Steve V. Edelman, MD
Robert R. Henry, MD
Certain key clinical and metabolic parameters should be monitored during office visits:
- To assess glycemic control:
- A1C level
- Plasma glucose values
- To assess CV risk:
- Lipoprotein analysis
- Blood pressure
- Body weight
- To assess for evidence of diabetic complications:
- Kidney test
- Dilated eye examination
- Foot examination.
The metabolic goals for these parameters are shown in Table 13.1.
Glycemic control is assessed during office visits with determinations of plasma glucose levels and assays for glycated hemoglobin. Patients can evaluate the effects of their treatment regimen on a day-to-day basis between office visits by using SMBG at home. A combination of physician and patient assessment methods are used to obtain the most accurate information about the degree of metabolic control.
Measuring Plasma Glucose Concentrations
Day-to-day glycemic control is reflected in measurements of plasma glucose concentrations. However, because this measurement is an isolated finding at a single point in time, it may not represent a patient’s usual metabolic state. Some limitations of plasma glucose measurements include the following:
- It is difficult to know the meaning of a single random or fasting plasma glucose determination.
|TABLE 13.1 — Metabolic Goals of Effective Management
• Glycosylated hemoglobin:
– Within 1% point above the upper range of normal (7%)
– Within 3 SD from the mean
|• FPG level between 80 mg/dL and 120 mg/dL|
|• 2-hour postprandial plasma glucose level|
|• Systolic/diastolic blood pressure <130/85 mm Hg if no evidence of proteinuria (<120/80 mm Hg with evidence of proteinuria)|
|• Approach or maintain ideal body weight|
• Lipoprotein goals:
– Triglyceride level
– HDL cholesterol level >45 mg/dL (>55 in women)
– LDL cholesterol level
- Random determinations may reflect peak, trough, or values in between because of the wide daily variations in glucose levels.
- The stress of an office visit may result in higher than usual glucose values.
- Some patients may become atypically adherent to their treatment regimen or use extra insulin before an office visit, resulting in an uncharacteristically low glucose level.
- The presence of an intercurrent illness at the time of an office visit can alter blood glucose levels.
The timing of plasma glucose measurements has an impact on the significance of the findings:
- A postprandial sample obtained 1 to 2 hours after a patient has eaten is the most sensitive measurement because glucose levels are the highest during this time; total carbohydrate content of the meal will be reflected in this glucose value.
- A preprandial or fasting plasma glucose level reflects how efficiently carbohydrates from a meal have been cleared from the plasma.
Measuring Glycated Hemoglobin
Assays of HbA1, A1C, and glycated hemoglobin are used extensively to provide an accurate time-integrated measure of average glycemic control over the previous 2 to 3 months and to correlate plasma glucose measurements and patients’ SMBG results. Because these assays do not reflect the glucose level at the time a blood sample is tested, measurements of glycated hemoglobin are not useful for making day-to-day adjustments in the treatment regimen.
Glycation refers to a carbohydrate-protein linkage. This irreversible process occurs as glucose in the plasma attaches itself to the hemoglobin component of red blood cells. Because the life span of red blood cells is 120 days, glycated hemoglobin assays reflect average blood glucose concentration over that time.
The amount of circulating glucose concentration to which the red cell is exposed influences the amount of glycated hemoglobin. Therefore, the hyperglycemia of diabetes causes an increase in the percentage of glycated hemoglobin in patients with diabetes; A1C shows the greatest change, whereas the remaining glycated hemoglobins are relatively stable.
Levels of A1C and HbA1 correlate best with the degree of diabetic control obtained several months earlier. Regardless of which assay is used, however, certain conditions can interfere with obtaining accurate results:
- False low concentrations are likely in the presence of conditions that decrease the life ofthe red blood cell, such as:
- Hemolytic anemia
- Sickle cell trait
- False high concentrations are likely in the presence of conditions that increase the lifespan of the red blood cell, e.g., patients without a spleen. Other conditions that producefalsely elevated glycated hemoglobins include:
- High concentrations of fetal hemoglobin
- High aspirin doses (>10 g/day)
- High concentrations of ethanol.
A disposable test kit for glycosylated A1C is now available for home testing by patients with diabetes (Click here for A1cTest.com.)
Next Week, Measuring Other Glycated Proteins and Self-Monitoring of Blood Glucose
You can purchase this text at Amazon.com, just click on this link: Diagnosis and Management of Type 2 Diabetes 10E
American Diabetes Association. Standards of medical care in diabetes — 2010. Diabetes Care. 2010;33(suppl 1):S11-S61.
American Diabetes Association. Medical Management of Non–insulin-dependent (Type II) Diabetes. 3rd ed. Alexandria, VA: American Diabetes Association; 1994:52-54.
Buckingham B, Caswell K, Wilson DM. Real-time continuous glucose monitoring. Curr Opin Endocrinol Diabetes Obes. 2007;14:288-295.
Fleming DR. Accuracy of blood glucose monitoring for patients: what it is and how to achieve it. Diabetes Educ. 1994;20:495-500.
© Copyright 2010. Steven V. Edelman, MD, Robert R. Henry, MD, Professional Communications, Inc. All rights reserved.