Plasma Glucose Concentration Tests

Fasting Plasma Glucose (FPG):

Glucose measurement can be done in the whole blood or plasma. Whole blood is composed of a liquid part plus blood cells. The liquid part of blood is called as plasma, which is milky white in color. When glucose level is measured in plasma it is called as Plasma glucose level and its unit of measurement is milligrams/ deciliters (mg/dL). Plasma glucose level can be measured at various times in a day.

  • Normal FPG is < 100 mg/dL.
  • When FPG is between 100 to 125 mg/dL it is called as Prediabetes or Impaired Fasting Glucose.
  • FPG ≥ 126 mg/dL indicates individual is diabetic

Some times FPG does not indicate clear cut increase in blood glucose level. In this situation repeat testing on a different day is required. Your doctor will take the decision depending upon symptoms, clinical examination and other relevant finding. Always discuss laboratory reports with your doctor.

American Diabetic Association recommends that FPG should be maintained between 70 to 130 mg/dL in patients of diabetes. Therefore your doctor may advise repeated checking of FPG from time to time to keep watch on your glucose level. Ask your doctor about right FPG target for you

Postprandial Plasma Glucose (PPG):

Here the word Post Prandial means 2 hours from the beginning of meals. So if your plasma glucose is measured two hours after the meals it is called as Postprandial Plasma Glucose. Normal PPG is < 140 mg/dL.

American Diabetic Association recommends that PPG should be maintained less than 180 mg/dL in patients of diabetes. Ask your doctor about right PPG target for you.

Random Plasma Glucose:

When plasma glucose is measured any time of day without regards to time since last food it is called as Random Plasma Glucose. When Random Plasma Glucose is more than 200 mg/dL along with the classical symptoms of increased blood glucose level like increased frequency of urination, excessive hunger and weight loss it indicates that individual is diabetic. Discuss the laboratory report with your doctor as reports are always interpreted in the light of clinical findings of the doctor.

Oral Glucose Tolerance Test (OGTT):

ADA recommends OGTT in the patients with prediabetes i.e. FPG between 100 to 125 mg/dL to know more details.

For oral glucose tolerance test, you must fast overnight (at least 8 but not more than 16 hours) and go to the laboratory in the morning. First, your fasting plasma glucose is tested. After this test, you receive 75 grams of glucose. The oral glucose tolerance test measures blood glucose levels five times over a period of 3 hours (Fasting i.e. before ingesting glucose solution, 30 min, 60 min, 120 min and 180 minutes after the ingestion of glucose solution.)

For the test to give reliable results, you must be in good health (not have any other illnesses, not even a cold). Also, you should be normally active (for example, not lying down as an inpatient in a hospital) and taking no medicines that could affect your blood glucose. For 3 days before the test, you should have eaten a diet high in carbohydrates (150-200 grams per day). The morning of the test, you should not smoke or drink coffee.