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Blood Glucose



Healthcare providers often order fasting blood glucose tests to screen for diabetes. Since eating food affects blood sugar, fasting blood glucose tests show a more accurate picture of your baseline blood sugar.




blood glucose



The most common use of a blood glucose test is to screen for Type 2 diabetes (T2D), which is a common condition. Certain people are at risk for developing Type 2 diabetes. If you have risk factors, your provider will likely recommend regular screening no matter your age. The American Diabetes Association recommends regular screening for anyone age 35 or older.


Many healthcare providers, such as nurses, can perform a capillary (finger prick) blood glucose test. These tests involve a glucose meter and a test strip, which show your blood sugar result within seconds.


If your blood glucose test is part of a basic or comprehensive metabolic panel, you may also need to fast for several hours before your blood draw. In any case, your healthcare provider will let you know if you need to follow any special instructions.


If your fasting blood glucose level is 100 to 125 mg/dL (5.6 to 6.9 mmol/L), it usually means you have prediabetes. People with prediabetes have up to a 50% chance of developing Type 2 diabetes over the next five to 10 years. But you can take steps to prevent Type 2 diabetes from developing.


Healthcare providers rely on more than a single blood glucose test to diagnose diabetes or another condition. In any case, your provider will carefully interpret your results and discuss them with you.


People with diabetes check their blood glucose levels by poking their fingertips and using a blood glucose meter or a continuous glucose monitor (CGM) to measure the blood glucose level at that moment. Read on to find out how to use a blood glucose meter. To find out more about CGMs, start by talking to your doctor.


When you finish the blood glucose check, write down your results and note what factors may have affected them, such as food, activity, and stress. Take a close look at your blood glucose record to see if your level is too high or too low several days in a row at about the same time. If the same thing keeps happening, it might be time to change your diabetes care plan. Work with your doctor or diabetes educator to learn what your results mean for you. It can take time to make adjustments and get things just right. And do ask your doctor if you should report results out of a certain range right away by phone.


Keep in mind that blood glucose results often trigger strong feelings. Blood glucose numbers can leave you upset, confused, frustrated, angry, or down. It's easy to use the numbers to judge yourself. Remind yourself that tracking your blood glucose level is simply a way to know how well your diabetes care plan is working, and whether that plan may need to change.


The A1C test measures your average blood sugar level over the past 2 or 3 months. An A1C below 5.7% is normal, between 5.7 and 6.4% indicates you have prediabetes, and 6.5% or higher indicates you have diabetes.


This measures your blood sugar after an overnight fast (not eating). A fasting blood sugar level of 99 mg/dL or lower is normal, 100 to 125 mg/dL indicates you have prediabetes, and 126 mg/dL or higher indicates you have diabetes.


If your doctor thinks you have type 1 diabetes, your blood may also tested for autoantibodies (substances that indicate your body is attacking itself) that are often present in type 1 diabetes but not in type 2 diabetes. You may have your urine tested for ketones (produced when your body burns fat for energy), which also indicate type 1 diabetes instead of type 2 diabetes.


Blood sugar, or glucose, is the main sugar found in your blood. It comes from the food you eat, and is your body's main source of energy. Your blood carries glucose to all of your body's cells to use for energy.


Diabetes is a disease in which your blood sugar levels are too high. Over time, having too much glucose in your blood can cause serious problems. Even if you don't have diabetes, sometimes you may have problems with blood sugar that is too low or too high. Keeping a regular schedule of eating, activity, and taking any medicines you need can help.


If you do have diabetes, it is very important to keep your blood sugar numbers in your target range. You may need to check your blood sugar several times each day. Your health care provider will also do a blood test called an A1C. It checks your average blood sugar level over the past three months. If your blood sugar is too high, you may need to take medicines and/or follow a special diet.


Glucose is the most important carbohydrate fuel in the body. In the fed state, the majority of circulating glucose comes from the diet; in the fasting state, gluconeogenesis and glycogenolysis maintain glucose concentrations. Very little glucose is found in the diet as glucose; most is found in more complex carbohydrates that are broken down to monosaccharides though the digestive process. About half of the total carbohydrates in the diet are in the form of polysaccharides and the remainder as simpler sugars. About two-thirds of the sugar in the diet is sucrose, which is a disaccharide of glucose and fructose. Glucose is classified as a monosaccharide because it cannot be broken down further by hydrolysis. It is further classified as a hexose because of its six-carbon skeleton and as an aldose, because of the presence of an aldehyde group on carbon 1. The aldehyde group condenses with a hydroxyl group so that glucose exists as a hemiacetal ring structure. This ring structure explains many of the reactions of glucose.


Ordinarily the concentration of glucose in the blood is maintained at a relatively stable concentration from 80 to 120 mg/dl. The strong reducing properties of glucose made it relatively easy to measure and thus the clinical estimation of circulating glucose was one of the earliest tests available to the clinician. The recent introduction of microglucose oxidase technology has now made it possible for the patient to measure his or her own blood glucose concentration and undoubtedly makes the estimation of blood glucose the most widely used test of blood chemistry. An understanding of the methods of blood glucose measurement will help the clinician to interpret values and avoid the pitfalls of inaccurate testing.


The concentration of glucose is highest in the arterial circulation. Laboratory determinations are usually done on venous samples. If the venous circulation is delayed, such as by leaving a tourniquet on for a prolonged period of time, the concentration falls even further. Thus, samples should be obtained after releasing the tourniquet. Studies have shown that blood glucose concentration may fall as much as 25 mg/dl when a tourniquet has been left in place for 6 minutes. The concentration of glucose in capillary samples is intermediate between venous and arterial. Warming the extremity increases the capillary flow and "arterializes" the sample, while cooling or a tourniquet decreases the flow and lowers the concentration of glucose.


Both red cells and leukocytes contain glycolytic enzymes. Therefore glucose will be consumed and the concentration of glucose in a sample of whole blood will decline with time. The rate of loss is generally said to be approximately 5% per hour, but may be as rapid as 40% in 3 hours. Consumption of glucose in whole blood samples can be prevented by adding sodium fluoride to the specimen to inhibit the glycolytic enzymes. This approach is the generally applied method in the clinical laboratory. It is effective except in situations where the system is overwhelmed, such as in specimens from patients with leukemia, which contain large numbers of leukocytes. Sodium fluoride has a major disadvantage in that its use makes the sample unacceptable for other determinations such as sodium and uric acid.


Rapid separation of the sample or cooling will also prevent glycolysis and will allow the sample to be used for other determinations. Unhemolyzed samples that have been separated within 30 minutes of drawing are generally considered adequate. Rapid cooling of the sample followed by centrifugation is even more effective in preventing glycolysis. These methods require more attention to detail and are therefore not suitable for routine laboratory use. On occasion, circumstances will require that the glucose concentration be determined on an ordinary serum sample. If the specimen has been promptly centrifuged, it is reasonable to ask the laboratory to measure the glucose concentration even though a sodium fluoride (green top) tube was not used.


Glucose concentration may be determined in whole blood, plasma, or serum samples. If whole blood is used, the concentration will be lower than if plasma or serum is used. This is due to the greater water content of the cellular fraction. Under usual circumstances, the concentration of glucose in whole blood is about 15% lower than in plasma or serum, but the difference will be less in patients with low hematocrits.


Blood glucose cannot be determined accurately on postmortem specimens because both glycogenolysis and glycolysis continue after death. A reasonable estimate of the antemortem blood glucose concentration can be obtained by measuring the glucose concentration of the vitreous of the eye, which does not contain glycolytic enzymes.


Glucose oxidase and reagents to measure the generation of hydrogen peroxide can be bonded to filter paper and the system used to measure glucose concentrations in a drop of capillary blood. This has resulted in the most important change in diabetes management since the introduction of insulin.


Patients are instructed to obtain a blood sample by pricking their fingertip with a lancet. Spring-loaded lancets are available. They are easy to use and cause minimal discomfort. Surprisingly, many patients consider the discomfort of the finger stick preferable to the inconvenience and aesthetic unpleasantness of obtaining a urine sample for testing. A drop of whole capillary blood is then placed on the reagent bonded to the paper strip. Instead of using a known volume of blood, an excess of blood is exposed to a fixed quantity of glucose oxidase for a finite period of time to estimate concentration. After the specified time, usually 1 minute, the excess blood is removed by washing or wiping and the color is allowed to develop. The concentration is then estimated by comparing to a color chart, or by using a portable reflectance meter specific to the reagent strip, to measure the developed color. Reflectance meters for measuring blood glucose are becoming increasingly sophisticated, compact, and reliable. Shirt-pocket-size models are now available, and prototype models that store the time, date, result, and insulin doses for later graphic printing at the patient's home or physician's office have been developed. Undoubtedly, reflectance meters that have access to complex algorithms for recommending changes in insulin dose individualized to a specific patient will be possible in the near future. 041b061a72


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