Diagnosis & Testing

Type 2 Diagnosis and Testing: an introduction

Type 2 diabetes is a significant public health problem worldwide. In the US alone, the Centers for Disease Control and Prevention (CDC) estimated that in 2010 diabetes affected 25.8 million people (that’s 8.3% of the population) and most of these had type 2 diabetes. Among these, 18.8 million were diagnosed and 7 million were undiagnosed. Type 2 diabetes was most common in people 65 years of age or older, occurring in approximately 27% of this age group.1

The statistics are even more sobering if you consider the percentages of adults in the US with prediabetes. Based on statistics from 2005 to 2008, the CDC found that 35% of US adults (age 20 years and older) had prediabetes, with the highest rate among adults 65 years of age and older. Prediabetes affects 1 in 2 adults (50%) in this age range. When these percentages are applied to the entire population of the US (2010 census data), this translates to 79 million adults 20 years of age or older with prediabetes. 1

What makes diabetes such a dangerous public health problem is that if it remains untreated (or undiagnosed) over time it can lead to major health complications, including heart disease, stroke, kidney disease, and other problems. So, early detection and diagnosis of type 2 diabetes (preferably in the prediabetes stage before it becomes type 2 diabetes), followed by effective treatment, is very important.2

A story of hormonal imbalance affecting multiple organs

What happens in type 2 diabetes is that the body loses the ability to use insulin effectively (this is called “insulin resistance”). Insulin is a hormone produced in the beta cells of the pancreas (an organ located behind the stomach) and serves as sort of a “gate keeper,” allowing glucose to enter cells where it can be transformed into energy and used to support vital cell functions. In addition to insulin, the other hormones involved in glucose control include amylin, a group of hormones called incretins, which are produced in the intestine, and glucagon, which is produced in the pancreas. Type 2 diabetes appears to involve abnormalities in all of these hormones. In type 2 diabetes, being overweight starts the process of events inside the body that leads to the development of insulin resistance and hormonal imbalance.3,4

In addition to insulin resistance, loss of the ability to produce insulin also plays a role in elevated blood glucose. In fact, by the time that most people are diagnosed with type 2 diabetes, they have already lost over 50% of their ability to make the insulin they need. The process that leads to the development of type 2 diabetes, involving insulin resistance and loss of the ability to produce insulin, can begin well before a person is diagnosed with type 2 diabetes. In many people, insulin resistance and decreased insulin production develops over a period of 5 to 10 years before high blood sugar is detected.5

Just as there are multiple hormones in the body that are involved in the disease process of type 2 diabetes, the latest research also shows that high blood glucose in type 2 diabetes is driven not by a single organ, such as the pancreas, but by multiple organs and tissues. In fact, nowadays when researchers consider type 2 diabetes, they think of the “ominous octet” or organs and tissues that work together to contribute to elevated blood glucose. This octet includes6

  • Muscle
  • Fat cells
  • Liver
  • Beta cells in the pancreas
  • Alpha cells in the pancreas
  • Intestine
  • Kidney
  • Brain

How is diabetes diagnosed?

Most people who develop type 2 diabetes will not experience the classic symptoms of high blood sugar, which include frequent urination, excessive thirst, urination at night, blurred vision and, in some cases, weight loss. Therefore, measuring excess blood sugar or blood glucose levels is the main way to diagnose diabetes. In most cases, diabetes will be detected during routine laboratory testing as part of a check-up.

Diagnosing diabetes: blood sugar testing


Test results

Random blood sugar 200 mg/dL or higher+ classic symptoms of high blood sugar
Fasting blood glucose* 126 mg/dL or higher**
Oral glucose tolerance† 200 mg/dL or higher**
Hemoglobin A1C 6.5% or higher**

*Fasting defined as not eating or drinking for 8 to 12 hours (typically over night, with blood drawn in morning).

**Diagnosis requires confirmation by repeat testing.

†Result 2 hours after oral glucose test.

Four different tests are used to measure blood glucose and can be used to diagnose diabetes. These include7,8:

  • Random blood sugar test: blood test taken at any time during the day, regardless of when you last ate
  • Fasting blood sugar test: blood test taken after fasting (not eating or drinking) for 8 to 12 hours (typically you fast overnight and have blood drawn in the morning)
  • Oral glucose tolerance test: blood test taken before and 2 hours after drinking a special glucose solution
  • Hemoglobin A1C test (known as “A1C”): blood test taken at any time of day (before or after a meal) that measures average blood sugar level over a 2 to 3 month period.

According to the American Diabetes Association (ADA) diagnostic criteria, diabetes can be diagnosed using a random blood sugar test of 200 mg/dLor higher with symptoms associated with high blood sugar, or on the basis of repeated abnormal readings on either fasting blood glucose, oral glucose tolerance, or hemoglobin A1C tests.8

Written by: Jonathan Simmons | Last reviewed: May 2014.
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