Diagnosis of diabetes
In diagnosing diabetes, physicians primarily depend upon the results of specific glucose tests. However, test results are just part of the information that goes into the diagnosis of diabetes. Doctors also take into account your physical exam, presence or absence of symptoms, and medical history. Some people who are significantly ill will have transient problems with elevated blood sugars which will then return to normal after the illness has resolved. Also, some medications may alter your blood glucose levels (most commonly steroids and certain diuretics (water pills)). The two main tests used to measure the presence of blood sugar problems are the direct measurement of glucose levels in the blood during an overnight fast, and measurement of the body’s ability to appropriately handle the excess sugar presented after drinking a high glucose drink.
The diagnosis of diabetes in an asymptomatic subject should never be made on the basis of a single abnormal blood glucose value. For the asymptomatic person, at least one additional plasma/blood glucose test result with a value in the diabetic range is essential, either fasting, from a random (casual) sample, or from the oral glucose tolerance test (OGTT). If such samples fail to confirm the diagnosis of diabetes mellitus, it will usually be advisable to maintain surveillance with periodic re-testing until the diagnostic situation becomes clear. In these circumstances, the clinician should take into consideration such additional factors as ethnicity, family history, age, adiposity, and concomitant disorders, before deciding on a diagnostic or therapeutic course of action. An alternative to blood glucose estimation or the OGTT has long been sought to simplify the diagnosis of diabetes. Glycated haemoglobin, reflecting average glycaemia over a period of weeks, was thought to provide such a test.
How are diabetes and pre-diabetes diagnosed?
The following tests are used for diagnosis:A fasting plasma glucose test measures your blood glucose after you have gone at least 8 hours without eating. This test is used to detect diabetes or pre-diabetes.An oral glucose tolerance test measures your blood glucose after you have gone at least 8 hours without eating and 2 hours after you drink a glucose-containing beverage. This test can be used to diagnose diabetes or pre-diabetes.In a random plasma glucose test, your doctor checks your blood glucose without regard to when you ate your last meal. This test, along with an assessment of symptoms, is used to diagnose diabetes but not pre-diabetes.Positive test results should be confirmed by repeating the fasting plasma glucose test or the oral glucose tolerance test on a different day.
What are the new diagnostic criteria?
The new WHO criteria for diagnosis of diabetes mellitus and hyperglycaemia. The major change from the previous WHO recommendation is the lowering of the diagnostic level of fasting plasma glucose to 7.0 mmol/L, from the former level of 7.8 mmol/L. For whole blood, the proposed new level is 6.1 mmol/L, from the former 6.7 mmol/L.
This change is based primarily on cross-sectional studies demonstrating the presence of microvascular and macrovascular complicationsat these lower glucose concentrations. In addition, the 1985 WHO diagnostic criterion for diabetes based on fasting plasma glucose level (7.8 mmol/L) represents a greater degree of hyperglycaemia than the criterion based on plasma glucose level two hours after a 75 g glucose load (11.1 mmol/L). A fasting plasma glucose level of 7 mmol/L accords more closely with this 2 h post-glucose level.
