Blood Glucose Test
By
Vian A. Ahmed
Contents:
• What is a blood glucose test?
• What Is Diabetes Mellitus & its types?
• Types of blood glucose tests
• Indications of blood glucose testing
• Errors in blood glucose testing
What is a blood glucose test?
• It is a fundamental diagnostic tool used in medicine to assess the
concentration of glucose (sugar) in a patient's blood.
• Hyperglycemia means high blood glucose. It occurs when the body does
not produce enough insulin or does not respond to insulin correctly. In
both cases, glucose stays in the blood instead of being sent to the cells
• hypoglycemia means Low blood sugar, usually affects people
with diabetes who take insulin or some other diabetes medicines. It's rare
in people without diabetes.
What Is Diabetes Mellitus?
• Diabetes is a chronic disease that occurs either when the pancreas does
not produce enough insulin or when the body cannot effectively use the
insulin it produces.
The three main types of diabetes are:
Type 1 Diabetes is an autoimmune condition. It happens when your body can’t make insulin
because your immune system destroys the cells that make insulin.
Type 2 Diabetes It happens when your body doesn’t make enough insulin or your body doesn’t
use the insulin it makes properly.
Gestational Diabetes is high blood sugar (glucose) that develops during pregnancy and usually
disappears after giving birth, it is more common in the second or third trimester.
Other specific types
a) Monogenic diabetes mellitus: maturity-onset diabetes of the young (MODY)
b) Genetic defects of insulin action (e.g., lipodystrophies)
c) Pancreatic disease (e.g. pancreatitis, pancreatectomy, neoplastic disease)
d) Excess endogenous production of hormonal antagonists to insulin, (e.g. Growth
hormone, Glucocorticoids, Glucagon, Thyroid hormones)
e) Drug-induced (e.g. glucocorticoids, HIV drugs)
Prediabetes is a condition where blood glucose levels are elevated but not high enough for a
diabetes diagnosis. Early intervention can prevent the progression to diabetes.
Prediabetes can be defined in terms of either impaired glucose tolerance (IGT), impaired
fasting glucose (IFG) or HbA1c. The diagnostic criteria differ between WHO, NICE and the
American Diabetes Association (ADA).
Table 1. Prediabetes diagnostic criteria according to health authorities.
Diagnostic criterion WHO ADA NICE
HbA1c Not recommended 39–47 mmol/mol 42–47 mmol/mol
for diagnosis (5.7–6.4%) (6.0–6.4%)
2-hour OGTT 140-198mg/dl 140-198mg/dl 140-198mg/dl
Fasting plasma glucose 110-124mg/dl 100-124mg/dl 110-124mg/dl
ADA=American Diabetes Association;
NICE=National Institute for Health and Care Excellence;
OGTT=oral glucose tolerance test;
WHO=World Health Organization.
Types of blood glucose tests
1. Fasting Blood Sugar Test (FBS): It is typically conducted in the morning
after an overnight fast.
2. Postprandial Blood Glucose Test: This test measures blood glucose levels
two hours after eating a meal.
3. Hemoglobin A1c Test: The HbA1c test measures the average blood sugar
levels over the past 2-3 months, It measures the percentage of
hemoglobin that is coated with glucose over the past two to three
months.
4. Random Blood Sugar Test: It can be conducted at any time of the day.
5. Oral Glucose Tolerance Test (OGTT):It is a medical test used to assess
how well your body processes glucose, after you consume a standardized
glucose solution.
Types of blood glucose tests
Oral Glucose Tolerance Test (OGTT):
An OGTT is performed when the patient’s fasting glucose is equivocal
(110-124mg/dl), or during pregnancy to test for gestational diabetes.
• After the fasting blood sample is obtained, the patient are asked to
drink a standardized glucose solution that contains a specific amount of
glucose (usually 75 grams).
• Blood samples are taken at specific time intervals, typically 1 and 2
hours after consuming the glucose solution. These samples help assess
how your body processes glucose and how quickly your blood sugar
levels rise and fall.
Continuous Glucose Monitoring (CGM):
A small sensor is placed under the skin, usually on the abdomen, to
continuously measure glucose levels in the interstitial fluid. The sensor
transmits data to a monitor or a smartphone.
Different to traditional blood glucose measurement systems, systems for continuous glucose
monitoring (CGM) measure glucose in interstitial fluid (ISF). The assumption is that glucose levels in
blood and ISF are practically the same and that the information provided can be used
interchangeably.
Fasting Blood Glucose Tolerance Random Blood
Result* A1C Test Sugar Test Test Sugar Test
Diabetes 6.5% or above 126 mg/dL or above 200 mg/dL or above 200 mg/dL or above
Prediabetes 5.7 – 6.4% 100 – 125 mg/dL 140 – 199 mg/dL N/A
Normal Below 5.7% 99 mg/dL or below 140 mg/dL or below N/A
In asymptomatic patients, two diagnostic tests are required to confirm diabetes
Indications for blood glucose test
1. Diagnosis of Diabetes
2. Monitoring Diabetes Management
3. Gestational Diabetes Screening
4. Screening for Prediabetes
5. Assessment of Hypoglycemia
6. Monitoring Response to Treatment
7. Routine Health Check-ups
8. As a Vital singe : Vital signs (temperature, pulse rate, blood pressure, and respiratory rate)
are clinical measurements that indicate the essential physiological functions necessary for life.
The most common types of specimens used for glucose
determination are:
• Blood (Serum or Plasma)
• Whole Blood
• Urine
• Cerebrospinal Fluid (CSF)
• Interstitial Fluid
Blood glucose test
Principle:
Glucose is oxidized by GOD to gluconic acid and hydrogen peroxide which in
conjunction with POD, reacts with chloro-4-phenol and PAP to form a red
quinoneimine. The absorbance of the colored complex, proportional to the
concentration of glucose in the specimen is measured at 500 nm.
GOD
• β-D-Glucose + H2O + O2 D-Gluconate + H2O2
H2O2
• 4-AA + Phenol Quinoneimin + H2O
POD Red complex
• GOD= glucose oxidase
• POD= peroxidase
• 4-AA = 4-aminoantipyrine
Errors in blood glucose testing can occur
1. Hemolyzed sample: the glucose in the sample is being metabolized by the released
enzymes, causing an artificial decrease in the measured glucose concentration.
2. Medication Interference: High doses of vitamin C, either through supplements or
vitamin C-rich foods, can interfere with glucose oxidase-based glucose meters, leading to
falsely elevated blood glucose readings
3. Dehydration or Overhydration
4. Inadequate Fasting
5. Inaccurate Calibration of Instruments
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