1. Screening test
Screening tests are performed on people who have no symptoms of diabetes but are at a risk of developing diabetes. These include:
- Blood relatives (mother, father, brother or sister) of people with diabetes.
- Women who have had gestational diabetes or who have had babies weighing 9 pounds or more at birth.
- People with a condition known as impaired glucose tolerance or impaired fasting glucose.
- People with high blood pressure (above 140/90 millimeters of mercury) or very high blood cholesterol levels (such as high density lipoprotein (HDL) less than 35 mg/dl or triglycerides more than 250 mg/dl
- People who are obese i.e. being more than 20% above ideal body weight or having a body mass index (BMI) greater than or equal to 27. BMI is the ratio of weight in kilograms to height in meters square (kg/m2)
- People 45 years or older. Even in the absence of any of the above risk factors they should get the test done every three years.
- Pregnant women should be screened for gestational diabetes (diabetes that starts during pregnancy) between the 24th and 28th weeks in following cases : a. Women 25 years of age or older. b. Women less than 25 years of age and obese. c. Having a family history of diabetes (parent or sibling).
2. Diagnostic test
Diagnosis of diabetes is done on the basis of too-high levels of glucose in the blood. This is done to confirm a diagnosis that is already suspected from the patient’s symptoms. These tests include :
I. Fasting Plasma Glucose Test : The fasting plasma glucose test is the preferred way to diagnose diabetes. After fasting for at least 8 hours, a single sample of your blood is drawn and sent for laboratory analysis. Normal fasting plasma glucose levels are less than 110 milligrams per deciliter (mg/dl). Fasting plasma glucose levels of more than 126 mg/dl on two or more tests on different days indicate diabetes. Blood sample is to be taken ideally in the morning since stress hormone levels rise during the later part of the day elevating the blood glucose levels even though you are fasting.
II. Random Plasma Glucose Test : In this test the blood samples can be taken any time of the day. A blood glucose level of 200 mg/dl or higher indicates diabetes, but it must be reconfirmed on another day with a fasting plasma glucose or an oral glucose test. This is only a screening test and not suitable for adjusting drug dose.
III. Oral Glucose Tolerance Test : For this test, the patient must fast overnight (at least 8 hours but not more than 16 hours) and go to the laboratory in the morning. First, the fasting plasma glucose is tested. After this test, the patient is given 75 grams of glucose (100 grams for pregnant women) dissolved in 300 ml of water. Blood samples are taken 2 hours after the person has consumed the drink.
Glucose tolerance tests may lead to one of the following diagnoses :
- Normal response : A person is said to have a normal response when the 2-hour glucose level is less than 140 mg/dl, and all values between 0 and 2 hours are less than 200 mg/dl.
- Impaired glucose tolerance : A person is said to have IGT when the fasting plasma glucose is less than 126 mg/dl and the 2-hour glucose level is between 140 and 199 mg/dl.
- Diabetes : A person has diabetes when the fasting plasma glucose is 126 mg/dl or greater and the 2-hour glucose level is 180 mg/dl or more.
- Gestational diabetes : A woman has gestational diabetes when she has any two of the following: a fasting plasma glucose of more than 95 mg/dl, a 1-hour glucose level of more than 180 mg/dl, a 2-hour glucose level of more than 155 mg/dl, or a 3-hour glucose level of more than 140 mg/dl.
For the oral glucose tolerance test test to give reliable results it is important that the person :
- Must be in good health (not have any other illness like common cold, fever).
- Must be normally active (for example, not lying down as an inpatient in a hospital).
- Must not be taking any medicines that could affect your blood glucose.
- Must take a diet high in carbohydrates (150-200 grams per day) 3 days before the test.
- Should not smoke or drink coffee on the morning of the test.
IV. Urine test : High urine glucose levels give doctors a clue that something is wrong. But urine tests are not a good way to diagnose diabetes. The level of blood glucose needed to make glucose appear in the urine is different for each person. Your glucose level in blood could be high, yet high levels of glucose may not appear in the urine. Therefore, blood test is more accurate for diagnosing diabetes. On the other hand, urine tests are a very useful way to measure ketones, substances that build up when blood glucose is very high.
3. Monitoring test
Glycosylated hemoglobin test : This test is mainly done to monitor the blood glucose control. It requires only one sample of blood, which can be taken at any time of the day, even right after a meal. Red blood cells have a life of 120 days. Every day a cup of old blood is destroyed and replaced by fresh blood. As the fresh blood emerges into circulation, a percentage of it interacts with blood glucose and forms a type of hemoglobin called glycosylated hemoglobin. Thus the amount of glycosylation is an indicator of the level of blood glucose when that red cell came into circulation. The total blood pool therefore has a mixture of red cells aged 1 day to 90 days. Measuring the average glycosylated hemoglobin (HbA1c) tells us the average blood sugar from the last 90 days (normal value is 4 – 6.5 %).