By Judith Grout
Understanding diabetes lab test results can be crucial in managing the disease. Diabetes is a chronic condition that requires an enormous amount of self-care and that can affect many parts of the body. Because of this, people who have diabetes are generally advised to visit their doctors multiple times a year and also to see various specialists (such as endocrinologists, podiatrists, and eye doctors) periodically to screen for potential problems and treat any complications that arise. Along with blood pressure readings and inspection of the feet and eyes, there are a number of laboratory tests recommended by the American Diabetes Association. These tests are used to track blood glucose control, kidney function, cardiovascular health, and other areas of health.
Although you certainly can’t and won’t be expected to analyze the lab report when your test results come back, knowing a little bit about what your report says can be a way for you to more fully understand and take charge of your health. If it isn’t already your doctor’s regular practice to give you copies of your lab reports, ask for a copy the next time you have lab tests done. Use the information in this article to learn more about what lab reports show, and discuss your results with your doctor to learn what your results mean with regards to your health.
All lab reports share certain standard features, regardless of the test(s) they show. A Federal law, the Clinical Laboratory Improvement Act, regulates all aspects of clinical laboratory testing. It states exactly what information must be included in your lab test report. Some of the standard features include the following:
• Your name and a unique identification number, which may be either your birth date or a medical record number assigned to you by the lab.
• The name and address of the lab that tested your blood, urine, or tissue samples. This lab may be part of a hospital or clinic, or it may be a commercial reference laboratory.
• The names of all authorized persons (such as your doctor) who ordered the test(s) and received the results.
• Specimen type, which may be blood, urine, or a particular type of tissue. If different specimens were used for the same basic type of test (such as testing both blood and urine for glucose), the sample used for each test is indicated.
• A list of all tests performed on each sample.
• Results, which may be expressed as numbers or by the designation of positive or negative. Sometimes both numbers and words may be used to describe the outcome, such as “>100,000 colonies/cc Escherichia coli.” In this example, the symbol for “greater than” is used in describing the number of bacterial colonies per cubic centimeter.
• Abnormal or out-of-range results. These are highlighted or shown in bold print to draw immediate attention.
• Critical results. These highly abnormal results must be reported immediately to your doctor, and the report will include the date and time your doctor was notified.
• The unit of measurement for each test result. This unit may differ from one lab to another; for example, one lab might give a result in milligrams per deciliter while another gives it in millimoles per mole (a mole is a unit widely used in chemistry). But each lab report will also include a reference range in the same unit as each result to help put the number in context.
• Reference ranges, or numbers provided to show how your results compare with those of the “normal” population. The units used to express these ranges, as well as the numbers themselves, will depend on the specific methods and instruments that the lab uses.
(To learn about some terms that are commonly encountered on lab test reports, click here.)
Read your printed report carefully, taking note of any result that is outside the reference range. If you’re not sure about the significance of a particular test or result, don’t hesitate to contact your doctor or clinic or the laboratory where the test was conducted. Make sure to have your lab report in hand when you ask your questions so you can be specific.
Diabetes is a group of metabolic disorders defined by an inability to produce or respond to the hormone insulin, resulting in elevated blood glucose levels. While the bodily processes that lead to different types of diabetes are distinct, most of the tests used to diagnose diabetes do not specify which type is present and can be used interchangeably. The main tests used to diagnose diabetes are the fasting plasma glucose test, the oral glucose tolerance test, and the HbA1c test.
A fasting plasma glucose test is simply a blood glucose test that is conducted when the person has not had any caloric intake for at least eight hours. Using this test, diabetes is defined as a blood glucose level of 126 mg/dl (milligrams per deciliter) or higher. A level between 100 and 125 mg/dl indicates prediabetes, while a level between 70 and 99 mg/dl is considered “normal.” Since conditions other than diabetes (including stress) may elevate blood glucose levels temporarily, a doctor may order a repeat test or a different type of test if the results of a person’s fasting plasma glucose test are borderline or are high in the absence of diabetes symptoms.
The oral glucose tolerance test is more complicated and is used less frequently for diagnosis than the fasting plasma glucose test. For this test, the person drinks a solution containing 75 grams of glucose. Two hours later, a blood glucose level of 200 mg/dl or higher indicates diabetes.
While the HbA1c (hemoglobin A1c, or glycated hemoglobin) test has long been used to evaluate long-term blood glucose control in people with known diabetes, only in 2010 was it approved as a diagnostic test by the American Diabetes Association. An HbA1c level of 6.5% or higher indicates diabetes when the test is used for diagnosis. If a blood glucose reading is like a snapshot, indicating the glucose level at the time of the test, an HbA1c result is like a long-exposure photograph, giving an estimate of the average blood glucose level over the past two to three months.
Type 1 diabetes usually sets in earlier in life and develops rapidly, while Type 2 diabetes usually develops gradually in middle or old age. If your diabetes was diagnosed after age 50, it was probably assumed to be Type 2 without any further testing. Initial treatment for Type 2 diabetes usually involves recommendations for dietary changes, increased physical activity, and the oral diabetes drug metformin. If these measures fail to lower your blood glucose levels, your doctor may order a diabetes-related autoantibody test to check whether Type 2 diabetes may have been the wrong diagnosis.
Autoantibodies are proteins, produced as part of the body’s immune system, that bind to the body’s own tissues and cells as part of an autoimmune attack. Normally, antibodies produced by the immune system attack outside invaders such as bacteria, viruses, pollen, and toxins, but in an autoimmune attack the immune system mistakenly targets cells that are native to the body.
In Type 1 diabetes, the immune system attacks the insulin-producing beta cells of the pancreas. Type 2 diabetes, on the other hand, is mainly caused by the body’s resistance to insulin and doesn’t involve an autoimmune response. Autoantibodies for Type 1 diabetes are present in about 95% of people with the condition. Using the diabetes-related autoantibody test can thus help your doctor distinguish between Type 1 and Type 2 diabetes. If it turns out that you actually have Type 1 diabetes, your doctor will prescribe insulin and probably take you off any oral diabetes drugs.
In some cases, a person with autoantibodies will be determined to have not Type 1 diabetes but LADA, or latent autoimmune diabetes in adults. The criteria for diagnosing LADA are still somewhat controversial, but generally people who have it are adults when they are diagnosed with diabetes, have autoantibodies, and do not immediately need insulin, the way people with Type 1 diabetes do. However, while some people with LADA can use oral diabetes medicines initially to manage their blood glucose levels, all will eventually need to use insulin, and some practitioners believe it is best to start insulin immediately because it may help to preserve the insulin-producing beta cells in the pancreas.
Another, less common type of diabetes is monogenic diabetes, meaning it is caused by a gene mutation. The most common types of monogenic diabetes are maturity-onset diabetes of the young, or MODY, and neonatal diabetes. There are actually several different types of MODY, each caused by a different genetic defect. MODY tends to run in families and to cause symptoms before age 25. If a doctor suspects MODY, a genetic test can confirm it. Treatment varies depending on the specific genetic defect. Neonatal diabetes occurs within the first six months of life and can often be treated with oral drugs rather than insulin.
Portable blood glucose meters are what enable people with diabetes to see the effects of their past actions and make decisions about future ones, particularly in the areas of food, exercise, and insulin injections. These devices use a blood sample from a fingertip (or sometimes from another part of the body, such as the palm or forearm), which is applied to a test strip and inserted in the meter to produce a result in seconds.
To get the most accurate readings from your meter, it’s important to follow all of the recommended steps for obtaining a blood sample and applying it to the test strip. That includes washing your hands before lancing a finger, since even a tiny amount of food residue on your finger can lead to a high blood glucose reading. It’s also a good idea to test the meter itself periodically with the control solution provided by the meter manufacturer.
Sometimes a physician will order a fasting plasma glucose test to evaluate a person’s diabetes treatment plan. If yours does, you can use it as an opportunity to compare your diabetes lab test meter results to the laboratory glucose test by monitoring (using blood from your finger) just before you have blood drawn. (You’ll then need to keep a record of that result until you get your lab results back.) Because the blood samples used in portable meters are taken from capillaries, and the blood samples used for laboratory tests are taken from veins, the two tests will produce slightly different results, even when the samples are taken within seconds of each other. Compared with laboratory tests, portable blood glucose meters have an accuracy level of ±20%. This means that if your laboratory result is 100 mg/dl, your meter result may be anywhere from 80 mg/dl to 120 mg/dl.
While self-monitoring is important for daily decision-making and for detecting patterns, the most important lab test for evaluating long-term blood glucose control is the HbA1c test. This test measures the percentage of hemoglobin A — a molecule in red blood cells that transports oxygen — that is attached to glucose. When hemoglobin A is bound to glucose, it is said to be glycated (or glycosylated), and it remains so for the life of the cell. Red blood cells remain in circulation for about 120 days, and then they are replaced by new, nonglycated red blood cells. So measuring glycated hemoglobin A, or HbA1c, is an excellent way to evaluate your blood glucose control over the past 120 or so days.
HbA1c results are currently reported in the United States as a percentage. The goal for most people with diabetes, as recommended by the American Diabetes Association, is to maintain a level below 7%. Your lab report may also show a result in millimoles per mole (mmol/mol), along with an estimated average glucose level (eAG) expressed in milligrams per deciliter. Rather than being a separate measurement, an eAG is simply an approximation based on your HbA1c level. In reality, the relationship between average blood glucose level and HbA1c is not exact; two people with the same average glucose level can have different HbA1c levels, and the relationship between average glucose level and HbA1c can vary over time even within the same person. But because the eAG is expressed in the same units used by your blood glucose meter, it can make your HbA1c level more readily understandable.
In some people, measuring HbA1c may not be useful. Reliable HbA1c testing depends on red blood cells being composed mostly of hemoglobin A. Problems arise when another type of hemoglobin predominates, such as hemoglobin S in the case of sickle cell anemia. Ruptured red blood cells, excessive hemorrhaging, pregnancy, recent blood transfusions, and iron deficiency can also make the HbA1c test undependable.
Fortunately for these cases, glucose is also attracted to proteins in the blood. When glucose attaches to a protein molecule, the combination forms fructosamine, also known as glycated serum protein. Proteins remain in the bloodstream for two to three weeks, so the test shows your blood glucose control over the previous two to three weeks. Measuring fructosamine can also be a useful option when you’re just starting or have recently modified your diabetes treatment plan. Just as with HbA1c, a high fructosamine level indicates that blood glucose has been elevated, and a normal fructosamine level indicates good blood glucose control.
If your blood glucose or insulin level is so low that your body cannot use glucose as an energy source, the body mobilizes another source of energy: fats. The breakdown of fats produces ketones, chemicals that in low concentrations are harmless but in higher concentrations can disrupt the body’s acid–base balance. The combination of low insulin levels, high blood glucose, and dehydration is called diabetic ketoacidosis (DKA), and it is a medical emergency.
The measurement of ketones is not a part of routine laboratory testing, but you can test your urine or blood for ketones at home, and if you were to arrive in the emergency room with symptoms of DKA, the ER physician would immediately order a ketone test. (Only certain home meters can test for blood ketones.)
Symptoms of ketoacidosis, which tends to develop over several days, include excessive thirst, frequent urination, rapid breathing, nausea, and dehydration. The breath may also develop a fruity odor from ketones entering the lungs from the bloodstream. It occurs most commonly in people with Type 1 diabetes when their insulin levels are too low, but it can develop in people with any type of diabetes, especially when they are sick. If you have symptoms of DKA, you should call your physician immediately.
The American Diabetes Association recommends that most adults with diabetes who are not taking cholesterol-lowering statins have a fasting lipid profile done at diagnosis, first medical evaluation, and every five years thereafter, while those taking statins should have the test done when they start the medicine and periodically thereafter. This test measures HDL (high-density lipoprotein, or “good”), LDL (low-density lipoprotein, or “bad”), and total cholesterol, as well as the level of triglycerides in the blood. HDL cholesterol above 40 mg/dl for men and 50 mg/dl for women, LDL cholesterol below 100 mg/dl, and triglycerides below 150 mg/dl are levels considered to pose a low risk of cardiovascular problems. Recent research shows that for people with diabetes, meeting the guidelines for blood pressure and cholesterol control are more important than meeting the guidelines for blood glucose control in preventing cardiovascular disease.
Diabetic nephropathy (kidney disease related to diabetes) is the leading cause of kidney failure in the United States, and it can develop in people with either Type 1 or Type 2 diabetes (as well as in those with rarer types of diabetes). But signs of kidney dysfunction develop long before kidney failure sets in. And when diminished kidney function is detected early, steps can be taken to stop or slow any progression.
This is why the American Diabetes Association recommends that people who have had Type 1 diabetes for at least five years undergo an annual test for albumin in their urine, that people with Type 2 diabetes undergo this test at diagnosis and annually thereafter, and that everyone with diabetes and high blood pressure have this test annually. Albumin is a protein that leaks into the urine when kidney function is diminished.
In addition, these people should have their blood creatinine level measured at least once a year. Creatinine is a by-product of normal muscle breakdown whose level in the blood can be used to estimate the glomerular filtration rate (GFR) of the kidneys. A GFR of 90 ml/min/1.73 m2 (milliliters per minute per 1.73 square meters) or higher is considered indicative of normal kidney function unless other evidence is present (such as albumin in the urine). In that case, even with a “normal” GFR, a person is considered to have Stage 1 kidney disease. A GFR of 60–89 indicates Stage 2 kidney disease, 30–59 indicates Stage 3, and 15–29 indicates Stage 4. A GFR below 15 indicates Stage 5 (end-stage) disease, or kidney failure. Each stage of chronic kidney disease requires taking different steps to manage the condition. However, at any stage — including before kidney disease begins — its development or progression can be slowed through blood glucose and blood pressure control.
Thousands of laboratory tests are now available to assist in the diagnosis and treatment of diseases; according to the American Society for Clinical Pathology, “laboratory test results may influence up to 70 percent of medical decision making.” Understanding why a lab test is prescribed, what its results mean, and how those results inform medical decisions can help you forge a cooperative partnership with your health-care team. The more you know about your health, the more power you have to ensure that your future remains a healthy one.
Want to learn more about the HbA1c diabetes lab test and what it measures? Read “H-B-A-1-C: What It Is and Why It Matters” and “What Does A1C Stand For?”
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