By Dr Ananya Mandal, MD
Diabetes is diagnosed using tests to assess blood glucose levels. The basic problem in diabetes is the presence of high levels of sugar in the blood and urine which leads to various complications.
Outline of diagnosis
The following steps are usually taken in the process of diagnosing diabetes:
If a patient presents with symptoms of diabetes, a blood test is performed to check the blood glucose level. Sometimes, in the absence of symptoms, a high blood sugar may be detected by routine blood tests performed as part of a general health check-up. An early diagnosis often helps prevent or delay the onset of complications associated with type 2 diabetes.
A random blood sugar test is performed. Diabetes is diagnosed on the basis of a single abnormal plasma glucose reading. When taken randomly at any time of the day, the levels are considered high if they are 11.1 mmol/L or higher.
A fasting blood sugar test may be performed. This is usually taken after an overnight fast. A blood glucose level of 7 mmol/L (126 mg/dL) or higher is considered positive for diabetes when other diabetic symptoms such as thirst, increased urination, recurrent infections, weight loss or drowsiness are present.
A postprandial blood sugar test is performed to check what the blood glucose level is two hours after a full meal has been eaten.
Another test called the oral glucose tolerance test involves a patient fasting, usually overnight, and then ingesting a 75 g dose of glucose. Blood sugar is assessed two hours later and if the plasma glucose level is 11.1 mmol/L or higher, diabetes is diagnosed.
A glycated haemoglobin (HbA1c) test is used to assess a person's blood sugar control in the previous three months. If there are wide fluctuations in blood sugar during this period, the HbA1c level is raised. The test is used both for diagnosing diabetes and monitoring blood sugar control in patients who already have a diabetes diagnosis.
An HbA1c of 48 mmol/mol (6.5%) is the cut-off point for diagnosing diabetes. A value less than 6.5%, however, does not exclude a diabetes diagnosis being made using other blood glucose tests.
In healthy people, urine does not contain glucose but the urine passed by diabetic individuals may contain glucose.
A diagnosis of diabetes also involves checking the eyes, kidneys and heart for signs of the complications associated with long-standing diabetes.
Reviewed by Sally Robertson, BSc
Last Updated: Nov 18, 2013