DIAGNOSIS: 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 is the main tool your body uses to lower your blood glucose level. People with diabetes can have insulin deficiency which means (they make too little insulin) or insulin resistance, which means they don’t respond well to insulin. In people with diabetes, insulin is not doing its job, so their body’s glucose can’t get into their cells and be used for energy. Instead, their unused glucose builds up in their blood and passes through the kidneys if the glucose level becomes high enough. The extra glucose causes frequent urination, which in turn leads to thirst (this is the body’s way of making 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.                                                                                                                                   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 who have had gestational diabetes or who have had babies weighing 9 pounds or more at birth • African Americans, Hispanic Americans, Asian Americans, Native Americans, and Pacific Islanders • people with a condition known as impaired glucose tolerance or impaired fasting glucose (see below) • people with high blood pressure or very high blood cholesterol or triglyceride levels • people who are obese  • people 45 years or older Pregnant women should be screened for gestational diabetes (diabetes that starts during pregnancy) between the 24th and 28th weeks if they are 25 years of age or older, less than 25 years of age and obese, if they have a family history of diabetes (parent or sibling), or if they are a member of an ethnic/racial group at high risk for diabetes (Hispanic-American, Native American, Asian-American, African-American, or Pacific Islander). If you are 45 years or older, have your blood glucose level checked every 3 years. If you have risk factors, you may need to be tested more often. For diagnostic tests, the doctor’s office draws samples of blood from a vein and sends them to a laboratory for analysis. Different types of diagnostic tests are used to diagnose diabetes—fasting plasma glucose, random plasma glucose, and oral glucose tolerance tests. 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, so your results could have a completely different meaning.                                                                                                                                                     Fasting Plasma Glucose Test The fasting plasma glucose test is the preferred way to diagnose diabetes. It is easy to perform and convenient. After you have fasted overnight (at least 8 hours), a single sample of your blood is drawn at the doctor’s office and sent to the laboratory for 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.

                                                                                                  Random Plasma Glucose Test Sometimes, random blood samples (if taken shortly after eating or drinking) may be used to test for diabetes when symptoms are present. 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.                                                    Oral Glucose Tolerance Test With the oral glucose tolerance test, you must fast overnight (at least 8 but not more than 16 hours) and go to your doctor’s office or the laboratory in the morning. First, your fasting plasma glucose is tested. After this test, you receive 75 grams of glucose (100 grams for pregnant women). Usually, the glucose is in a sweet-tasting liquid that you drink. Blood samples are taken up to four times 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 inpatient in a hospital) and taking no medicines that could affect your blood glucose. For 3 days before the test, you should have eaten a diet high in carbohydrates (150–200 grams per day). The morning of the test, you should not smoke or drink coffee.  The oral glucose tolerance test measures blood glucose levels five times over a period of 3 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 glucose levels between normal and diabetic have impaired glucose tolerance (IGT). People with IGT do not have diabetes. Each year, only 1–5% of people whose test results show IGT actually develop diabetes. And with retesting, as many as half of the 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. If your values are abnormal, you will need to have another test—preferably the fasting plasma glucose test. 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 two diagnostic tests done on different days show that the blood glucose level is high.                                                                                                                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. 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 examination, symptoms, and medical history to decide to test.                                                                                                               The Blood Test With a Memory When you’ve been diagnosed with diabetes, your doctor may order another type of blood test called glycated hemoglobin. This test is easy to do during routine office visits. GHb lets the doctor take a backward look at your diabetes control. Hemoglobin is the protein in red blood cells that carries oxygen. GHb forms when glucose in the blood attaches to the hemoglobin. Because blood cells stay in circulation for 2–3 months, GHb level is a good measure of a person’s average blood glucose level over the previous 2–3 months. The GHb 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 GHb almost always means IGT or diabetes, people with IGT or diabetes can have normal GHb levels. So the GHb 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 before they are 30 years old, are lean, and have had diabetic ketoacidosis (which sometimes leads 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.