Diagnosis of Diabetes

How Lab Tests Show You Have Diabetes You just found out you have diabetes. If you're like many people, the news makes your head spin. How does the doctor know? How do blood tests help diagnose the disease? Could the test results be wrong? Is more than one test needed? Should your family members have tests, too? To understand how doctors diagnose diabetes, read on. High Blood Glucose Levels Doctors diagnose diabetes on the basis of too-high levels of glucose in the blood. If you have diabetes, your blood glucose levels rise because of the foods you eat. Foods have little effect on blood glucose in people without diabetes. Normally, insulin, a hormone that is made in the pancreas, allows glucose to enter your body's cells and be used as fuel. Insulin also makes the liver store excess glucose in the form of glycogen until it is needed. Insulin is the main tool your body uses to lower your blood glucose level. People with diabetes can have insulin deficiency (they make too little insulin) or insulin resistance (their bodies don't respond well to insulin). Some people have a combination of the two. In people with diabetes, insulin is not doing its job, so glucose can't get into the cells to be used for energy. Instead, the unused glucose builds up in the blood and, if high enough, passes through the kidneys. If a person's blood glucose level rises high enough, the extra glucose causes frequent urination. This in turn leads to thirst, as the body tries to make up for the fluid lost in urination. What Urine Tests Measure High urine glucose levels give doctors a clue that something is wrong. But urine tests are not a good way to diagnose diabetes. Urine tests are not as accurate as blood tests. And the level of blood glucose needed to make glucose appear in the urine is different for each person. Your glucose level could be high, yet high levels of glucose may not appear in the urine. So in diagnosing diabetes, doctors measure glucose in the blood. (Urine tests are a very useful way to measure ketones, substances that build up when blood glucose is very high. Because ketones are acids that are toxic to the body, they are flushed out in urine quickly.) Blood Tests The goal of blood glucose tests is to find out whether you have a very large amount of glucose in your blood. There are two types of tests, screening tests and diagnostic tests. Screening tests are performed on people who have no symptoms of diabetes. On the other hand, diagnostic tests are done to confirm a diagnosis that is already suspected from the patient's symptoms. Screening tests are fast, easy to perform, and cheap. (Health fairs often offer screening tests, for example.) Screening tests require as little as a drop of blood from your fingertip and take only a minute or two to complete. Most doctors don't screen everyone for diabetes during regular checkups. The chance of finding the disease in most people is just too low. But screening tests are useful for people who may be at risk for developing diabetes. People at risk include: Blood relatives of people with diabetes. Women with unexplained miscarriages or stillbirths or who have had babies weighing 9 pounds or more at birth. People with a condition known as "impaired glucose tolerance" (see Oral Glucose Tolerance Test below). People with high blood pressure or very high blood cholesterol or triglyceride levels. People who are obese. People over age 65. All pregnant women should be screened for gestational diabetes (diabetes that starts during pregnancy) between the 24th and 28th weeks. Having a screening test every three years is often enough as long as the results are normal. If you have an abnormal screening test result, you should have a diagnostic test. For diagnostic tests, the doctor's office draws one or more samples of blood from a vein and sends them to a lab for analysis. When you get your test results, ask your doctor to explain them to you. Comparing your test results with those of family or friends may confuse or alarm you. You may not have had the same type of test, and so your results could have a completely different meaning. You should ask your doctor to explain your results to prevent any confusion. Several types of diagnostic tests are commonly used to diagnose diabetes. Fasting Plasma Glucose Test The fasting plasma (blood) glucose test is a reliable way to diagnose diabetes. It is easy to perform, and age, physical activity, and calorie intake have little effect on the results. After you have fasted overnight (10 to 16 hours), the doctor's office draws a single sample of your blood and sends it to the lab for analysis. Normal fasting plasma glucose levels are less than 6.0 millimoles per litre (mmol/L). Fasting plasma glucose levels of more than 7.0 mmol/L on two or more tests indicate diabetes, and you need no other tests. Random Plasma Glucose Test Sometimes, random blood samples reveal a blood glucose level so high (more than 11.1 mmol/L) that there is no doubt the person has diabetes -- if he or she also has symptoms of the disease. A random plasma glucose between 7.8 mmol/L and 11.1 mmol/L taken after you've eaten is not necessarily abnormal. Problems in interpreting blood glucose tests can come up when levels are not clearly normal or abnormal. If this situation occurs, your doctor may order a glucose tolerance test. Oral Glucose Tolerance Test With the oral glucose tolerance test, you must fast overnight (at least 10 but not more than 16 hours) and go to your doctor's office or the lab in the morning. First, your fasting plasma glucose is tested. After this test, you receive 75 grams of glucose. Usually, the glucose is in a sweet-tasting liquid that you drink. Blood samples are taken 1 hour and 2 hours to measure your blood glucose. For the test to give reliable results, you must be in good health (not have any other illnesses, not even a cold). Also, you should be normally active (for example, not lying down as an in-patient in a hospital) and taking no medicines that could affect your blood glucose. For three days before the test, you should have eaten a diet high in carbohydrates (150 to 200 grams per day). The morning of the test, you should not smoke or drink coffee. During the test, you need to lie or sit quietly. The oral glucose tolerance test measures blood glucose levels five times over a period of 2 hours. In a person without diabetes, the glucose levels rise and then fall quickly. In someone with diabetes, glucose levels rise higher than normal and fail to come back down as fast. People with levels in between normal and diabetic may be classified as having impaired glucose tolerance (IGT). People with IGT do not have diabetes. It is wrong to say they are pre diabetic, latent diabetic, or chemical diabetic. Each year, only 1 to 5 percent of people whose test results show IGT actually develop diabetes. And with re-testing, as many as half of people with IGT have normal oral glucose tolerance test results. Weight loss and exercise may help people with IGT return their glucose levels to normal. As with fasting or random blood glucose tests, a markedly abnormal oral glucose tolerance test is diagnostic of diabetes. But blood glucose responses during the oral glucose tolerance test can vary somewhat. For this reason, if a test shows that you have mildly high blood glucose levels, the doctor should run the test again to make sure the diagnosis is correct. Glucose tolerance tests may lead to one of the following diagnoses. Normal response. A person is said to have a normal response when the fasting glucose level is less than 7.0 mmol/L and the 2-hour glucose level is less than 7.8 mmol/L. Impaired glucose tolerance. A person is said to have IGT when the fasting plasma glucose is less than 7.0 mmol/L, the 2-hour glucose level is between 7.8 and 11.1 mmol/L. Diabetes. A person has diabetes when glucose tolerance test show that the blood glucose level at fasting is 7.0 mmol/L or more or the 2 hour level is more than 11.1 mmol/L. In diagnosing your diabetes, your doctor needed test results. But test results are just part of the information that goes into the diagnosis of diabetes. Your doctor also took into account your physical exam, symptoms, and medical history in order to decide to test. The Blood Test With A Memory Once you've been diagnosed with diabetes, your doctor may order another type of blood test called glycated haemoglobin or glycohaemoglobin (GHb). This test is easy to do during routine office visits. GHb lets the doctor take a backward look at your diabetes control. Haemoglobin is the protein in red blood cells that carries oxygen. GHb forms when glucose in the blood attaches to the haemoglobin. Because blood cells stay in circulation for three to four months, GHb level is a good measure of a person's average blood glucose level over the previous three to four months. The HbA1c test requires only one sample of blood, which can be taken at any time of the day, even right after a meal. Although a high HbA1c almost always means IGT or diabetes, people with IGT or diabetes can have normal HbA1c levels. So the HbA1c test is not used to diagnose diabetes. Doctors use it to monitor blood glucose control. Type 1 or Type 2? After the diagnosis of diabetes, the doctor will take many factors into account to determine which type of diabetes you have. In general, people with type 1 are diagnosed when they are under 30 years old, lean, and have had diabetic ketoacidosis (which sometimes lead to a coma) or have high levels of ketones in their urine. People with type 2 are most often diagnosed when they are over 30 and obese. They usually do not have urine ketones. Of course, there are exceptions to these categories. Whatever type you have, the goal of treatment is to get your blood glucose levels as close to normal as possible.