For those who suffer from diabetes or who may be at risk, the blood sugar test is the gold standard of measurement. However, more than one type of test is usually used, depending on the status of the patient. The tests all measure the body's ability to process glucose. Here is an overview of the four types of blood sugar tests, with information on the average or normal readings for each. There are two units of measurement for the first three tests presented. The first is expressed as milligrams of glucose per deciliter of blood, abbreviated to mg/dL. The alternate value is millimoles per liter, or mmol/L. Normal values for each test will be given in both ways, with millimoles per liter shown in parentheses. For the final type of test (glycated hemoglobin test), the critical value is a percentage.
Random
The random blood sugar test, unlike other tests that must be given at specific times in relation to eating or drinking, may be administered at any time. A blood sugar level higher than 140 mg/dL (7.8 mmol/L) may indicate a prediabetic condition. If the reading goes above 200 mg/dL (11.1 mmol/L), the Mayo Clinic reports, Type 1 or Type 2 diabetes is suspected and additional tests may be needed.
Fasting
The fasting blood sugar test requires that the patient not have eaten or drunk anything except water for a minimum of eight hours. The normal values for a fasting blood sugar test are 70 to 100 mg/dL (3.9 to 5.6 mmol/L). Higher readings up to 125 mg/dL (6.9 mmol/L) preliminarily indicate a prediabetic condition. Readings above 125 mg/dL (6.9 mmol/L) suggest type 1 or type 2 diabetes, according to the Mayo Clinic, and need to be followed up with further testing.
Oral Glucose Tolerance
The oral glucose tolerance test is performed following hours of fasting, the drinking of a sugar solution, and another hour's wait. A blood test is performed and is then repeated after another one or two hours. The Mayo Clinic reports that normal values are below 140 mg/dL (7.8 mmol/L). Readings of 140 to 199 mg/dL (7.8 to 11.0 mmol/L) may indicate a prediabetic condition, and blood sugar levels above 200 mg/dL (11.1 mmol/L) indicate that the patient may be diabetic.
A1C
The glycated hemoglobin test, alternatively called the A1C test, is a measurement of average blood sugar level over a period of two to three months. The key value is the percentage of hemoglobin in red blood cells that is coated in sugar. The percentage considered normal is approximately 4 to 6 percent. The patient may have prediabetes when the A1C level is between 6 and 6.5 percent, according to the Mayo Clinic, while 6.5 percent or higher (especially 7 percent or above) is suggestive of diabetes, particularly in tests administered at separate times. The A1C test is useful both for diagnosing diabetes and also measuring how well a patient is managing diabetes.
Variations of "Normal"
Many factors can skew the results of any of these blood sugar tests so that a seemingly abnormal reading need not be considered as such, according to a report by Amarillo Medical Specialists (AMS) in Texas. These factors include sex, age, racial heritage, general state of health and physical condition, prescription or non-prescription drugs being taken, and whether the patient drinks alcohol, according to AMS. The menstrual cycle of pre-menopausal women is a factor, as is the integrity of the lab procedures. Also, if two different labs use the same procedure, their results are not necessarily comparable.
Reading of Tests
AMS cautions that only a physician armed with knowledge of the specific patient's characteristics can be considered qualified to evaluate the results of blood sugar tests. This is especially true when considering variations in similar tests performed at different times.
