Blood Glucose
➔ Glucose is the source of energy for cells and is transported into cells by
insulin. As blood glucose levels rise following ingestion of food, the
pancreas releases insulin to move the glucose from blood into cells.
➔ There are four blood glucose tests:
◆ Oral glucose tolerance test (OGTT): This test measures the
blood glucose levels at specific time intervals after the patient
ingests a glucose drink. The OGTT is ordered to screen for
gestational diabetes and to confirm positive results of other blood
glucose tests.
◆ Two-hour postprandial blood sugar test: This test measures
blood glucose levels 2 hours after the patient ingests food.
◆ Fasting blood glucose (FBG) test: This test measures blood
glucose levels after the patient has fasted for 8 hours. The FBG test
is the initial test for diabetes.
◆ Random blood glucose (RBG): This test measures blood glucose
levels several times a day regardless of food intake.
➔ Hint
◆ Glucose levels can also be measured in urine; however, this is not
used to diagnose or monitor glucose levels. The healthcare
provider may order the glycohemoglobin (GHb) blood test, which is
used to monitor blood glucose levels for the previous 120 days.
◆ The blood glucose test for diagnosing diabetes must be repeated
on two different days.
➔ WHAT IS BEING MEASURED?
◆ FBG test requires the patient to fast for 8 hours before the test is
administered. Insulin and other diabetes medication are withheld
until the test is administered.
◆ Two-hour postprandial test requires the patient to eat a normal
meal 2 hours before the test is administered.
◆ Oral glucose tolerance test requires the patient to fast 8 hours
before the test. Ingesting water is permitted. A blood sample is
taken to be used as a baseline. The patient ingests a glucose drink.
A blood sample is taken in hourly intervals for 3 hours
➔ RATIONALE FOR THE TEST
◆ Screen for
● Diabetes
● Hypoglycemia
➔ Assessment of the treatment for diabetes.
➔ NURSING IMPLICATIONS
◆ Assess if the patient
● Is ill. Illness can increase blood glucose levels and affect the
test result.
● Smokes, since this can affect the test result.
● Uses caffeine, since this can affect the test result.
● Is experiencing stress, since this can affect the test result.
● Has eaten or fasted according to procedures for the blood
glucose test.
● Has taken Dyrenium, Dyazide, Dilantin, Lasix, niacin,
Inderal, Esidrix, Hydro Par, Oretic, prednisone, or birth
control pills, since these medications may affect the test
result.
➔ Normal Range
◆ FBG test: 70 to 99 mg/dL
◆ Two-hour postprandial blood sugar test: 70 to 145 mg/dL
◆ RBG test: 70 to 125 mg/dL
➔ Understanding the Result
◆ High blood glucose may indicate
● Diabetes
○ FBG test: Greater than 125 mg/dL
○ Two-hour postprandial blood sugar test: Greater
than 199 mg/dL
○ RBG test: Greater than 199 mg/dL and the presence
of symptoms of diabetes
● Prediabetes
○ FBG test: 100 to 125 mg/dL
● Acromegaly
● Cushing syndrome
● Stroke
● Myocardial infarction
● That the patient has taken corticosteroid medication
◆ Low blood glucose may indicate
● Hypoglycemia (FBG less than 40 mg/dL)
● Insulinoma/insulin-producing tumor
● Hypothyroidism
● Addison disease
● Kidney failure
● Malnutrition
● Cirrhosis
● Anorexia
● That the patient has taken insulin or other diabetes
medication
➔ TEACH THE PATIENT
◆ Explain
● Why the blood sample is taken.
● The dietary restriction required by the test if any.
● That the healthcare provider may ask the patient to stop
taking Dyrenium, Dyazide, Dilantin, Lasix, niacin, Inderal,
Esidrix, Hydro Par, Oretic, prednisone, or birth control pills
for 2 weeks prior to the test.
