Diabetes diagnostic tests.
Diabetes diagnosis is bases on certain symptoms, medical and family history, body mass index, clinical examination and tests. In this page you can find information about  the blood laboratory tests that may be required for diagnosis of diabetes.
 Random plasma glucose test. This the easiest test for diabetes. Random plasma glucose test is mainly used to monitor the control of blood glucose level and less for diagnostic purposes. The good thing is that no preparation is required and a single drop of blood, usually taken from a finger, is enough for the test to be done. As the name indicates the blood sample can be taken at any time during the day. A figure which is less than 200mg/dL is considered normal.
Screening glucose challenge test. This test is not enough to establish a secure diagnosis. It can be done to give a first idea about the possibility for the person to suffer from diabetes. Screening glucose challenge test is usually applied in pregnant women and gives information regarding potential occurrence of gestational diabetes. The procedure of the test is quite straightforward and there is no need for any preparation. A sweet liquid, which is a 50gr glucose solution, is given to the person and after one hour a blood sample is taken. Laboratory analysis will show whether the level of glucose in the blood is normal or not. Further investigation may be needed, if the result is 180mg/dL or higher. For many experts this limit should be 140 mg/dL, especially if the woman is overweight or there is a hereditary background.
Fasting plasma glucose test (FPG). This test is required for people being in high risk to be diagnosed with diabetes. A doctor will determine the risk factors based on hereditary background, medical history, age and physical condition. As the name indicates fasting plasma glucose test can give information about the concentration of glucose in plasma after a certain period of abstinence from any food or drink, apart from water. The test requires a minimum fasting period of eight hours. After that, a blood sample is taken for laboratory examination. The blood sample is preferably taken in the morning. The results will show if a person suffers from diabetes or he/she is at a prediabetes stage. If the figure is between 100 and 125mg/dL, more investigation or monitoring is needed, since this is an indication of prediabetes or potential diabetes. In cases that measurements of fasting plasma glucose exceed the level of 125mg/dL, the FPG will be repeated another day. Similar results in the second test mean that diabetes has been already established.
Oral glucose tolerance test (OGTT). Oral glucose tolerance test is another test that can determine whether a person suffers from diabetes, prediabetes, gestational diabetes or reactive hypoglycemia. Although this test is the most complex, it is the most accurate for diagnosis of diabetes. For the patient it is quite unpleasant, since it requires more that one blood samples to be taken. However, oral glucose tolerance test is preferred, because it gives reliable information regarding the ability of our body to metabolize glucose properly. OGTT is recommended for any person who presents signs and symptoms of diabetes or is at risk to suffer the disease. In pregnant women, the oral glucose tolerance test is the next diagnostic step, when the screening glucose challenge test gives figures higher than normal.
Oral glucose tolerance test gives safer results, when it is performed in the morning. The person must be in reasonably good health. If there is any illness, including flue, minor or serious infection and any problem that needs outpatients care or hospitalization, the results will not be accurate.
The preparation stage requires diet high in carbohydrates for the three days preceding the examination. This diet should provide 150-200gr of sugar per day. A fasting period from eight to sixteen hours is required and no smoking or any beverage is allowed prior to the test.
When time comes, the person is given a glucose solution to drink. This solution is nearly 250ml of water containing an amount of glucose equal to 1.75gr per kilogram of the person’s body weight. In any case, the total glucose quantity should not exceed the 75gr. Some experts recommend 100gr for pregnant women. The beverage should be drunk within no more than five minutes. As soon this is done, a first blood sample is taken, followed by another one in two hour’s time. This is the typical procedure for diagnosis of diabetes, prediabetes or gestational diabetes. In pregnant women, blood samples may be taken within one, two and three hours from the glucose intake.
A more comprehensive OGTT aiming to diagnosis of reactive hypoglycemia and other conditions, such as acromegaly, may require more samples taken every half an hour. However, the results taken from the very first (fasting) and the two-hours samples are the most important.
In cases that results of oral glucose tolerance test give indications of any pathological state, the test must be repeated a few days later. If the results are verified by a second or third OGTT, the diagnosis is secured.
The fasting blood glucose results that may indicate a problem or not are the following:
| Fasting Blood Glucose |
Posible Diagnosis |
| 70-99mg/dL |
Normal levels |
| 100-125mg/dL |
Prediabetes or Impaired fasting glucose |
| Higher than 125mg/dL |
Diabetes |
The oral glucose tolerance test results taken from the two-hour blood sample can be:
| Oral Glucose Tolerance |
Posible Diagnosis |
| Up to 139mg/dL |
Normal levels |
| 140-199mg/dL |
Prediabetes or Impaired fasting glucose |
| Higher than 199mg/dL |
Diabetes |
In pregnant women and after the intake of 100gr of glucose the normal OGTT results are:
| Fasting glucose level |
95mg/dL |
| Within one hour after the clucose intake. |
180mg/dL |
| Within two hours after the clucose intake. |
155mg/dL |
| Within three hours after the clucose intake. |
140mg/dL |
Gestational diabetes diagnosis will be established only if at least two of the above limits are exceeded.
Note: The OGTT figures above are the most typically used. However, they may vary, depending on the laboratory.
For more information about the diagnosis of diabetes see Additional Diabetes Tests page.
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