Problems with the use of whole blood as a sample material in novel direct glucose analysers.

We report a marked shift in whole-blood glucose measurements when a widely available glucose analyser is used. We compared a conventional glucose dehydrogenase (GDHG) method after protein precipitation and a direct polarographic method in conjunction with immobilized glucose oxidase. The polarographic method gave mean whole blood glucose levels from 79% to 95% of those measured by the GDHG method. No such difference was found in either plasma or serum samples or in water-based control samples. The stability of glucose in fluoride oxalate tubes appears to be poorer than is usually assumed. We observed a 5-10% decrease in whole-blood glucose concentrations during the first hour after sampling under routine conditions.