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Diagnosis of Diabetes

Last Update: November 3, 2008

What is diabetes?

Diabetes is a disease in which blood glucose levels are above normal. People with diabetes have problems converting food to energy. After a meal, food is broken down into a sugar called glucose, which is carried by the blood 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 and stroke, kidney disease, blindness, nerve problems, gum infections, and amputation.

Types of Diabetes

The three main types of diabetes are type 1, type 2, and gestational diabetes.

  • Type 1 diabetes, formerly called juvenile diabetes, is usually first diagnosed in children, teenagers, or young adults. In this form of diabetes, the beta cells of the pancreas no longer make insulin because the body's immune system has attacked and destroyed them.

  • Type 2 diabetes, formerly called adult-onset diabetes, is the most common form. People can develop it 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. At first, the pancreas keeps up with the added demand by producing more insulin. In time, however, it loses the ability to secrete enough insulin in response to meals.

  • Gestational diabetes develops in some women 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. Gestational diabetes is caused by the hormones of pregnancy or by a shortage of insulin.

Type 1 Diabetes and Type 2 Diabetes

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

Former Names 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

What is pre-diabetes?

In pre-diabetes, blood glucose levels are higher than normal but not high enough to be characterized as diabetes. However, many people with pre-diabetes develop type 2 diabetes within 10 years. Pre-diabetes also increases the 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.

How are diabetes and pre-diabetes diagnosed?

The following tests are used for diagnosis:

  • A fasting plasma glucose test measures your blood glucose after you have gone at least 8 hours without eating. This test is used to detect diabetes or pre-diabetes.

  • An oral glucose tolerance test measures your blood glucose after you have gone at least 8 hours without eating and 2 hours after you drink a glucose-containing beverage. This test can be used to diagnose diabetes or pre-diabetes.

  • In a random plasma glucose test, your doctor checks your blood glucose without regard to when you ate your last meal. This test, along with an assessment of symptoms, is used to diagnose diabetes but not pre-diabetes.

Positive test results should be confirmed by repeating the fasting plasma glucose test or the oral glucose tolerance test on a different day.

Fasting Plasma Glucose (FPG) Test

The FPG is the preferred test for diagnosing diabetes due to convenience and is most reliable when done in the morning. Results and their meaning are shown in table 1. If your fasting glucose level is 100 to 125 mg/dL, you have a form of pre-diabetes called impaired fasting glucose (IFG), meaning that you are more likely to develop type 2 diabetes but do not have it yet. A level of 126 mg/dL or above, confirmed by repeating the test on another day, means that you have diabetes.

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

*Confirmed by repeating the test on a different day.

Oral Glucose Tolerance Test (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 you to fast for at least 8 hours before the test. Your plasma glucose is measured immediately before and 2 hours after you drink a liquid containing 75 grams of glucose dissolved in water. If your blood glucose level is between 140 and 199 mg/dL 2 hours after drinking the liquid, you have a form of pre-diabetes called impaired glucose tolerance or IGT, meaning that you are more likely to develop type 2 diabetes but do not have it yet. A 2-hour glucose level of 200 mg/dL or above, confirmed by repeating the test on another day, means that you have diabetes.

Table 2. Oral Glucose Tolerance Test
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. Blood glucose levels are checked four times during the test. If your blood glucose levels are above normal at least twice during the test, you have gestational diabetes. Table 3 shows the above-normal results for the OGTT for gestational diabetes.

Table 3. Gestational Diabetes: Above-Normal
Results for the Oral Glucose Tolerance Test

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.

Random Plasma Glucose Test

A random blood glucose level of 200 mg/dL or more, plus presence of the following symptoms, can mean that you have diabetes:

  • increased urination
  • increased thirst
  • unexplained weight loss

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

What factors increase my risk for type 2 diabetes?

To find out your risk, check each item that applies to you.

  • I am 45 or older.

  • I am overweight or obese (see the body mass index [BMI] in table 4).

  • I have a parent, brother, or sister with diabetes.

  • My family background is African American, American Indian, Asian American, Pacific Islander, or Hispanic American/Latino.

  • I have had gestational diabetes, or I gave birth to at least one baby weighing more than 9 pounds.

  • My blood pressure is 140/90 or higher, or I have been told that I have high blood pressure.

  • My cholesterol levels are not normal. My HDL cholesterol ("good" cholesterol) is 35 or lower, or my triglyceride level is 250 or higher.

  • I am fairly inactive. I exercise fewer than three times a week.

Checking My Weight

BMI is a measure used to evaluate body weight relative to height. You can use BMI to find out whether you are underweight, normal weight, overweight, or obese. Use table 4 to find your BMI.

  • Find your height in the left-hand column.
  • Move across in the same row to the number closest to your weight.

The number at the top of that column is your BMI. Check the word above your BMI to see whether you are normal weight, overweight, or obese. If you are overweight or obese, talk with your doctor about ways to lose weight to reduce your risk of diabetes or pre-diabetes.

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

When should I be tested for diabetes?

Anyone 45 years old or older should consider getting tested for diabetes. If you are 45 or older and your BMI indicates that you are overweight, it is strongly recommended that you get tested. If you are younger than 45, are overweight, and have one or more of the risk factors, you should consider testing. Ask your doctor for a FPG or an OGTT. Your doctor will tell you if you have normal blood glucose, pre-diabetes, or diabetes. If your blood glucose is higher than normal but lower than the diabetes range (called pre-diabetes), have your blood glucose checked in 1 to 2 years.

What steps can delay or prevent type 2 diabetes?

A major research study, the Diabetes Prevention Program, confirmed that people who followed a low-fat, low-calorie diet, lost a modest amount of weight, and engaged in regular physical activity (walking briskly for 30 minutes, five times a week, for example) sharply reduced their chances of developing diabetes. These strategies worked well for both men and women and were especially effective for participants aged 60 and older.

How is diabetes managed?

If you are diagnosed with diabetes, you can manage it with meal planning, physical activity, and, if needed, medications.

Points to Remember

  • Diabetes and pre-diabetes are diagnosed by checking blood glucose levels.

  • Many people with pre-diabetes develop type 2 diabetes within 10 years.

  • If you have pre-diabetes, you can delay or prevent type 2 diabetes with a low-fat, low-calorie diet, modest weight loss, and regular physical activity.

  • If you are 45 or older, you should consider getting tested for diabetes. If you are 45 or older and overweight, it is strongly recommended that you get tested.

  • If you are younger than 45, are overweight, and have one or more of the risk factors, you should consider testing.
This article originally appeared at http://diabetes.niddk.nih.gov/dm/pubs/diagnosis/index.htm


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