Diabetes Diagnosis: Hospital Testing Procedures Explained

Hospitals use blood tests to check for diabetes. These tests can be arranged through a GP, and the results are usually available in a few days. There are several types of blood tests used to detect diabetes, including the A1C test, the fasting plasma glucose (FPG) test, and the oral glucose tolerance test (OGTT). The A1C test measures the average blood glucose level over the past two to three months, while the FPG test measures blood glucose at a single point in time, typically after an overnight fast. The OGTT involves drinking a liquid containing glucose and measuring blood sugar levels before and after. These tests help doctors detect type 1, type 2, prediabetes, and gestational diabetes.

Blood tests

There are several types of blood tests that can be used to diagnose diabetes. One of the most common is the A1C test, which measures an individual's average blood glucose level over the past two to three months. This test does not require the patient to fast or drink anything, and diabetes is typically diagnosed at an A1C level of 6.5% or higher.

Another type of blood test is the fasting blood glucose test, which measures an individual's blood glucose level after an overnight fast (usually at least eight hours). This test is typically done first thing in the morning, before breakfast, and diabetes is diagnosed at a blood glucose level of 126 mg/dL or higher.

The oral glucose tolerance test (OGTT) is another commonly used blood test for diabetes. This test involves measuring an individual's blood glucose level before and two hours after consuming a sweet drink that contains a standard amount of glucose. Diabetes is typically diagnosed on this test at a two-hour blood glucose level of 200 mg/dL or higher. The OGTT is particularly useful for detecting prediabetes and gestational diabetes.

It is important to note that blood testing equipment available over the counter, such as a blood glucose meter, cannot be used to diagnose diabetes. If an individual suspects they may have diabetes, they should consult a healthcare professional for proper testing.

Fasting plasma glucose (FPG) test

The Fasting Plasma Glucose (FPG) test, also known as the fasting blood glucose test (FBG) or fasting blood sugar test, is a blood test that measures blood glucose levels in the body. It is a relatively simple, accurate, and inexpensive test that can screen for diabetes, prediabetes, and problems with insulin functioning. The FPG test is recommended as a screening test for people 35 or older, to be repeated every three years. It may also be used for people who have symptoms of diabetes or multiple risk factors for diabetes.

The FPG test is typically performed in the morning, after a fasting period of at least eight hours, during which only water can be consumed. This is because ingesting food or drink can raise blood sugar levels, which may impact the interpretation of the results. Fasting for several hours triggers the release of glucagon, a hormone produced by the pancreas that causes the liver to release glucose into the bloodstream.

If you do not have diabetes, your body will react to the increased blood sugar levels by producing insulin, which prevents hyperglycemia. However, if your body cannot generate enough insulin or respond appropriately to insulin, your fasting blood sugar levels will remain high, indicating potential diabetes or prediabetes.

The FPG test can be performed alone or in conjunction with other tests, such as the oral glucose tolerance test (OGTT) or the hemoglobin A1C test. While the FPG test is considered accurate and sensitive, it cannot confirm a diagnosis on its own. Therefore, if the initial FPG test results are borderline or indicate diabetes, the test will need to be repeated on a different day to confirm the results.

Oral glucose tolerance test (OGTT)

The Oral Glucose Tolerance Test (OGTT) is a common test used to detect type 2 diabetes, prediabetes, and gestational diabetes. It is a more expensive test than the FPG test and the glucose challenge test, and it is not as easy to administer.

Before the test, the patient must fast for at least 8 hours. A healthcare professional will then take a blood sample to measure the patient's fasting glucose level. The patient then drinks a liquid that is high in sugar—usually 75 grams of glucose dissolved in 250 to 300ml of water. Another blood sample is taken 2 hours later to check the patient's blood glucose level again. If the patient is pregnant, their blood will be drawn every hour for 2 to 3 hours. If the blood glucose levels are high two or more times during the OGTT, the patient may have gestational diabetes.

The OGTT is used to screen for or diagnose diabetes in people with a fasting blood glucose level that is high, but not high enough to meet the diagnosis for diabetes. A blood glucose level of over 126 mg/dL or 7 mmol/L is indicative of diabetes. A 2-hour value of 140 to 199 mg/dL (7.8 and 11.1 mmol/L) is called impaired glucose tolerance and may mean the patient has prediabetes or diabetes.

The OGTT is a simple test, and results are usually available quickly. It is important to get tested for diabetes if you have any risk factors, as prediabetes and type 2 diabetes often do not have any symptoms.

A1C test

The A1C test is a blood test that provides information about your average blood glucose (blood sugar) levels over the past 2 to 3 months. It is used to diagnose type 2 diabetes and prediabetes, and it is the primary test used for diabetes management.

The A1C test measures the amount of hemoglobin with attached glucose. Hemoglobin is the part of a red blood cell that carries oxygen to the cells. Glucose attaches to or binds with hemoglobin in the blood cells, and the higher the glucose level, the more glucose will attach to the hemoglobin. The A1C test result is reported as a percentage—the higher the percentage, the higher your blood glucose levels have been. A normal A1C level is below 5.7%, indicating that you do not have diabetes.

There are two ways to perform the A1C test. The most common method involves a phlebotomist taking a blood sample from a vein and sending it to a lab for analysis. Alternatively, a provider can obtain a blood sample through a finger prick, with results available within minutes. However, this method is only for assessing diabetes management and not for diagnosis.

The A1C test is a valuable tool for diabetes management and early detection of prediabetes and type 2 diabetes. It does not require fasting before the test, and results are usually available quickly. However, it should not be used to diagnose type 1 diabetes, gestational diabetes, or cystic fibrosis-related diabetes, as it may give false results in certain cases.

Urine test

In addition to testing for glucose and ketones, urine tests can also be used to check for protein levels, which can indicate kidney disease, a common complication of diabetes. A test called a microalbuminuria test can detect small amounts of albumin, the main protein in blood, in the urine. This test is recommended for people with type 2 diabetes to monitor their kidney health.

Frequently asked questions