symptoms of canine diabetes

Glycated hemoglobin is abnormally high in diabetics with chronic hyperglycemia and reflects their metabolic control. It is produced by nonenzymatic condensation of glucose molecules with free amino groups on the globin component of hemoglobin. The higher the prevailing ambient levels of blood glucose, the higher will be the level of glycated hemoglobin.
The major form of glycohemoglobin is termed hemoglobin A1c, which normally comprises only 4-6% of the total hemoglobin. The remaining glycohemoglobins (2-4% of the total) consist of phosphorylated glucose or fructose and are termed hemoglobin A1a and hemoglobin A1b. Some laboratories measure the sum of these three glycohemoglobins and report it as hemoglobin A1, but more laboratories are converting to the more intricate but highly specific HbA1c assay. There are now monoclonal immunoassays for measuring HbA1c. Machines based on this technology can be used in clinicians' offices. They use capillary blood and give a result in about 9 minutes, allowing immediate feedback to the patients regarding their glycemic control.
Since glycohemoglobins circulate within red blood cells whose life span lasts up to 120 days, they generally reflect the state of glycemia over the preceding 8-12 weeks, thereby providing an improved method of assessing diabetic control. Measurements should be made in patients with either type of diabetes mellitus at 3- to 4-month intervals so that adjustments in therapy can be made if glycohemoglobin is either subnormal or if it is more than 2% above the upper limits of normal for a particular laboratory. In patients monitoring their own blood glucose levels, glycohemoglobin values provide a valuable check on the accuracy of monitoring. In patients who do not monitor their own blood glucose levels, glycohemoglobin values are essential for adjusting therapy. Use of glycohemoglobin for screening is controversial. Sensitivity in detecting known diabetes cases by hemoglobin A1c measurements is only 85%, indicating that diabetes cannot be excluded by a normal value. On the other hand, elevated hemoglobin A1c assays are fairly specific (91%) in identifying the presence of diabetes.
Occasionally, fluctuations in hemoglobin A1 are due to an acutely generated, reversible, intermediary (aldimine-linked) product that can falsely elevate glycohemoglobins when measured with "short-cut" chromatographic methods. This can be eliminated by using specific HPLC methods that detect HbA1c or by dialysis of the hemolysate before chromatography. When hemoglobin variants are present, such as negatively charged hemoglobin F, acetylated hemoglobin from high-dose aspirin therapy, or carbamoylated hemoglobin produced by the complexing of urea with hemoglobin in uremia, falsely high "hemoglobin A1" values are obtained with commonly used chromatographic methods. In the presence of positively charged hemoglobin variants such as hemoglobin S or C, or when the life span of red blood cells is reduced by increased hemolysis or hemorrhage, falsely low values for "hemoglobin A1" result.
(current MD&T 2005)