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Different Laboratory Tests to Diagnose Diabetes

Updated on July 27, 2014

Blood Glucose Test

Laboratory tests for diagnosing diabetes
Laboratory tests for diagnosing diabetes | Source

Diabetes Mellitus is a condition or a disease when there is an uncontrolled blood sugar level (hyperglycemia) due to defect in insulin production, the body's resistance to insulin, or both. Different laboratory tests, specifically the blood glucose tests, are used to diagnose Diabetes. There are certain criteria a person must be met to be able to be considered diabetic or only under prediabetic states.

Types of Diabetes

The Basic's of Diabetes


The different categories of diabetes are divided into four:

  • Type 1 Diabetes
  • Type 2 Diabetes
  • Gestational Diabetes
  • Other Specific Types of Diabetes


For Diabetes, the three classical symptoms are apparent in varying degrees.

For Type 1 DM, the signs and symptoms are highly observable. This type of diabetes is usually developed during adolescent years and is accredited to other diseases or infections (or other environmental factors) acquired that trigger the production of auto-antibodies toward the destruction of very own pancreatic cells.

Consequently, the glucose remains in the bloodstream. Since secretion of insulin becomes deficient producing lower energy metabolism due to cell's non-absorption of glucose, this will trigger the brain to eat more (polyphagia) to compensate for lower glucose level inside the cells to produce energy. As a result, hyperglycemia will stimulate the brain to drink more (polydipsia) to excrete the excess sugar in the body which will result to frequent urination (polyuria) and (or) vice versa.

Other Types of Diabetes

Other types of diabetes are said to be due to:

  • genetic defects
  • other pancreatic diseases
  • beta cells destruction due to medication or chemical intake
  • hormonal imbalance resulting from another medical condition
  • or rare autoimmune diseases

These may show signs and symptoms of Type 1 and Type 2 Diabetes. Proper diagnosis is also with the help of laboratory tests.

Other symptoms include weight loss, kidney diseases, nerve and blood vessel damages. With the occurrence of symptoms, the person will enable to seek medical attention. Laboratory testing is requested for proper diagnosis.

For Type 2 Diabetes which is appointed to body's insulin resistance or the cells inability to uptake glucose because of insulin-cell-binding discrepancy, the signs and symptoms are not apparent and the development is experienced over time.

Together with Gestational Diabetes or the development of hyperglycemia during pregnancy, laboratory testing is usually required for initial detection and diagnosis.

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Laboratory Tests for Diagnosing Diabetes

There are various blood glucose tests for diagnosing diabetes. Aside from the manifestation of diabetic symptoms, if one of these tests reached the diabetic value of that particular test, another (different blood glucose exam) test must be performed on the succeeding day for confirmatory reason. Proper diagnosis of diabetes is determined if the two results coincide with each other.

(Note: Glucose values are adapted from American Diabetes Association)


Fasting Plasma Glucose (values adapted from ADA)
Fasting Plasma Glucose (values adapted from ADA) | Source

Fasting Plasma Glucose (FPG) or Fasting Blood Sugar (FBS)

FBS or FPG is a blood glucose test done in a patient under 8 hours of fasting. Fasting means no food or drink intake within the specified time. Extraction of blood is done once under the condition indicated. Over fasting will result to falsely low glucose level.

Prediabetes (which is also called Impaired Fasting Glucose) is not yet under the category of diabetes and the person is not considered diabetic but only has a high risk of developing diabetes later in life. The FPG result of greater than 126 mg/dl is a diagnosis of diabetes.

OGTT (2-Hour Post Glucose Load)

A. 2 hours post glucose load B. Values adapted from American Diabetes Association
A. 2 hours post glucose load B. Values adapted from American Diabetes Association | Source

Prediabetes is also called Impaired Glucose Tolerance if using an OGTT test; on the other hand, if using the FBS test, prediabetes is referred to as Impaired Fasting Glucose.

Oral Glucose Tolerance Test

OGTT is a blood test used to determine how our body can tolerate the specific amount of glucose taken. Though it is not recommended as a routine use due to inconvenience brought to patients with the procedure, it is more reliable in confirming and diagnosing diabetes than FBS.

The Procedure

The procedure requires the patient to undergo fasting and is advised to be performed in the morning. Carbohydrate consumption of 150-200 grams is advised to the patient for three consecutive days before the test's day.

Usually a person is given an oral sugar solution (75 grams of glucose). Blood extraction is done before and 2 hours after the oral glucose intake. Patients with the OGTT result of greater than or equal to 200 mg/dl is considered diabetic.

3-Hour OGTT

A. 3-hour OGTT using 100 grams of glucose B. Values adapted from National Diabetes Information Clearinghouse
A. 3-hour OGTT using 100 grams of glucose B. Values adapted from National Diabetes Information Clearinghouse | Source

3-Hour Oral Glucose Tolerance Test

For detection and evaluation of Gestational Diabetes, a 3-hour OGTT is considered more reliable and confirmatory (though the procedure is more uncomfortable because of the required four blood extractions and 8 hours of fasting to complete the test).

The Procedure

The first blood extraction is for fasting blood sugar. After, the pregnant is asked to drink 100 grams of glucose load (or as requested by the doctor).Specific time must be noted and observed after she emptied the bottle or drank the whole solution. Three successive blood extractions with one hour apart from the time the patient finished drinking must be completed. The patient must not eat or drink, smoke, and exercise before and during this time or wait until the 4th blood extraction has been performed).

A1C/Glycosylated Hemoglobin/ Hemoglobin A1C

The A1C is a blood test used to detect the average blood sugar level for the past two to three months. It is more convenient, does not need fasting, and single blood drawn can be performed any time of a day.

A1C helps the medical practitioner to see how the body works well and consume glucose for the past few months. But then, in some circumstances, interpretation of A1C must be taken with caution if the patient has anemia (especially sickle cell anemia), chronic kidney diseases, or liver diseases.

Glycosylated Hemoglobin

A. HbA1C or A1C B. Values are adapted from American Diabetes Association
A. HbA1C or A1C B. Values are adapted from American Diabetes Association | Source

The red blood cells stay in the blood stream for 120 days (3 months) before they were replaced by the new production of red cells in the bone marrow. Glucose enters the red blood cells and links or glycates to the hemoglobin, parts of blood that carry oxygen to different body cells.

Increase in blood glucose will also increase the binding of glucose to hemoglobin which will yield higher result of A1C. The result of greater than or equal to 6.5% is a diagnostic criterion for diabetes.

Random or Casual Plasma Glucose

A. RBS/RPG/CPG B. Values are adapted from American Diabetes Association
A. RBS/RPG/CPG B. Values are adapted from American Diabetes Association | Source

Random Blood Sugar (RBS) or Random Plasma Glucose (RPG)Test

RPG is a glucose blood test performed any time of the day in the non fasting state. A person with RBS result of 200mg/dl or higher is said to be a diabetic.

Urine Dipstick Test for Sugar and Ketone

Urine glucose

 Test's results for urine glucose
Test's results for urine glucose | Source

Urine Sugar

Urine sugar is not considered a diagnostic test for diabetes, but it can serve as an aid in detecting hyperglycemia. Excess glucose is usually excreted in the urine when it reached and passed the maximum urine glucose threshold of 180 mg/dl.

Urine glucose (and ketones) are easily detected in the urine using urine dipstick test. Clean-midstream catch urine must be provided by the patient.

The pad is coated with chemicals that changes color when it reacts to the detected glucose (or ketones) in the urine. The color changes compare to the color chart (in case of ketones,with a predetermined and quantitative ketone value) in relation to the differences in color are evaluated after the specified time indicated in the procedure.

Urine Ketone

A. Increased urine ketone results from excessive breakdown of fats B. Values are adapted from Medline Plus
A. Increased urine ketone results from excessive breakdown of fats B. Values are adapted from Medline Plus | Source

Urine Ketone Test

Ketones are made up from fats and fatty acids breakdown to produce energy. Carbohydrate is the main source of energy, but when it becomes depleted in the blood (in instances like over fasting, starvation, vomiting, and in type 1 Diabetes Mellitus) fatty acids are metabolized to compensate for the lower energy detected by the body.

To counterbalance the increased ketone in the blood (ketonemia ), the kidney will excrete excess ketones in the urine (ketonuria).

The Urine ketone test is also done when blood glucose level exceeds 240 mg/dl, if the person is having pneumonia, stroke, heart attack, nausea, or is pregnant.

Seeing things differently
Seeing things differently | Source

See the Difference

Blood glucose testing and monitoring sometimes brought bothersome or inconvenience in part of the patient. Though it adds up tiresome to the existing condition, especially if the person is already ill, the beneficial consequences of the laboratory tests are utmost important.


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