Laboratory and home based monıtorıng of blood glucose

Blood glucose testing

Venous plasma or serum has the advantage over whole blood of providing values for glucose that are independent of hematocrit and reflect levels in the interstitial spaces.  For these reasons and because plasma and serum lend themselves to automated analytic procedures ­they are used in most laboratories. The glucose con­centration is 10-15 % higher in plasma or serum than in whole blood because structural components of blood cells are absent. Whole blood glucose determi­nations are seldom used in clinical laboratories but have been used by diabetic patients during self-moni­toring of capillary blood glucose, a technique widely accepted and recommended now the management of diabetes mellitus. Recently, however, many new reflectance meters have been     modified to directly record serum glucose rather than to calculate whole blood glucose concentrations.

Venous blood samples

The laboratory methods regularly used for deter­mining plasma glucose utilize enzymatic methods (such as
glucose oxidase or hexokinase), colorimetric methods (such as a toluidine), or automated methods. The automated methods utilize reduction of copper or iron compounds by reducing sugars in dialyzed serum. They are convenient but are not specific for glucose, since they react with other reducing sub­stances (which are elevated in azotemia or with high ascorbic acid intake). Samples should be collected in tubes containing sodium fluoride, which prevents glycolysis in the blood sample that would artifactually lower the mea­sured glucose level. If such tubes are not available, samples must be centrifuged within 30 minutes of collection and the plasma or serum stored at 4 °C.



Capillary blood samples

Several strip (glucose oxidase) based methods for use with portable, battery operated reflectance meters that give a digital readout are now available. First-generation reflectance meters required exact timing by the operator as well as careful removal of all traces of blood from the strip prior to reading of the colour. Second-generation devices have eliminated these two potential sources of technical error by providing automatic timing and allowing quantitation without removal of the blood. The tim­ing required for glucose measurements by these meters varies from 12 sec­onds to 45 seconds and as little as 2-5 mL of blood are needed for analysis by most meters. To monitor their own blood glu­cose levels, patients must prick their fingers with a 21-gauge lancet, a procedure that can be facilitated by a small plastic trigger device. Third-generation devices are presently in the de­velopmental stage and represent a noninvasive method relying on infrared absorption spectra, which allow quantitation of glycemia flowing through capil­lary beds of the finger or earlobe. Present pilot mod­els are relatively large and expensive, but they appear to be accurate and have the great advantage of elimi­nating painful pricks to the fingers (8,9).

Testing for Ketonuria / Ketonemia

Commercial products are available to test for the presence of ketones in the urine. Most strips utilize a nitroprusside re­action that measures only acetone and acetoacetate. Although these tests do not detect b-hydroxybutyric acid, which lacks a ketone group, the semi quantitative estimation of the other ketone bodies is nonethe­less usually adequate for clinical assessment of ketonuria. Other conditions besides diabetic ketoacidosis may cause ketone bodies to appear in the urine; these in­clude starvation, high-fat diets, alcoholic ketoacido­sis, fever, and other conditions in which metabolic re­quirements are increased. Serum ketone measurements, using strip-based technology has also now become available.

Glycosylated hemoglobin

Glycohemoglobin (GHb) is produced by a ke­to-amine reaction between glucose and the amino ter­minal amino acid of both beta chains of the hemoglo­bin molecule. The major form of glycohemoglobin (Hb A1C), which normally comprises only 4-6% of total hemoglobin, is abnormally elevated in diabetics. The glycosylation of hemoglobin is dependent on the concentration of blood glucose. The reaction is not reversible, so that the half-life of glycosylated he­moglobin relates to the life span of red cells (which normally circulate for up to 120 days). Glyco­hemoglobin generally reflects the state of glycemia over the preceding 8-12 weeks, thereby providing a method of assessing chronic diabetic control (10).