improve patient safety.