Blood Glucose Determinations Differ in Plasma and Serum

The concentration of glucose in the blood will continue to decrease over time after phlebotomy because of glycolysis, which will occur in erythrocytes, white blood cells (WBCs), and platelets as these cells can continue to metabolize glucose.

Laboratory scientists at the University of Mysore, (Manasagangotri, India) investigated the effect of time and the method of processing of blood on the blood glucose levels. Blood from 30 different patients who came for routine blood glucose determination were used in the study. Whole blood was divided into three portions. One portion was allowed to clot. To the second portion, 2mg/mL sodium fluoride was added, and to the third portion, ethylene diamine tetra acetic acid (EDTA)–disodium salt was added.

Blood sugar was estimated using a blood sugar assay kit (Becton Dickinson, Bangalore, India). Optical Density (OD) of the colored complex was measured at 620 nm in an autoanalyzer. Blood sugar in these samples stored at room temperature was measured again after four hours and eight hours. The serum gave values lower than fluoride plasma by 1.15%. Although this difference was statistically significant, it may not be physiologically relevant. On storing the sample at room temperature for eight hours, the serum glucose value decreased by 8% and even fluoride plasma had 4.3% lower glucose.

The authors concluded that blood glucose should be determined within as short a time as possible after drawing the blood. The blood glucose values ranged from 76 to 410 mg/dL covering a wide range of blood glucose values that would be seen in any sample analysis. Serum may be a better sample for blood glucose determination particularly when there is a time delay in the measurement. If appropriate correction is applied, it may actually be a better sample than plasma. Moreover, many clinical analysis procedures require serum rather than plasma and therefore one single drawing of blood may suffice for even blood glucose estimation. The study was published online on May 14, 2012, in the Journal of Clinical Laboratory Analysis.

Related Links:
University of Mysore
Becton Dickinson