Porth's Essentials of Pathophysiology, 4e

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Endocrine System

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releasing adequate insulin to facilitate storage, their blood glucose levels rise above those observed in normal people and remain elevated for longer periods. Capillary Blood Glucose Monitoring. Technological advances have provided the means for monitoring blood glucose levels by using a drop of capillary blood. This procedure has provided health professionals with a rapid and economical means for monitoring blood glucose and has given people with diabetes a way of maintaining near-normal blood glucose levels through self-monitoring of blood glucose. These methods use a drop of capillary blood obtained by pricking the finger or forearm with a special needle or small lancet. Small trigger devices make use of the lancet virtually painless. The drop of capillary blood is placed on or absorbed by a reagent strip, and glucose levels are determined elec- tronically using a glucose meter. Laboratory tests that use plasma for measurement of blood glucose give results that are 10% to 15% higher than the finger-stick method, which uses whole blood. 28 Many blood glucose monitors approved for home use and some test strips now calibrate blood glucose read- ings to plasma values. It is important that people with diabetes know whether their monitors or glucose strips provide whole-blood or plasma test results. Continuous glucose monitoring (CGM) systems are becoming available to fine-tune glucose management. The various systems have small catheters implanted in the subcutaneous tissue to provide frequent samples. The variety and accuracy of these systems are continu- ally improving. Finger-stick glucose monitoring remains the standard of care, but does not provide as much information regarding the glycemic profile as CGM (especially during the overnight period). Glycosylated Hemoglobin. Glycosylated hemoglobin, hemoglobin A 1C (HbA 1C ), and A1C are terms used to describe hemoglobin into which glucose has been incor- porated. Hemoglobin normally does not contain glu- cose when it is released from the bone marrow. During its 120-day life span in the red blood cell, hemoglobin becomes glycosylated to form HbA1. The major form of HbA1 is HbA 1C , which makes up 2% to 6% of total hemoglobin. 3 Because glucose entry into red blood cells is not insulin dependent, the rate at which glucose becomes attached to the hemoglobin molecule depends on blood glucose levels. Glycosylation is essentially irre- versible, and the level of A1C present in the blood pro- vides an index of blood glucose levels over the previous 6 to 12 weeks. In uncontrolled diabetes or diabetes with hyperglycemia, there is an increase in the level of A1C. The American Diabetes Association (ADA) recommends initiating corrective measures for A1C levels greater than an individualized goal. For example, the presence of several factors including advanced age, history of severe hypoglycemic episodes, and presence of cardio- vascular disease might suggest a glycemic goal of 7.5% to 8%, whereas the absence of these and other worrying factors may mean that a target goal of 6.5% or less is warranted as long as this can be achieved safely. 11

The A1C may overestimate glycemic burden in cer- tain individuals and ethnic groups (such as African Americans). 11 In addition, A1C can be misleading in persons with certain forms of anemia and hemoglobin disorders, and in pregnant women. For these popula- tions, the diagnosis of diabetes must use glucose crite- ria exclusively. Also, the A1C may not be significantly elevated in rapidly evolving diabetes, such as the devel- opment of type 1 diabetes in children. UrineTests The ease, accuracy, and convenience of self-adminis- tered blood glucose monitoring techniques have made urine testing for glucose obsolete for most people with diabetes. These tests only reflect urine glucose levels and are influenced by such factors as the renal threshold for glucose, fluid intake and urine concentration, urine test- ing methodologies, and some drugs. It is recommended that all people with diabetes self-monitor their blood glucose. Urine ketone determinations remain an impor- tant part of monitoring diabetic control, particularly in people with type 1 diabetes who are at risk for develop- ment of ketoacidosis, and in pregnant diabetic women to check the adequacy of nutrition and glycemic control. 28 Diabetes Management The desired outcome of glycemic control in both type 1 and type 2 diabetes is normalization of blood glucose as a means of preventing short- and long-term complications. Treatment plans involve dietary management (medical nutrition therapy), exercise, and antidiabetic agents. People with type 1 diabetes require insulin therapy from the time of diagnosis. Weight loss and dietary manage- ment may be sufficient to control blood glucose levels in people with type 2 diabetes. However, they require follow-up care because insulin secretion from the beta cells may decrease or insulin resistance may persist or worsen, in which case non-insulin agents are prescribed. Among the methods used to achieve these treatment goals are education in self-management and problem solving. Individual treatment goals should take into account the person’s age and other disease conditions, the person’s capacity to understand and carry out the treatment regimen, and socioeconomic factors that might influence compliance with the treatment plan. Optimal control of both type 1 and type 2 diabetes is associated with prevention or delay of chronic diabetes complications. Dietary Management Dietary management usually is individualized to meet the specific needs of each person with diabetes. 11,29 Therapy goals include maintenance of near-normal blood glucose levels, achievement of optimal lipid levels, adequate calories to attain and maintain a reasonable weight, prevention and treatment of chronic diabe- tes complications, and improvement of overall health through optimal nutrition.