Blood Sugar Testing: why, when and how?
A blood glucose test is used to determine the level of sugar (glucose) in the blood. Glucose is the result of the breakdown of carbohydrates. The presence of glucose in the bloodstream stimulates the release of insulin which is a hormone produce by the pancreas. Insulin is necessary to assist the body’s cells to absorb the glucose, from which comes most of the body’s energy.
Blood glucose levels go up a little whenever you take in food. When glucose levels go up, the pancreas is stimulated to produce insulin to move the glucose into the cells so that blood glucose levels will not be excessively high. If blood glucose stays high for too long a time, it can bring problems to your body.
There are many kinds of blood glucose tests.
- Glycohemoglobin A1c:
This measures the amount of glucose attached to the hemoglobin in red blood cells. It can diagnose diabetes and it can indicate the level of management of diabetes for three consecutive months before the test. With this knowledge, it shows whether there is a need for a change in diabetes medications. A1c test results give an estimate of your blood glucose level average which is also referred to as estimated average glucose(eAG).
- OGTT (Oral Glucose Tolerance Test):
It is used for diagnosing diabetes and prediabetes. It is a number of tests made after the patient has taken a glucose solution. It is usually used for diagnosing gestational diabetes which can occur during a pregnancy. Usually this test is not applied to diagnose diabetes in non-pregnant patients.
- RBS (Random Blood Sugar):
This test determines the amount of blood glucose at any time without taking into consideration your meals. Throughout a day, blood glucose is measured and if the patient is healthy his sugar levels do not differ much. So, when blood sugar levels are found to vary a lot, it implies that there is a problem. It is also not used for diagnosing diabetes. Another name for this test is casual blood glucose test.
- 2-hour Postprandial Blood Sugar:
This is a test used two hours from the beginning of a meal to determine the amount of blood sugar. It is not for diagnosing diabetes.
- FBS (Fasting Blood Sugar):
This test determines the amount of blood glucose after a fast of eight hours. Usually, this test is the first used to do a search for diabetes and prediabetes.
For a type ll diabetes diagnosis, you medical practitioner will refer to the criteria given by the ADA (American Diabetes Association).
How to Use an Insulin Pen – Mayo Clinic Patient Education – Video Guide
Why it’s done
The purpose of having a blood glucose test is to:
- Confirm extremely hypoglycemia (low blood sugar) level. To know the cause of the hypoglycemia, a test to determine insulin level and C-peptide in the blood is carried out at the same time as the blood glucose test.
- Look out for diabetes that happens during a pregnancy.
- Consistent check on diabetes treatment.
- Examine for diabetes.
A fasting blood glucose test is used to confirm prediabetes. According to the ADA (American Diabetes Association), prediabetes is confirmed with glucose levels at 5.6 - 6.9 mmol/L(110 - 125 mg/dl).
Preparing for the Test
- Glycohemoglobin A1c and Oral Glucose Tolerance Test:
- RBS (Random Blood Sugar):
There is no need to be prepared for this test.
- 2-hour Postprandial Blood Sugar:
For the purpose of this test, begin eating two hours before blood is drawn for the test. The usual way to have this test is a blood glucose test done at home.
- FBS (Fasting Blood Sugar):
As the name of the test implies, there must be a total fast before the test for a minimum period of 8 hours except for the drinking of plain water.
So, If you have diabetes, you are required to delay your morning medications until the test has been carried out.
Discuss with your medical practitioner if you have any queries on the necessity of having the test, undesirable effects, how it is carried out and the implications of the results. Filling up a medical test information form can assist you to know the need for the test.
How it’s done
The medical practitioner taking the blood sample will:
- Put an stretchable band around the area of your arm between the elbow and the shoulder to prevent blood flow. This will cause the veins to enlarge so that it is easy to push a needle into the enlarged vein.
- Make sure the needle site will be clean by using alcohol to wipe it.
- Inject the vein with the needle, perhaps with more than a needle.
- Connect the tube and needle so that blood can flow into the tube and fill it.
- When sufficient blood has been collected, detach the band.
- Place a piece of cotton over the spot where the needle is taken out.
- Put some pressure on the cotton at the site before bandaging it.
How It Feels
The band put around your upper arm may be uncomfortably tight. When it comes to the going into the vein, some may feel no discomfort or pain while others may experience the feeling of being stung or pinched.
There is hardly any risk involved when it is merely the drawing of blood from a vein. However, you may get a darker spot on the skin indicating that skin has been punctured. This can be lessened by applying pressure on the needle site for a few minutes. You can also get, but seldom, a little inflammation called phlebitis at the needle site. You can apply a warm piece of cloth over the inflammation a number of times every day to treat it. For people who have bleeding problems, non-stop bleeding can occur. If blood-thinning medicines such as aspirin and warfarin have been used, such non-stop bleeding can happen. So, you must inform your medical practitioner about these medicines before the test.
Blood Glucose Test Results
When a blood sugar test is used to determine the amount of glucose in your blood, the results usually takes an hour or two to be ready. Glucose levels in a venous blood sample are different from glucose levels in the drop of blood taken from your finger.
The given normal values known as a reference range are merely information given to assist since the ranges differ from one lab to another. Besides, may show a range that is different from that which is normal in the guidelines. However, your results ought to come together with the range used by your lab. Then, your medical practitioner will judge the results with consideration given on your health as well as other connected factors. It implies that even if you get a value beyond what is given as normal, your doctor may consider it normal for you. Below are normal values given for the various tests.
- Glycohemoglobin A1c or Oral Glucose Tolerance Test:
- Random (casual):
Levels will differ as it depends upon the time and the amount of food in the meal before the test. Normally: 4.4-6.6 mmol/L (80-120 mg/dL) before consumption of food or upon waking up; 5.5-7.7 mmol/L (100-140 mg/dL) just before sleep.
- 2 hours after eating (Postprandial):
Lower than 7.8 mmol/L (140 mg/dL) for people younger than 51 years of age; lower than 8.3 mmol/L (150 mg/dL) for people between the ages 50-60; lower than 8.9 mmol/L (160 mg/dL) for people more than 60 years old.
- Fasting blood glucose:
It should be equivalent to, if not less than, 6.1 mmol/L (110 mg/dL).
There are a number of health problems which can influence your blood sugar levels. In this, your medical practitioner will have to evaluate unexplained results through further knowledge of symptoms experienced and previous health problems.
Signs of hypoglycemia together with a fasting sugar level lower than 2.2 mmol/L (40 mg/dL) in women or lower than 2.8 mmol/L (50 mg/dL) in men can be an indication of insulinoma which is an abnormal growth which gives out produces exceptionally high quantities of insulin.
Low glucose levels can also be due to:
- Diabetes medicines.
- Malnutrition or anorexia which is an eating problem.
- Kidney failure.
- Liver disease; cirrhosis for example.
- A mass of diseased cells called a tumor in the pituitary gland.
- Addison’s disease.
To find out if you have type 2 diabetes, your medical practitioner can apply the criteria issued by the ADA (American Diabetes Association).
There are other health problems that can result in raised blood sugar levels. Listed below are such health problems.
- Over production of growth hormone known as acromegaly.
- Certain medications.
- Cushing’s syndrome.
- Heart attack.
- Great stress.
What affects the blood glucose test?
There are things which can invalidate a test. Below are certain factors which can affect tests.
- Not having an 8 hour fast before a fasting blood test or eating or drinking 2 hours before a 2-hour postprandial test.
- Taking alcohol.
- Sickness, stress, smoking as well as caffeine.
- Medicine for birth control, hypertension, corticosteroids (prednisone), propranolol (Inderal), niacin, hydrochlorothiazide (Oretic , Esidrix), triamterene (Dyazide, Dyrenium), furosemide (Lasix) or phenytoin (Dilantin). There are medicines which can alter the blood glucose test results. So tell your medical practitioner everything about the medicines you are taking.