hypoglycemia
Measuring Hypoglycemia
Blood glucose levels discussed in this article are venous plasma or serum levels measured by standard, automated glucose oxidase methods used in medical laboratories and offered through diabetic supply firms. For clinical purposes, plasma and serum levels are similar enough to be interchangeable. Arterial plasma or serum levels are slightly higher than venous levels, and capillary levels are typically in between. This difference between arterial and venous levels is small in the fasting state but is amplified and can be greater than 10% in the postprandial state. On the other hand, whole blood glucose levels (e.g., by fingerprick meters) are about 10%-15% lower than venous plasma levels. Furthermore, available fingerstick glucose meters are only warranted to be accurate to within 15% of a simultaneous laboratory value under optimal conditions, and home use in the investigation of hypoglycemia is fraught with misleading low numbers. In other words, a meter glucose reading of 39 mg/dL could be properly obtained from a person whose laboratory serum glucose was 53 mg/dL; even wider variations can occur with "real world" home use. Ironically, most meters sold are routinely tested for accuracy at the high-end of the scale, sometimes up to 800 mg/dL, despite the fact that there is little immediate danger from hyperglycemia, whereas there is very real immediate danger from hypoglycemia, making accuracy at the low-end extremely critical.
Two other factors significantly affect glucose measurement: hematocrit and delay after phlebotomy. The disparity between venous and whole blood concentrations is greater when the hematocrit is high, as in newborn infants, or adults with polycythemia. High neonatal hematocrits are particularly likely to confound glucose measurement by meter. Second, unless the specimen is drawn into a fluoride tube or processed immediately to separate the serum or plasma from the cells, the measurable glucose will be gradually lowered by in vitro metabolism of the glucose at a rate of approximately 7 mg/dL/hr, or even more in the presence of leukocytosis.
Thank you for viewing our original diabetes instructional video. We urge all diabetics to request a free diabetic alliance diabetes guide, and many will qualify for a free glucose meter as well.