Diabetes Insipidus vs. Diabetes Mellitus

Medically Reviewed by Michael Dansinger, MD on February 13, 2024
4 min read

Diabetes mellitus and diabetes insipidus share the first word of their name and some of the same symptoms. But that’s where the similarities end. These two diseases aren’t related. They cause different problems and have very different treatments.

Diabetes mellitus is more commonly known simply as diabetes. It’s when your pancreas doesn’t produce enough insulin to control the amount of glucose, or sugar, in your blood.

Diabetes insipidus is a rare condition that has nothing to do with the pancreas or blood sugar. Instead, it happens when your kidneys produce a lot of extra pee. Normally, they filter your bloodstream to make about a quart or 2 each day. When you have diabetes insipidus, it’s more like 3 to 20 quarts, and it’s mostly water. This dramatic loss of fluid makes you really thirsty.

Though diabetes mellitus and diabetes insipidus have similar symptoms, these symptoms have different causes.

Exhaustion: With diabetes insipidus, you may feel extremely tired due to dehydration. It also may be because you’re low on electrolytes, such as sodium, potassium, or calcium, which get flushed out with all the pee.

If you have diabetes mellitus, you may feel really tired when your blood sugar levels are either too low or too high.

Thirst: Diabetes insipidus makes you feel very thirsty because so many fluids are leaving your body. With diabetes mellitus, you feel thirsty because of too much glucose in your blood. Your body wants you to drink more water to flush out the sugar.

Blurred vision: Long periods of dehydration can lead to blurry vision if you have diabetes insipidus. With diabetes mellitus, it’s because you have too much glucose in your blood.

There are a few blood tests to diagnose diabetes mellitus. One is the fasting glucose test. This is when a doctor draws blood after you haven’t eaten for at least 8 hours. The other test is the A1c, or glycated hemoglobin test. You don’t have to fast for this one. Your scores will determine if your doctor may diagnose you with either prediabetes or diabetes.

Doctors also diagnose diabetes insipidus in several ways:

Blood test: Instead of glucose, this blood test measures your sodium levels.

Urinalysis: This test shows how concentrated or dilute (watery) your pee is. Your doctor might even ask you to collect it for 24 hours to see how much you make in that time.

Fluid deprivation test: There are two types: a short form of the test you can do at home and a longer one you do in the hospital. For the short test, your doctor will tell you to stop drinking fluids at a certain time, often dinnertime. The next morning, you’ll collect a urine sample and take it to your doctor.

For the longer fluid restriction test, you’ll be in the hospital. A doctor will weigh you and take a urine sample. They’ll repeat those steps every 1-2 hours while you don’t drink fluids. They’ll also take your blood pressure. They’re looking for one of three things to happen:

  • Your blood pressure drops, and your heartbeat speeds up when you stand up.
  • You lose 5% or more of your body weight.
  • Your urine is still not concentrated after 3 straight tests.

Magnetic resonance imaging (MRI): An MRI can’t diagnose diabetes insipidus. But it can show problems with your hypothalamus or pituitary gland. These issues can cause the disease. They can be because of a gene mutation or damage from a head injury, surgery, infection, or a tumor. The damage upsets the way these parts of your brain make, store, and release vasopressin. This is a hormone that helps your kidneys absorb water and control the flow of urine.

There’s no cure for diabetes mellitus or diabetes insipidus, but you can manage them.

If you have type 1 or type 2 diabetes, you’ll usually manage your blood sugar with insulin shots or other medications. Check it daily to make sure it’s in a safe range. You’ll need to eat a healthy diet and get regular exercise to keep your weight, cholesterol, and blood pressure down. See your doctor for regular checkups.

Treatment for diabetes insipidus depends on which of the four types you have:

  • Central: A synthetic hormone called desmopressin can replace the vasopressin your body doesn’t make to manage your symptoms. It comes as a nasal spray, shot, or pill.
  • Nephrogenic: Diuretics (drugs that help your body get rid of excess sodium and water) and aspirin or ibuprofen can help with symptoms of nephrogenic diabetes insipidus. Your doctor also may check to make sure that the calcium and potassium in your body are in balance. Sometimes this type can go away once you treat it.
  • Dipsogenic: In dipsogenic diabetes insipidus, the problems with your hypothalamus and pituitary gland extend to your thirst mechanism. This means that even though you’re losing a lot of fluid, you’re still not thirsty. Doctors are still at work on a treatment, but for now, they suggest that you suck on ice chips or hard, sour candy to trigger your urge to drink.
  • Gestational: This type of diabetes insipidus can happen when you’re pregnant. Doctors often treat this with desmopressin. Most women don’t continue to need treatment after they give birth.