Laboratory Tests
Among the various laboratory tests for diabetes, the following three are most common.
Oral Glucose Tolerance Test
An oral glucose tolerance test can be used to confirm a diagnosis of diabetes. The subject fasts for a specific period, after which 75 g of anhydrous glucose dissolved in water is administered. However, rarely is this test necessary in clinical practice because the measurement of elevated fasting plasma glucose done on two separate days should suffice in the diagnosis of diabetes.
Fasting Glucose Levels
Fasting levels can be obtained after an 8-hour fasting period. In a healthy person, the level should be equal to or lower than 110 mg/dl. A higher result indicates impaired glucose homeostasis. Diabetes is diagnosed at a level equal to or greater than 126 mg/dl (7.0 mmol/l). If a blood sugar test is conducted at any time of the day, including after a meal, and the results are equal to or greater than 200 mg/dl (11.1 mmol/l), diabetes is indicated.
Fructosamine and Hemoglobin A1c
A comprehensive dysglycemic metabolic profile also includes fructosamine and hemoglobin A1c (HbA1c). Fructosamine is a good short-term indicator of average glucose levels (10-14 days). It is a measure of how glucose levels are affecting proteins in the blood. Fructosamine is a sensitive marker of a patient’s recent glycemic control, allowing practitioners to monitor treatment effectiveness over a shorter intervention period. High fructosamine levels may also be an important warning signal for increased risk of cardiovascular disease and mortality. Some research has shown a 4.3-fold increase in cardiovascular related deaths for women with high fructosamine levels.
HbA1c measures longer-term blood glucose control over a period of 2 to 3 months. Also known as glycated hemoglobin, HbA1c measures the effects of glucose on red blood cells. Since red blood cells live for an average of 3 months, HbA1c levels reflect average blood glucose levels during a 3-month time period. Thus, HbA1c levels help assess how well an individual is controlling glucose levels on average. As with fructosamine, there is a correlation between HbA1c levels and coronary heart disease risk. Higher levels of HbA1c have also been associated with other debilitating complications of diabetes, such as erectile dysfunction, retinopathy, and neurological disease.
