Proinsulin (Blood) Does this test have other names? No. What is this test? This blood test measures proinsulin, a building block for insulin. To turn food into energy, your pancreas makes proinsulin. Proinsulin, in turn, is made into insulin and another protein called C-peptide. Problems making insulin can lead to diabetes. In type 1 diabetes, your pancreas becomes damaged and has trouble making or controlling the amount of insulin in your body. In type 2 diabetes, the more common type, your body becomes resistant to the insulin you make. Your body may also not be able to regulate the amount of insulin you make because of a tumor or a problem with your pancreas. Measuring proinsulin in your blood can help figure out your risk for type 1 or type 2 diabetes. People with type 1 and type 2 diabetes may have levels of proinsulin that are higher than normal. Proinsulin levels are also usually high in later stages of type 2 diabetes, and this test can help your doctor decide which treatment is best for you. Why do I need this test? You may have this test to see how much proinsulin your body is able to make. This helps your doctor find out your risk for diabetes. High levels of proinsulin have also been linked to heart and artery disease. Your doctor may want to watch you for heart disease if your proinsulin levels are high. You may also have this test if your doctor suspects you have hypoglycemia, or low blood sugar. This is when your blood sugar level falls below 50 milligrams per deciliter. This can cause: Uncontrollable shaking Confusion Sweating Heart palpitations Headache Blurry vision What other tests might I have along with this test? Your doctor may also order a C-peptide test at the same time as the proinsulin test. If you have C-peptide in your blood, it means your body is making insulin. Checking your C-peptide level helps your doctor figure out if you have type 1 or type 2 diabetes. If you have low C-peptide levels you may have type 1 diabetes. People with type 2 diabetes usually have normal or high levels of C-peptide. Your blood may also be tested for: Insulin Sulfonylureas, or certain other medicines used to lower blood sugar in people with type 2 diabetes Blood sugar level after eight hours of fasting, called a fasting glucose test A1C level, which can be used to diagnose diabetes Beta-hydroxybutyrate, a type of ketone found in the blood What do my test results mean? Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider. Results are given in picomoles per liter (pmol/L). A normal proinsulin level is 2 to 6 pmol/L. Your doctor may compare your proinsulin and C-peptide levels together. A normal C-peptide result is in the range of 0.5 to 2 nanograms per milliliter. How is this test done? The test requires a blood sample, which is drawn through a needle from a vein in your arm. Does this test pose any risks? Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. What might affect my test results? Your blood sugar level may affect your results. How do I prepare for the test? You may need to fast overnight before you take the test, although the fasting time period before the test varies. Your doctor will give you instructions on how and when to fast. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use. Medical Reviewers: Hanrahan, John, MD Taylor, Wanda, RN, Ph.D.