Diagnosis of Diabetes


What is diabetes?

Diabetes is a disease in which levels of blood glucose, also called blood sugar, are above normal. People with diabetes have problems converting food to energy. Normally, after a meal, the body breaks food down into glucose, which the blood carries to cells throughout the body. Cells use insulin, a hormone made in the pancreas, to help them convert blood glucose into energy.

People develop diabetes because the pancreas does not make enough insulin or because the cells in the muscles, liver, and fat do not use insulin properly, or both. As a result, the amount of glucose in the blood increases while the cells are starved of energy. Over the years, high blood glucose, also called hyperglycemia, damages nerves and blood vessels, which can lead to complications such as heart disease, stroke, kidney disease, blindness, nerve problems, gum infections, and amputation.

Main Types of Diabetes

The two main types of diabetes are called type 1 and type 2. A third form of diabetes is called gestational diabetes.

  • Type 1 diabetes, formerly called juvenile diabetes, is usually first diagnosed in children, teenagers, and young adults. In this form of diabetes, the pancreas no longer makes insulin because the body’s immune system has attacked and destroyed the pancreatic cells specialized to make insulin. These insulin-producing cells are called beta cells.
  • Type 2 diabetes, formerly called adult-onset diabetes, is the most common form. People can develop type 2 diabetes at any age, even during childhood. This form of diabetes usually begins with insulin resistance, a condition in which muscle, liver, and fat cells do not use insulin properly. As a result, the body needs more insulin to help glucose enter cells to be used for energy. At first, the pancreas keeps up with the added demand by producing more insulin. In time, however, the pancreas loses its ability to secrete enough insulin in response to meals.
  • Gestational diabetes is diabetes that first occurs during pregnancy. When women are pregnant, their need for insulin appears to increase, and many can develop gestational diabetes during the late stages of pregnancy. Although this form of diabetes usually goes away after the baby is born, a woman who has had it is more likely to develop type 2 diabetes later in life.

Other Types of Diabetes

A number of other types of diabetes exist. A person may exhibit characteristics of more than one type. For example, in latent autoimmune diabetes in adults (LADA), also called type 1.5 diabetes or double diabetes, people show signs of both type 1 and type 2 diabetes. Diagnosis usually occurs after age 30.

Most people with LADA still produce their own insulin when first diagnosed, like those with type 2 diabetes, but within a few years, they must take insulin to control blood glucose levels. In LADA, as in type 1 diabetes, the beta cells of the pancreas stop making insulin because the body’s immune system attacks and destroys them. Some experts believe that LADA is a slowly developing kind of type 1 diabetes.

Other types of diabetes include those caused by

  • genetic defects of the beta cell, such as maturity-onset diabetes of the young (MODY) and neonatal diabetes mellitus
  • genetic defects in insulin action, resulting in the body’s inability to control blood glucose levels, as seen in leprechaunism and the Rabson-Mendenhall syndrome
  • diseases of the pancreas or conditions that damage the pancreas, such as pancreatitis and cystic fibrosis
  • excess amounts of certain hormones resulting from some medical conditions—such as cortisol in Cushing’s syndrome—that work against the action of insulin
  • medications that reduce insulin action, such as glucocorticoids, or chemicals that destroy beta cells
  • infections, such as congenital rubella and cytomegalovirus
  • rare autoimmune disorders, such as stiff-man syndrome, an autoimmune disease of the central nervous system
  • genetic syndromes associated with diabetes, such as Down syndrome and Prader-Willi syndrome

More information about MODY and neonatal diabetes mellitus is in the National Diabetes Information Clearinghouse’s fact sheet Monogenic Forms of Diabetes: Neonatal Diabetes Mellitus and Maturity-onset Diabetes of the Young. The fact sheet is available at diabetes.niddk.nih.gov/dm/pubs/mody/index.htm or by calling 1–800–860–8747.

Type 1 and type 2

diabetesIn 1997, to move away from naming the two main types of diabetes based on treatment or the age at onset, an American Diabetes Association expert committee recommended universal adoption of simplified terminology. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) agrees.

What is pre-diabetes?

In pre-diabetes, blood glucose levels are higher than normal but not high enough for a diagnosis of diabetes. However, many people with pre-diabetes develop type 2 diabetes within 10 years. Experts disagree about the specific blood glucose level they should use to diagnose diabetes, and through the years, that number has changed. Individuals with pre-diabetes have an increased risk of heart disease and stroke. With modest weight loss and moderate physical activity, people with pre-diabetes can delay or prevent type 2 diabetes.

[Top]

Former Name Preferred Names
Type I

juvenile diabetes

insulin-dependent
diabetes mellitus

IDDM

type 1 diabetes
Type II

adult-onset diabetes

noninsulin-dependent
diabetes mellitus

NIDDM

type 2 diabetes

How are diabetes and pre-diabetes diagnosed?

The following tests are used for diagnosis:

  • A fasting plasma glucose (FPG) test measures blood glucose in a person who has not eaten anything for at least 8 hours. This test is used to detect diabetes and pre-diabetes.
  • An oral glucose tolerance test (OGTT) measures blood glucose after a person fasts at least 8 hours and 2 hours after the person drinks a glucose-containing beverage. This test can be used to diagnose diabetes and pre-diabetes.
  • A random plasma glucose test, also called a casual plasma glucose test, measures blood glucose without regard to when the person being tested last ate. This test, along with an assessment of symptoms, is used to diagnose diabetes but not pre-diabetes.

Test results indicating that a person has diabetes should be confirmed with a second test on a different day.

FPG Test

The FPG test is the preferred test for diagnosing diabetes because of its convenience and low cost. However, it will miss some diabetes or pre-diabetes that can be found with the OGTT. The FPG test is most reliable when done in the morning. Results and their meaning are shown in Table 1. People with a fasting glucose level of 100 to 125 milligrams per deciliter (mg/dL) have a form of pre-diabetes called impaired fasting glucose (IFG). Having IFG means a person has an increased risk of developing type 2 diabetes but does not have it yet. A level of 126 mg/dL or above, confirmed by repeating the test on another day, means a person has diabetes.

Table 1. FPG
test
Plasma Glucose
Result (mg/dL)
Diagnosis
99 or below Normal
100 to 125 Pre-diabetes
(impaired fasting
glucose)
126 or above Diabetes*

*Confirmed by repeating the test on a different day.

OGTT

Research has shown that the OGTT is more sensitive than the FPG test for diagnosing pre-diabetes, but it is less convenient to administer. The OGTT requires fasting for at least 8 hours before the test. The plasma glucose level is measured immediately before and 2 hours after a person drinks a liquid containing 75 grams of glucose dissolved in water. Results and their meaning are shown in Table 2. If the blood glucose level is between 140 and 199 mg/dL 2 hours after drinking the liquid, the person has a form of pre-diabetes called impaired glucose tolerance (IGT). Having IGT, like having IFG, means a person has an increased risk of developing type 2 diabetes but does not have it yet. A 2-hour glucose level of 200 mg/dL or above, confirmed by repeating the test on another day, means a person has diabetes.

Table 2. OGTT
2-Hour Plasma
Glucose Result
(mg/dL)
Diagnosis
139 and below Normal
140 to 199 Pre-diabetes
(impaired glucose
tolerance)
200 and above Diabetes*

*Confirmed by repeating the test on a different day.

Gestational diabetes is also diagnosed based on plasma glucose values measured during the OGTT, preferably by using 100 grams of glucose in liquid for the test. Blood glucose levels are checked four times during the test. If blood glucose levels are above normal at least twice during the test, the woman has gestational diabetes. Table 3 shows the above-normal results for the OGTT for gestational diabetes.
Table 3.
Gestational diabetes:
Above-normal results for
the OGTT*
When Plasma Glucose
Result (mg/dL)
Fasting 95 or higher
At 1 hour 180 or higher
At 2 hours 155 or higher
At 3 hours 140 or higher

Note: Some laboratories use other numbers for this test.
*These numbers are for a test using a drink with 100 grams of glucose.

Additional information about the diagnosis and treatment of gestational diabetes is in the publication What I need to know about Gestational Diabetes. This publication is available at diabetes.niddk.nih.gov/dm/pubs/gestational/index.htm or by calling 1–800–860–8747.

Random Plasma Glucose Test

A random, or casual, blood glucose level of 200 mg/dL or higher, plus the presence of the following symptoms, can mean a person has diabetes:

  • increased urination
  • increased thirst
  • unexplained weight loss

Other symptoms can include fatigue, blurred vision, increased hunger, and sores that do not heal. The doctor will check the person’s blood glucose level on another day using the FPG test or the OGTT to confirm the diagnosis.

[Top]

Who should be tested for diabetes and pre-diabetes?

The American Diabetes Association recommends that testing to detect pre-diabetes and type 2 diabetes be considered in adults without symptoms who are overweight or obese and have one or more additional risk factors for diabetes. In those without these risk factors, testing should begin at age 45. The Body Mass Index Table can be used to find out whether someone is normal weight, overweight, obese, or extremely obese.

People aged 45 or older should consider getting tested for pre-diabetes or diabetes. People younger than 45 should consider testing if they are overweight, obese, or extremely obese and have one or more of the following risk factors:

  • being physically inactive
  • having a parent, brother, or sister with diabetes
  • having a family background that is African American, Alaska Native, American Indian, Asian American, Hispanic/Latino, or Pacific Islander
  • giving birth to a baby weighing more than 9 pounds or being diagnosed with gestational diabetes
  • having high blood pressure—140/90 mmHg or above—or being treated for high blood pressure
  • having an HDL, or “good,” cholesterol level below 35 mg/dL or a triglyceride level above 250 mg/dL
  • having polycystic ovary syndrome, also called PCOS
  • having IFG or IGT on previous testing
  • having a condition called acanthosis nigricans, characterized by a dark, velvety rash around the neck or armpits
  • having a history of cardiovascular disease—disease affecting the heart and blood vessels

If results of testing are normal, testing should be repeated at least every 3 years. Doctors may recommend more frequent testing depending on initial results and risk status. People whose test results indicate they have pre-diabetes should have their blood glucose checked again in 1 to 2 years and take steps to prevent type 2 diabetes.

When a woman is pregnant, the doctor will assess her risk for developing gestational diabetes at her first prenatal visit and order testing as needed during the pregnancy. Women who develop gestational diabetes should also have follow-up testing 6 to 12 weeks after the baby is born.

Type 2 diabetes has become more common in children and teens than in the past, and those at high risk for developing diabetes should be tested every 2 years. Testing should begin at age 10 or at puberty, whichever occurs first. Children and teens who are overweight or obese and have other risk factors, such as a family history of diabetes, are at high risk for developing diabetes.

[Top]

Body Mass Index (BMI)

BMI is a measurement of body weight relative to height. Adults aged 20 or older can use the BMI Table to find out whether they are normal weight, overweight, obese, or extremely obese. To use the table,

  • find the adult’s height in the left-hand column
  • move across the row to the number closest to that person’s weight
  • find the number at the top of that column

The number at the top of the column is the person’s BMI. The words above the BMI number indicate whether the person is normal weight, overweight, obese, or extremely obese. People who are overweight, obese, or extremely obese should consider talking with a doctor about ways to lose weight to reduce the risk of diabetes.

The BMI has certain limitations. It may overestimate body fat in athletes and others who have a muscular build and underestimate body fat in older adults and others who have lost muscle.

BMI for children and teens must be determined based on age, height, weight, and sex. The Centers for Disease Control and Prevention (CDC) has information about BMI in children and teens, including a BMI calculator, at www.cdc.gov/nccdphp/dnpa/bmi. The CDC website also has a BMI calculator for adults.

For a printer-friendly version of this table, use the pdf. (PDF, 34 KB) *

Table 4. Body Mass Index
Normal Overweight Obese
BMI 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
Height
(inches)
Body Weight
(pounds)
58 91 96 100 105 110 115 119 124 129 134 138 143 148 153 158 162 167
59 94 99 104 109 114 119 124 128 133 138 143 148 153 158 163 168 173
60 97 102 107 112 118 123 128 133 138 143 148 153 158 163 168 174 179
61 100 106 111 116 122 127 132 137 143 148 153 158 164 169 174 180 185
62 104 109 115 120 126 131 136 142 147 153 158 164 169 175 180 186 191
63 107 113 118 124 130 135 141 146 152 158 163 169 175 180 186 191 197
64 110 116 122 128 134 140 145 151 157 163 169 174 180 186 192 197 204
65 114 120 126 132 138 144 150 156 162 168 174 180 186 192 198 204 210
66 118 124 130 136 142 148 155 161 167 173 179 186 192 198 204 210 216
67 121 127 134 140 146 153 159 166 172 178 185 191 198 204 211 217 223
68 125 131 138 144 151 158 164 171 177 184 190 197 203 210 216 223 230
69 128 135 142 149 155 162 169 176 182 189 196 203 209 216 223 230 236
70 132 139 146 153 160 167 174 181 188 195 202 209 216 222 229 236 243
71 136 143 150 157 165 172 179 186 193 200 208 215 222 229 236 243 250
72 140 147 154 162 169 177 184 191 199 206 213 221 228 235 242 250 258
73 144 151 159 166 174 182 189 197 204 212 219 227 235 242 250 257 265
74 148 155 163 171 179 186 194 202 210 218 225 233 241 249 256 264 272
75 152 160 168 176 184 192 200 208 216 224 232 240 248 256 264 272 279
76 156 164 172 180 189 197 205 213 221 230 238 246 254 263 271 279 287
Body Mass Index Table 2
of 2
Obese Extreme Obesity
BMI 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
Height
(inches)
Body Weight
(pounds)
58 172 177 181 186 191 196 201 205 210 215 220 224 229 234 239 244 248 253 258
59 178 183 188 193 198 203 208 212 217 222 227 232 237 242 247 252 257 262 267
60 184 189 194 199 204 209 215 220 225 230 235 240 245 250 255 261 266 271 276
61 190 195 201 206 211 217 222 227 232 238 243 248 254 259 264 269 275 280 285
62 196 202 207 213 218 224 229 235 240 246 251 256 262 267 273 278 284 289 295
63 203 208 214 220 225 231 237 242 248 254 259 265 270 278 282 287 293 299 304
64 209 215 221 227 232 238 244 250 256 262 267 273 279 285 291 296 302 308 314
65 216 222 228 234 240 246 252 258 264 270 276 282 288 294 300 306 312 318 324
66 223 229 235 241 247 253 260 266 272 278 284 291 297 303 309 315 322 328 334
67 230 236 242 249 255 261 268 274 280 287 293 299 306 312 319 325 331 338 344
68 236 243 249 256 262 269 276 282 289 295 302 308 315 322 328 335 341 348 354
69 243 250 257 263 270 277 284 291 297 304 311 318 324 331 338 345 351 358 365
70 250 257 264 271 278 285 292 299 306 313 320 327 334 341 348 355 362 369 376
71 257 265 272 279 286 293 301 308 315 322 329 338 343 351 358 365 372 379 386
72 265 272 279 287 294 302 309 316 324 331 338 346 353 361 368 375 383 390 397
73 272 280 288 295 302 310 318 325 333 340 348 355 363 371 378 386 393 401 408
74 280 287 295 303 311 319 326 334 342 350 358 365 373 381 389 396 404 412 420
75 287 295 303 311 319 327 335 343 351 359 367 375 383 391 399 407 415 423 431
76 295 304 312 320 328 336 344 353 361 369 377 385 394 402 410 418 426 435 443

In addition to weight, the location of excess fat on the body can be important. A waist measurement of 40 inches or more for men or 35 inches or more for women is linked to insulin resistance and increases a person’s risk for type 2 diabetes.

[Top]

What steps can delay or prevent type 2 diabetes?

A major research study, the Diabetes Prevention Program (DPP), confirmed that people with IGT—pre-diabetes—were able to sharply reduce their risk of developing diabetes during the study by losing 5 to 7 percent of their body weight through dietary changes and increased physical activity. Study participants followed a low-fat, low-calorie diet and engaged in regular physical activity, such as walking briskly for 30 minutes, five times a week. These strategies worked well for both men and women and were especially effective for participants aged 60 and older.

More information about insulin resistance, the DPP, or how to lower risk for type 2 diabetes is available in the following publications:

These publications are available at www.diabetes.niddk.nih.gov or by calling 1–800–860–8747.

The National Diabetes Education Program (NDEP) offers several booklets as part of its Small Steps, Big Rewards campaign on preventing type 2 diabetes, including information about setting goals, tracking progress, implementing a walking program, and finding additional resources. These materials are available at www.ndep.nih.gov or by calling the NDEP at 1–888–693–NDEP (6337).

[Top]

How is diabetes managed?

People with diabetes can manage it with meal planning, physical activity, and, if needed, medications. Additional information about taking care of type 1 or type 2 diabetes is available in the publication Your Guide to Diabetes: Type 1 and Type 2. This publication is available at diabetes.niddk.nih.gov/dm/pubs/type1and2/index.htm or by calling 1–800–860–8747.

[Top]

Points to Remember

  • Diabetes, pre-diabetes, and gestational diabetes are diagnosed by checking blood glucose levels.
  • Tests used for diagnosing diabetes and pre-diabetes include the fasting plasma glucose (FPG) test and the oral glucose tolerance test (OGTT).
  • People aged 45 or older should consider getting tested for pre-diabetes or diabetes. People younger than 45 who are overweight, obese, or extremely obese and have one or more additional risk factors for diabetes should consider testing.
  • Many people with pre-diabetes develop type 2 diabetes within 10 years.
  • People with pre-diabetes can delay or prevent type 2 diabetes by losing a modest amount of weight through regular physical activity and a diet low in fat and calories.

[Top]

Hope through Research

The NIDDK conducts and supports research related to the causes, treatment, and prevention of diabetes.

Participants in clinical trials can play a more active role in their own health care, gain access to new research treatments before they are widely available, and help others by contributing to medical research. For information about current studies, visit www.ClinicalTrials.gov.

[Top]