Whole Blood Glucose: What are We Actually Measuring?

Removal of erythrocytes from blood specimens before performing clinical chemistry tests on plasma or serum has been a basic procedure for many years. Particulate matter causes problems in analytical methods and red blood cells occupy a significant volume. Lysis of the cells releases substances in different concentrations from those in plasma and some cell constituents interfere in assay techniques, e.g. haemoglobin in colorimetric methods. For most assays, therefore, the homogeneous medium of plasma or serum has been considered to be preferable. One of the few exceptions to this has been glucose assay, in which either whole blood or plasma has been used. The advantages of whole blood are in the time saved in not having to separate blood components and in not requiring the availability of a centrifuge. In a laboratory environment, this may not matter too much, but in a clinic or site of near-patient testing, it assumes greater importance. For this reason, virtually all of the near-patient systems for glucose employ whole blood, applied directly from a finger-prick, as the sample.