The difference between the glucose concentrations in plasma and whole blood

The glucose concentrations in whole blood (WB) and plasma (P), both prediluted with distilled water and saline, and in their protein-free filtrates, were determined with the Hoffman ferricyanide method. In whole blood prediluted with distilled water the glucose concentration appeared to be 13% higher than in whole blood prediluted with saline. In plasma, predilution with distilled water or saline did not result in different glucose values. Plasma glucose is significantly higher than whole blood glucose independent of the method of pretreatment. A direct relationship between the two values exists, which for protein-free filtrates is represented by Glu(P) equals 1.07 Glu(WB) + 0.11. The glucose concentrations in erythrocytes were calculated and also correlated to plasma glucose values. A good correlation was found when protein-free filtrates were used. Apparently, conversion factors from whole blood to plasma glucose may be used only in cases where samples are deproteinized.